Astronomy Archives

April 16, 2015December 23, 2015 by Joshua Carroll

Stars: A Day in the Life

There is something about them that intrigues us all. These massive spheres of gas burning intensely from the energy of fusion buried many thousands of kilometers deep within their cores. The stars have been the object of humanity’s wonderment for as far back as we have records. Many of humanity’s religions can be tied to worshiping these celestial candles. For the Egyptians, the sun was representative of the God Ra, who each day vanquished the night and brought light and warmth to the lands. For the Greeks, it was Apollo who drove his flaming chariot across the sky, illuminating the world. Even in Christianity, Jesus can be said to be representative of the sun given the striking characteristics his story holds with ancient astrological beliefs and figures. In fact, many of the ancient beliefs follow a similar path, all of which tie their origins to that of the worship of the sun and stars.

Humanity thrived off of the stars in the night sky because they recognized a correlation in the pattern in which certain star formations (known as constellations) represented specific times in the yearly cycle. One of which meant that it was to become warmer soon, which led to planting food. The other constellations foretold the coming of a

The familiar constellation of Orion. Orion's Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner) Credit: NASA Astronomy Picture of the Day Collection NASA — The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner)
Credit: NASA Astronomy Picture of the Day Collection
NASA

colder period, so you were able to begin storing food and gathering firewood. Moving forward in humanity’s journey, the stars then became a way to navigate. Sailing by the stars was the way to get around, and we owe our early exploration to our understandings of the constellations. For many of the tens of thousands of years that human eyes have gazed upwards toward the heavens, it wasn’t until relatively recently that we fully began to understand what stars actually were, where they came from, and how they lived and died. This is what we shall discuss in this article. Come with me as we venture deep into the cosmos and witness physics writ large, as I cover how a star is born, lives, and eventually dies.

We begin our journey by traveling out into the universe in search of something special. We are looking for a unique structure where both the right circumstances and ingredients are present. We are looking for what astronomer’s call a Dark Nebula. I’m sure you’ve heard of nebulae before, and have no doubt seen them. Many of the amazing images that the Hubble Space Telescope has obtained are of beautiful gas clouds, glowing amidst the backdrop of billions of stars. Their colors range from deep reds, to vibrant blues, and even some eerie greens. This is not the type of nebula we are in search of though. The nebula we need is dark, opaque, and very, very cold.

You may by wondering to yourself, “Why are we looking for something dark and cold when stars are bright and hot?”

http://www.eso.org/public/images/eso1501a/ — Image of a Dark Nebula Credit: ESO http://www.eso.org/public/images/eso1501a

Indeed, this is something that would appear puzzling at first. Why does something need to be cold first before it can become extremely hot? First, we must cover something elementary about what we call the Interstellar Medium (ISM), or the space between the stars. Space is not empty as its name would imply. Space contains both gas and dust. The gas we are mainly referring to is Hydrogen, the most abundant element in the universe. Since the universe is not uniform (the same density of gas and dust over every cubic meter), there are pockets of space that contain more gas and dust than others. This causes gravity to manipulate these pockets to come together and form what we see as nebulae. Many things go into the making of these different nebulae, but the one that we are looking for, a Dark Nebula, possesses very special properties. Now, let us dive into one of these Dark Nebulae and see what is going on.

As we descend through the outer layers of this nebula, we notice that the temperature of the gas and dust is very low. In some nebulae, the temperatures are very hot. The more particles bump into each other, excited by the absorption and emission of exterior and interior radiation, means higher temperatures. But in this Dark Nebula, the opposite is happening. The temperatures are decreasing the further into the cloud we get. The reason these Dark Nebulae have specific properties that work to create a great stellar nursery has to deal with the basic properties of the nebula and the region type that the cloud exists in, which has some difficult concepts associated with it that I will not fully illustrate here. They include the region where the molecular clouds form which are called Neutral Hydrogen Regions, and the properties of these regions have to deal with electron spin values, along with magnetic field interactions that effect said electrons. The traits that I will cover are what allows for this particular nebula to be ripe for star formation.

Excluding the complex science behind what helps form these nebulae, we can begin to address the first question of why must we get colder to get hotter. The answer comes down to gravity. When particles are heated, or excited, they move faster. A cloud with sufficient energy will contain far too much momentum among each of the dust and gas particles for any type of formations to occur. As in, if dust grains and gas atoms are moving too quickly, they will simply bounce off of one another or just shoot past each other, never achieving any type of bond. Without this interaction, you can never have a star. However, if the temperatures are cold enough, the particles of gas and dust are moving so slow that their mutual gravity will allow for them to start to “stick” together. It is this process that allows for a protostar to begin to form.

Generally what supplies energy to allow for the faster motion of the particles in these molecular clouds is radiation. Of course, there is radiation coming in from all directions at all times in the universe. As we see with other nebulae, they are glowing with energy and stars aren’t being born amid these hot gas clouds. They are being heated by external radiation from other stars and from its own internal heat. How does this Dark Nebula prevent external radiation from heating up the gas in the cloud and causing it to move too fast for gravity to take hold? This is where

http://www.eso.org/public/images/eso0102a/ — Barnard 68 is a large molecular cloud that is so thick, it blocks out the light from stars that we normally would be able to see. Credit: ESO http://www.eso.org/public/images/eso0102a

the opaque nature of these Dark Nebulae comes into play. Opacity is the measure of how much light is able to move through an object. The more material in the object or the thicker the object is, the less light is able to penetrate it. The higher frequency light (Gamma Rays, X-Rays, and UV) and even the visible frequencies are affected more by thick pockets of gas and dust. Only the lower frequency types of light, including Infrared, Microwaves, and Radio Waves, has any success of penetrating gas clouds such as these, and even it is somewhat scattered so that generally they do not contain nearly enough energy to begin to disrupt this precarious process of star formation. Thus, the inner portions of the dark gas clouds are effectively “shielded” from the outside radiation that disrupts other, less opaque nebulae. The less radiation that makes it into the cloud, the lower the temperatures of the gas and dust within it. The colder temperatures means less particle motion within the cloud, which is key for what we will discuss next.

Indeed, as we descend towards the core of this dark molecular cloud, we notice that less and less visible light makes it to our eyes, and with special filters, we can see that this is true of other frequencies of light. As a result, the cloud’s temperature is very low. It is worth noting that the process of star formation takes a very long time, and in the interest of not keeping you reading for hundreds of thousands of years, we shall now fast forward time. In a few thousand years, gravity has pulled in a fair amount of gas and dust from the surrounding molecular cloud, causing it to clump together. Dust and gas particles, still shielded from outside radiation, are free to naturally come together and “stick” at these low temperatures. Eventually, something interesting begins to happen. The mutual gravity of this ever growing ball of gas and dust begins a snowball (or star-ball) effect. The more layers of gas and dust that are coagulated together, the denser the interior of this protostar becomes. This density increases the gravitational force near the protostar, thus pulling more material into it. With every dust grain and hydrogen atom that it accumulates, the pressure in the interior of this ball of gas increases.

If you remember anything from any chemistry class you’ve ever taken, you may recall a very special relationship between pressure and temperature when dealing with a gas. PV=nRT, the Ideal Gas Law, comes to mind. Excluding the constant scalar value ‘n’ and the gas constant R ({8.314 J/mol x K}), and solving for Temperature (T), we get T=PV, which means that the temperature of a gas cloud is directly proportional to pressure. If you increase the pressure, you increase the temperature. The core of this soon-to-be star residing in this Dark Nebula is becoming very dense, and the pressure is skyrocketing. According to what we just calculated, that means that the temperature is also increasing.

Artistic rendition of a star forming within a dark nebula. Credit: NASA/JPL-Caltech/R. Hurt (SSC)

We yet again consider this nebula for the next step. This nebula has a large amount of dust and gas (hence it being opaque), which means it has a lot of material to feed our protostar. It continues to pull in the gas and dust from its surrounding environment and begins heating up. The hydrogen particles in the core of this object are bouncing around so quick that they are releasing energy into the star. The protostar begins to get very hot and is now glowing with radiation (generally Infrared). At this point, gravity is still pulling in more gas and dust which is adding to the pressures exerted deep within the core of this protostar. The gas of the Dark Nebula will continue to collapse in on itself until something important happens. When there is little to nothing left near the star to fall onto its surface, it begins to lose energy (due to it radiating away as light). When this happens, that outward force lessens and gravity starts to contract the star faster. This greatly increases the pressure in the core of this protostar. As the pressure grows, the temperature in the core reaches a value that is crucial for the process that we are witnessing. The protostar’s core has become so dense and hot, that it reaches roughly 10 million Kelvin. To put that into perspective, this temperature is roughly 1700x hotter than the surface of our sun (at around 5800K). Why is 10 million Kelvin so important? Because at that temperature, the thermonuclear fusion of Hydrogen can occur, and once fusion starts, this newborn star “turns on” and bursts to life, sending out vast amounts of energy in all directions.

In the core, it is so hot that the electrons that zip around the hydrogen’s proton nuclei are stripped off (ionized), and all you have are free moving protons. If the temperature isn’t hot enough, these free flying protons (which have positive charges), will simply glance off one another. However, at 10 Million Kelvin, the protons are moving so fast that they can get close enough to allow for the Strong Nuclear Force to take over, and when it does the Hydrogen protons begin slamming into each other with enough force to fuse together, creating Helium atoms and releasing lots of energy in the form of radiation. It’s a chain reaction that can be summed up as 4 Protons yield 1 Helium atom + energy. This fusion is what ignites the star and causes it to “burn”. The energy liberated by this reaction goes into helping other Hydrogen protons fuse and also supplies the energy to keep the star from collapsing in on itself. The energy that is pumping out of this star in all directions all comes from the core, and the subsequent layers of this young star all transmit that heat in their own way (using radiation and convection methods depending upon what type of star has been born).

Newborn stars glow through their parent molecular cloud Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt — Newborn stars glow through their parent molecular cloud
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

What we have witnessed now, from the start of our journey when we dove down into that cold Dark Nebula, is the birth of a young, hot star. The nebula protected this star from errant radiation that would have disrupted this process, as well as providing the frigid environment that was needed for gravity to take hold and work its magic. As we witnessed the protostar form, we may also have seen something incredible. If the contents of this nebula are right, such as having a high amount of heavy metals and silicates (left over from the supernovae of previous, more massive stars) what we could begin to see would be planetary formation taking place in the accretion disk of material around the protostar.

Remaining gas and dust in the vicinity of our new star would begin to form dense pockets by the same mechanism of

Artistic rendition of a protoplanet forming within the accretion disk of a protostar Credit: ESO/L. Calçada http://www.eso.org/public/images/eso1310a/ — Artistic rendition of a protoplanet forming within the accretion disk of a protostar
Credit: ESO/L. Calçada
http://www.eso.org/public/images/eso1310a/

gravity, eventually being able to accrete into protoplanets that will be made up of gas or silicates and metal (or a combination of the two). That being said, planetary formation is still somewhat a mystery to us, as there seems to be things that we cannot explain yet at work. But this model of star system formation seems to work well.

The life of the star isn’t nearly as exciting as its birth or death. We will continue to fast forward the clock and watch this star system evolve. Over a few billion years, the remnants of the Dark Nebula have been blown apart and have also formed other stars like the one we witnessed, and it no longer exists. The planets we saw being formed as the protostar grew begin their billion year dance around their parent star. Maybe on one of these worlds, a world that sits at just the right distance away from the star, liquid water exists. Within that water contains the amino acids that are needed for proteins (all composed of the elements that were left over by previous stellar eruptions). These proteins are able to link together to start to form RNA chains, then DNA chains. Maybe at one point a few billion years after the star has been born, we see a space-faring species launch itself into the cosmos, or perhaps they never achieve this for various reasons and remain planet-bound. Of course this is just speculation for our amusement. However, now we come to the end of our journey that began billions of years ago. The star begins to die.

The Hydrogen in its core is being fused into Helium, which depletes the Hydrogen over time; the star is running out of gas. After many years, the hydrogen fusion process begins to stop, and the star puts out less and less energy. This lack of outward pressure from the fusion process upsets what we call the hydrostatic equilibrium, and allows gravity (which is always trying to crush the star) to win. The star begins to shrink rapidly under its own weight. But, just as we discussed earlier, as the pressure increases, so too does the temperature. All of that Helium that was left over

Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium) Credit: NASA — Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium)
Credit: NASA

from the billions of years of hydrogen fusion now begins to heat up in the core. Helium fuses at a much hotter temperature than Hydrogen does, which means that the Helium rich core is able to be pressed inward by gravity without fusing (yet). Since fusion isn’t occurring in the Helium core, there is little to no outward force (given off by fusion) to prevent the core from collapsing. This matter becomes much denser, which we now label as degenerate, and is pushing out massive amounts of heat (gravitational energy becoming thermal energy). This causes the remaining Hydrogen that is in subsequent layers above the Helium core to fuse, which causes the star to expand greatly as this Hydrogen shell burns out of control. This makes the star “rebound” and it expands rapidly; the more energetic fusion from the Hydrogen shells outside of the core expanding the diameter of the star greatly. Our star is now a red giant. Some, if not all of the inner planets that we witnessed form will be incinerated and swallowed up by the star that first gave them life. If there happened to be any life on any of those planets that didn’t manage to leave their home world, they would certainly be erased from the universe, never to be known of.

This process of the star running out of fuel (first Hydrogen, then Helium, etc…) will continue for a while. Eventually, the Helium in the core will reach a certain temperature and begin to fuse into Carbon, which will put off the collapse (and death) of the star. The star we are currently watching live and die is an average-sized Main Sequence Star, so its life ends once it is finished fusing Helium into

Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die Credit: NASA — Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die
Credit: NASA

Carbon. If the star was much larger, this fusion process would proceed until we reached Iron. Iron is the element in which fusion does not take place spontaneously, meaning it requires more energy to fuse it than it gives off after fusion. However, our star will never make it to Iron in its core, and thus it has died after it exhausts its Helium reservoir. When the fusion process finally “turns off” (out of gas), the star slowly begins to cool and the outer layers of the star expand and are ejected into space. Subsequent ejections of stellar material proceed to create what we call a planetary nebula, and all that is left of the once brilliant star we watched spring into existence is now just a ball of dense carbon that will continue to cool for the rest of eternity, possibly crystallizing into diamond.

The death we witnessed just now isn’t the only way a star dies. If a star is sufficiently large enough, its death is much more violent. The star will erupt into the largest explosion in the universe, called a supernova. Depending on many variables, the remnant of the star could end up as a neutron star, or even a black hole. But for most of what we call the average sized Main Sequence Stars, the death that we witnessed will be their fate.

Artistic representation of the material around the supernova 1987A. Credit: ESO/L. Calçada — Artistic representation of the material around the supernova 1987A. Supernovae are among the most violent events in the universe
Credit: ESO/L. Calçada

Our journey ends with us pondering what we have observed. Seeing just what nature can do given the right circumstances, and watching a cloud of very cold gas and dust turn into something that has the potential to breathe life into the cosmos. Our minds wander back to that species that could have evolved on one of those planets. You think about how they may have gone through phases similar to us. Possibly using the stars as supernatural deities that guided their beliefs for thousands of years, substituting answers in for where their ignorance reigned. These beliefs could possibly turn into religions, still grasping that notion of special selection and magnanimous thought. Would the stars fuel their desire to understand the universe as the stars did for us? Your mind then ponders what our fate will be if we do not attempt to take the next step into the universe. Are we to allow our species to be erased from the cosmos as our star expands in its death? This journey you just made into the heart of a Dark Nebula truly exemplifies what the human mind can do, and shows you just how far we have come even though we are still bound to our solar system. The things you have learned were found by others like you simply asking how things occur and then bringing the full weight of our knowledge of physics to bare. Imagine what we can accomplish if we continue this process; being able to fully achieve our place among the stars.

The vastness of space awaits us... Credit: NASA — The vastness of the cosmos awaits us…
Credit: NASA (Hubble Deep Field)

April 14, 2015December 23, 2015 by David Dickinson

Help Researchers Track Comet 67/P Through Perihelion

Calling all light-bucket scope owners: the folks at the European Space Agency want to enlist you in the quest to monitor Comet 67P/Churyumov-Gerasimenko from our Earthbound perspective through perihelion later this summer.

“We are looking to bring an entire community of professional and amateur observers together,” said Rosetta Coordinator of Amateur Observations for Comet 67/P C-G Padma A. Yanamandra-Fisher in a recent press release. “When else can you observe a comet at the same time a spacecraft is viewing it at close proximity and escorting it to perihelion, and be able to correlate both sets of findings?

The Rosetta story thus far has been an amazing tale of discovery. We’ve extensively chronicled the historic approach of the Rosetta spacecraft as the rubber-duck-shaped comet grew in its view here at Universe Today. The world also held its collective breath as the Philae lander, the little washing Euro- washing machine-sized spacecraft that could, descended on to the alien surface. Heck, Philae even knocked a Kardashian out of the top trending spot worldwide, a feat in and of itself.

We also documented the Spinal Tap-esque “None more black” nature of the comet.

Prospects in 2015: As of this writing, Comet 67P/C-G is 1.9 AU from the Sun and closing. The ‘P’ in ‘67/P’ stands for ‘short term (less than 200 years) periodic,’ and the comet orbits the Sun once every 6.44 years. Perihelion for 67/P occurs on August 13^th, 2015 when the comet reaches a distance of 1.24 AU ( 191 million kilometres) from the Sun.

Discovered in 1969 by the Kiev University’s Klim Ivanovych Churyumov while examining a photograph taken by Svetlana Gerasimenko, this is the comet’s seventh apparition. Currently shining at +18th magnitude in the constellation Aquarius, Comet 67P C-G will vault up in the early morning sky for northern hemisphere observers and cross the ecliptic plane in the last week of July, at 43 degrees elongation west of the Sun.

The comet is expected to reach a maximum brightness of +11^th magnitude near perihelion. Historically, 67P – like most comets – tend to under-perform before perihelion, only to have an energetic lingering outburst phase post-perihelion.

“With each apparition we see it (67P) behave differently.” Yanamandra-Fisher said. “These legacy data sets will aid in our knowledge of this comet, especially when used in combination with the data gathered by the Rosetta spacecraft and the new ground observations made this year.”

The path of 67/P through the morning sky as seen from latitude 30 degrees north. Image credit: Starry Night Education software

Time on professional scopes is always chronically in short supply, with more astronomers and targets to observe than there are telescopes available. That’s where amateur observers come in. Many private backyard observatories have instruments that would be the envy of many a major institution. Though the press release suggests that the minimum aperture size needed to observe 67P this summer is 14-inches (35 cm), we urge 10” or 12” inch scope owners – especially those who have the latest generation of Mallincam and faint object CCD imagers – to give it a try. We’ve seen some amazing results with these, even during quick casual observing sessions such as public star parties! The Rosetta team is looking for everything from professional grade images, to sketches and visual observations with magnitude estimations.

Of course, hunting faint comets is a daunting task at best. +10^th magnitude is generally our cut-off for ‘is interesting enough to alert the public’ in terms of novae or comets, though we’ll let 67/P ‘into the club’ due to its celebrity status.

Comet 67/P from June 23rd, 2014. Image credit and copyright: Efrain Morales

To add to the challenge, the comet is only visible against a dark sky during a brief pre-dawn window. You’ll need a planetarium program (we use Starry Night Pro) to generate good finder charts down to 15^th magnitude or so. Keep in mind, comets also typically appear a bit fainter visually than stars of the same magnitude due to the fact that said brightness is spread out over a broad surface area.

ESA also has a great page with an ephemeris generator to help you in your 67/P quest.

“This is truly interactive science that people of all observing levels can participate in- from amateurs to professionals.” Yanamandra-Fischer said in closing.

Other comets to watch for in 2015 include still bright 2014 Q2 Lovejoy, C/2013 US10 Catalina, C/2014 Q1 PanSTARRS, and 19P/Borrelly.

What’ll happen as 67P approaches perihelion? Will those two gigantic lobes crack and separate as Rosetta and the world looks on? Now, I’d pay to see that!

A light bucket scope at the Bruneau Dunes observatory suitable for a faint comet quest. Image credit: David Dickinson

-Register for the Rosetta observation campaign here.

April 13, 2015December 23, 2015 by David Dickinson

Firefly Astronomy

Light makes life, and sometimes, life returns the favor. There’s nothing more magical than watching fireflies flit across a starlit field on a summer’s night. Growing up in Northern Maine, summer was an all-too swiftly passing season, and fireflies had to put on their displays in a brief profusion of frenzied activity around late July and early August before the weather turned once again towards another long harsh winter.

Fireflies remind us of the ephemeral nature of existence, that’s for sure. And they’re much more welcome by summertime campers on vigil for the August Perseids than oh, say the ubiquitous mosquito or vicious black flies…

A recent amazing capture (see the intro image) came to us courtesy of Steed Yu. Shooting from the shores of Lake Natron in Tanzania, he managed to capture an amazing composition of fireflies and those ‘fireflies of the cosmos,’ in the form of a star-dappled southern hemisphere sky.

Taken on February 24^th 2015 just south of the equator, this is simply an amazing image. Don’t forget, though it’s towards the end winter time up here in the northern hemisphere in late February, it’s the tail end of the summer south of the equator.

The photographer had this to say about his ‘Carnival of Fireflies’:

The Night of Lake Natron belongs to the stars. Without any artificial light disturbing the pure sky, one can easily see the Southern Milky Way, as well as sparkling starlights scattered in it, such as the most distinctive constellation Southern Cross and our nearest stellar neighbours Alpha Centauri. The Night of Lake Natron belongs to the firefly too. These glowing elves were flying up and down among the lush grass on both sides of a ravine stream, like a flowing “Firefly Way”, as if to contest with the Milky Way. On the quiet starry night, the fireflies held a grand carnival.

Fireflies shine through a method known as bioluminescence, producing a cold light via a chemical process using the chemical luciferin that causes their abdomen to glow. This aids mating and mate selection, and even firefly larvae have been known to glow. Other deep sea and cave-dwelling species of fish and insects have been known to use a similar signaling method in the absence of ambient light.

You can see the stars of the southern Milky Way and the Southern Cross high above the African night shining in their own particular fashion via nuclear fusion, using the proton-proton chain reaction to shed their ancient photons of light onto the nighttime scene from beyond the cold dust lanes of the Coal Sack.

We’ve managed to observe the sky from the southern hemisphere five times from three different continents over the years, and can attest that all of the ‘good stuff’ is in the southern sky, where the core of our home Milky Way galaxy arcs high overhead.

Such ‘Firefly Time-lapse Astronomy’ is as easy as parking a DSLR with a wide-field of view lens on a tripod and shooting 10-60 second time exposures. Fellow Universe Today writer Bob King wrote a piece last year on his firefly astronomy adventures.

And check out this amazing video sequence by Vincent Brady taken in the summer of 2013 from Lake of the Ozarks, Missouri:

Humans have also mastered the art of creating light and luminescence via technology as well. This has served as a way to ‘push back the night,’ and our 24 hour civilization has come to rely on this mimicry of nature as we demonstrate our prowess at illumination. This often has a cost, however, as we banish the beauty of the night sky to a distant memory. We’ve also had the dubious pleasure of observing and conducting impromptu sidewalk star parties from downtown Tampa and the Las Vegas strip, arguably some of the most light-polluted locales in the world. On such nights, only the Moon, planets and perhaps the odd bright double stars are the only viable targets.

But all is not lost. Perhaps wasteful light pollution is only an adolescent phase that civilizations go through. One SETI search strategy has even suggested that we may be able to detect ET via light pollution from alien cities on the night side of prospective planets … perhaps some race of ‘intelligent fireflies’ straight out of science fiction will use bio-chemical signaling for communication?

All great thoughts to ponder on the star-filled summer nights ahead, as fireflies swarm around us. We move that if we ever become an interstellar species that we bring the noble firefly along for the ride… but please, let’s leave light pollution and mosquitoes behind.

April 9, 2015December 23, 2015 by David Dickinson

Here’s How You Can Watch the SpaceX’s CRS-6 Mission From Your Backyard

Hunting for satellites from your backyard can be positively addicting. Sure, the Orion Nebula or the Andromeda Galaxy appear grand… and they’ll also look exactly the same throughout the short span of our fleeting human lifetimes. Since the launch of Sputnik in 1957, humans also have added their own ephemeral ‘stars’ to the sky. It’s fun to sleuth out just what these might be, as they photobomb the sky overhead. In the coming week, we’d like to turn your attention towards a unique opportunity to watch a high profile space launch approach a well-known orbiting space laboratory.

On Monday, April 13^th 2015, SpaceX will launch its CRS-6 resupply mission headed towards the International Space Station. As of this writing, the launch is set for 20:33 Universal Time (UT) or 4:33 PM EDT. This is just over three hours prior to local sunset. The launch window to catch the ISS is instantaneous, and Tuesday April 14^th at 4:10 PM EDT is the backup date if the launch does not occur on Monday.

Image credit: Andrew — Dragon chasing the ISS over Ottawa. Image credit and copyright: Andrew Symes

Of course, launches are fun to watch up-close from the Kennedy Space Center. To date, we’ve seen two shuttle launches, one Falcon launch, and the MAVEN and MSL liftoffs headed to Mars from up close, and dozens more from our backyard about 100 miles to the west of KSC. We can typically follow a given night launch right through to fairing and stage one separation with binoculars, and we once even had a serendipitous launch occur during a local school star party! We really get jaded along the Florida Space Coast, where space launches are as common as three day weekend traffic jams elsewhere.

And it’s true that you can actually tell when a launch is headed ISS-ward, as it follows the station up the US eastern seaboard along its steep 52 degree inclination orbit.

On Monday, Dragon launches 23 minutes behind the ISS in its orbit. Viewers up should be able to follow CRS-6 up the U.S. East Coast in the late afternoon sky if it’s clear.

The position of the ISS during Monday’s liftoff, plus the trace for the next two orbits, and the position of the day/night terminator at the end of the second orbit. Image credit: Orbitron

And of course, SpaceX will make another attempt Monday at landing its Falcon Stage 1 engine on a floating sea platform, known as the ‘autonomous spaceport drone ship’ (don’t call it a barge) after liftoff.

About 15-20 minutes after liftoff, Europe and the United Kingdom may catch the Dragon and Falcon S2 booster shortly after the ISS pass on the evening of April 13^th. Observers ‘across the pond’ used to frequently catch sight of the Space Shuttle and the external fuel tank shortly after launch; such a sight is not to be missed!

Spotting Dragon ‘and friends’ on early orbits may provide for a fascinating show in the evenings leading up to capture and berthing. Typically, a Dragon launch generates four objects in orbit: the Dragon spacecraft, the Falcon Stage 2 booster, and the two solar panel covers. These were very prominent to us as they passed over Northern Maine on first orbit in the pre-dawn sky on the morning of January 10^th, 2015. Universe Today science writer Bob King also noted that observers spotted what was probably a venting maneuver over Minnesota on the 2^nd pass on the same date.

Image credit: the launch of CRS-2. — The launch of CRS-2. Image credit: David Dickinson

And even after berthing, the Falcon S2 booster and solar panel covers will stay up in orbit, either following or leading the ISS for several weeks before destructive reentry.

Orbits on Monday and Tuesday leading up to capture for Dragon on Wednesday April 15th at 7:14 AM EDT/11:14 UT will be the key times to sight the pair. Capture by the CanadaArm2 will take place over the central Pacific, and the Dragon will be berthed to the nadir Harmony node of the ISS. Dragon will remain attached to the station until May 17th for a subsequent return to Earth. With the end of the U.S. Space Shuttle program in 2011, SpaceX’s Dragon is currently the only vessel with a ‘down-mass’ cargo capability, handy for returning experiments to Earth.

The first few orbits on the night of the 13^th for North America include a key pass for the US northeast at 1:04UT (on the 14^th)/9:04 PM EDT, and subsequent passes at dusk westward about 90 minutes later. NASA’s Spot the Station App usually lists Dragon passes shortly after launch, as does Heavens-Above and numerous other tracking applications. We’ll also be publishing sighting opportunities for Dragon and the ISS, along with maps on Twitter as @Astroguyz as the info becomes available.

Pre-berthing passes next week favor 40-50 degrees north for evening passes, and 40-50 degrees south for morning viewing.

Dragon/CRS-3 passes over the Netherlands. Image credit: Marco Langbroek

The International Space Station has become a busy place since its completion in 2009. To date, the station has been a port of call for the U.S. Space Shuttles, the Soyuz spacecraft with crews, and Progress, HTV, ATV and Dragon resupply craft.

The current expedition features astronaut Scott Kelly and cosmonaut Mikhail Korniyenko conducting a nearly yearlong stay on the ISS to study the effects that long duration spaceflight has on the human body. Kelley will also break the U.S. duration record by 126 days during his 342 stay aboard the station. The future may see Dragon ferrying crews to the ISS as early as 2017.

And you can always watch the launch live via NASA TV starting at 3:30 PM EDT/19:30 UT.

Don’t miss a chance to catch the drama of the Dragon spacecraft approaching the International Space Station, coming to a sky near you!

April 7, 2015December 23, 2015 by Bob King

Venus and the Pleiades – See the Spectacle!

Venus glides up to the Pleiades or Seven Sisters star cluster this week. This was the view at dusk on April 4. Credit: Bob King

If you’ve ever been impressed by the brilliance of Venus or the pulchritude of the Pleiades, you won’t want to miss what’s happening in the western sky this week. Venus has been inching closer and closer to the star cluster for months. Come Friday and Saturday the two will be only 2.5° apart. What a fantastic sight they’ll make together — the sky’s brightest planet and arguably the most beautiful star cluster side by side at dusk.

No fancy equipment is required for a great view of their close conjunction. The naked eye will do, though I recommend binoculars; a pair of 7 x 35s or 10 x 50s will increase the number of stars you’ll see more than tenfold.

Map showing Venus' path daily from April 6-15, 2015 as it makes a pass at the Pleiades. Created with Chris Marriott's SkyMap — Map showing Venus’ path daily from April 6-15, 2015 as it makes a pass at the Pleiades. The close pairing will make for great photo opportunities . Created with Chris Marriott’s SkyMap

Just step outside between about 8:30 and 10 p.m. local time, face west and let Venus be your guide. At magnitude -4.1, it’s rivaled in brightness only by the Moon and Sun. Early this week, Venus will lie about 5° or three fingers held together at arm’s length below the Pleiades. But each day it snuggles up a little closer until closest approach on Friday. Around that time, you’ll be able to view both in the same binocular field. Outrageously bright Venus makes for a stunning contrast against the delicate pinpoint beauty of the star cluster.

Venus on April 3, 2012, when it last passed over the Seven Sisters cluster. Credit: Bob King — Venus on April 3, 2012, when it last passed right in front of the Seven Sisters. The Pleiades is a young cluster dominated by hot, blue-white stars located 444 light years from Earth. Credit: Bob King

Every 8 years on mid-April evenings, Venus skirts the Pleiades just as it’s doing this week. Think back to April 2007 and you might remember a similar passage; a repeat will happen in April 2023. Venus’ cyclical visits to the Seven Sisters occur because the planet’s motion relative to the Sun repeats every 8 years as seen from Earth’s skies. No matter where and when you see Venus – morning or evening, high or low – you’ll see it in nearly the same place 8 years from that date.

But this is where it gets interesting. On closer inspection, we soon learn that not every Venus-Pleiades passage is an exact copy. There are actually 3 varieties:

* Close: Venus passes squarely in front of the cluster
* Mid-distance: Venus passes ~2.5° from the cluster
* Far: Venus passes ~3.5° from the cluster

The three flavors of varieties of Venus-Pleiades conjunctions. Created with Stellarium — The three varieties of Venus-Pleiades conjunctions . Created with Stellarium

And get this — each has its own 8-year cycle. This week’s event is part of a series of mid-distance passages that recurs every 8 years. Venus last passed directly through Pleiades in April 2012 and will again in April 2020. The next most distant meeting (3.5°) happens in April 2018 and will again in 2026.

Venus circles between Earth and the Sun, causing it to go through phases just like the Moon. The planet is currently in gibbous phase as seen through a small telescope. Credit: Wikipedia with additions by the author — Venus circles between Earth and the Sun and experiences phases just like the Moon from our perspective. The planet is currently in gibbous phase. It reaches its greatest apparent distance from the Sun on June 6 and inferior conjunction on August 15. Credit: Wikipedia with additions by the author

Why three flavors? Venus’ orbit is tipped 3.4° to the plane of the ecliptic or the Sun-Earth line. During each of it 8-year close passages, it’s furthest north of the ecliptic and crosses within the Pleiades, which by good fortune lie about 4° north of the ecliptic. During the other two cycles, Venus lies closer to the ecliptic and misses the cluster by a few degrees.

Fascinating that a few simple orbital quirks allow for an ever-changing variety of paths for Venus to take around (and through!) one of our favorite star clusters.

April 7, 2015December 23, 2015 by David Dickinson

Was This Past Weekend’s Lunar Eclipse Really Total?

Totality... or not? Image credit and copyright: Héctor Barrios

Millions of viewers across the western United States and across the Pacific, to include Australia and New Zealand were treated to a fine Easter weekend lunar eclipse on Saturday. And while this was the third of the ongoing tetrad of four lunar eclipses, it was definitely worth getting up early for and witnessing firsthand.

But was it truly total at all?

To Recap: The April 4th eclipse featured the shortest advertised duration for totality for the 21^st century, clocking in at just four minutes and 43 seconds in length. In fact, you’d have to go all the way back to 1529 to find a shorter span of totality, at one minute and 42 seconds. And you’ll have to wait until September 11^th, 2155 to find one that tops it in terms of brevity.

The April 4th lunar eclipse over the Las Vegas strip. Image credit and copyright: John Lybrand

We wrote recently about the saros cycle, and how this past weekend’s eclipse was the first in lunar saros series 132 to feature totality.

A fascinating discussion as to whether this was a de facto total lunar eclipse has recently sprung up on the message boards and a recent Sky and Telescope article online.

The geometry that creates a total lunar eclipse. Credit: NASA

It all has to do with how you gauge the shape and size of the Earth’s shadow.

This is a surprisingly complex affair, as the Earth’s atmosphere gives the umbra a ragged and indistinct edge. If you’ve ever taken our challenge to determine your longitude using a lunar eclipse — just as mariners such as Christopher Columbus did while at sea — then you know how tough it is to get precise contact timings. There has been an ongoing effort over the years to model the size changes in Earth’s shadow using crater contact times during a lunar eclipse.

Many observers have commented in forums and social media that the northern limb of the Moon stayed pretty bright throughout the brief stretch of totality for Saturday’s eclipse.

What happens (in the skies over) Vegas... the lunar eclipse captured from the Luxor Hotel. Image credit and copyright: Rob Sparks — What happens (in the skies over) Vegas… the lunar eclipse captured from the Luxor Hotel. Image credit and copyright: Rob Sparks

“There are 3 ways of computing the magnitude of a lunar eclipse,” Eclipse expert David Herald mentioned in a recent Solar Eclipse Message List (SEML) posting:

The ‘traditional’ way as used in the Astronomical Almanac is attributed to Chauvenet – where the umbral radius is increased by a simple 2% – with the radius being based on the Earth’s radius at 45 deg latitude (and otherwise the oblateness of the Earth is ignored). For this eclipse the Chauvenet magnitude was 1.005.

The second way (used in the French Almanac, and more recently by Espenak & Meeus in their ‘Five Millennium Canon of Lunar Eclipses’ is the Danjon method. It similarly uses the Earth’s radius at 45 deg (and otherwise the oblateness is ignored), and increases the Earth’s radius by 75km. For this eclipse the Danjon magnitude is 1.001

The most recent approach (Herald & Sinnott JBAA 124-5 pgs 247-253, 2014) is based on the Danjon approach; however it treats the Earth as oblate, allows for the varying inclination of the Earth relative to the Sun during the year, and increases the Earth’s radius by 87km – being the best fit to 22,539 observations made between 1842 and 2011. For this eclipse the magnitude is computed as 1.002.

“As for eclipses, to me it is total when sliver of light comes through the edge of the Earth’s profile,” eclipse chaser Patrick Poitevin told Universe Today. “Once a minimum of light passes through any of the lunar dales (as it does during a total solar eclipse) I do not concede it as a total. Same for a lunar eclipse.”

A partial phase for the April 4th lunar eclipse above a silo. Image credit and copyright: Brian who is called Brian

Michael Zeiler at the Great American Eclipse also had this to say to Universe Today about the subject:

This is a complex question because the shape of the Earth’s umbra upon the Moon is diffuse due to the effects of the Earth’s atmosphere. The various models used (with corrected radii for the Earth) are empirically based on crater timings of past lunar eclipses, of which there is some uncertainty. I’m sure this accounted for the difference between the USNO duration of eclipse and NASA.

The comment (in the recent Sky & Telescope post online) by Curt Renz is valid; correcting for the Earth’s flattening (meaning that the Earth’s radius from pole to pole is about a third of a percent shorter than the radius across the equator) might influence whether this very low magnitude eclipse is total or not. I haven’t made the calculation whether the Earth’s flattening tips this eclipse from total to partial, but it’s plausible.

Totality! Image credit and copyright: Rolf Wahl Olsen

There is another wrinkle: due to parallactic shifts of the Moon when observing from either pole of the Earth, it might be that for a lunar eclipse right on the knife edge of total/partial, that it may indeed be total from one polar region and partial from another. This is a kind of libration, but it would be a very subtle difference and probably unobservable.

It is only possible to conclusively define Saturday’s eclipse as total or partial if you define a brightness threshold for the Sun’s photosphere illuminating an edge of the Moon. The problem here is that this line is indistinct and fuzzy. I watched the lunar eclipse carefully with this question in mind and I could not decide for myself whether this lunar eclipse was total or partial. I think it would require a photometer to make this distinction.

Certainly, there’s little record of just how the 102 second long lunar eclipse of 1529 appeared. Ironically, it too was a total eclipse near sunrise as seen from Europe. On the other side of the coin, the deep partial eclipse of August 26^th, 1961 just missed totality at 98.6% obscuration… and the two lunar eclipses in 2021 have similar circumstances, with a barely total lunar eclipse just 15 minutes long on May 26^th and a 97.4% partial lunar eclipse on November 19^th.

The circumstances for the 1529 total solar eclipse. Image credit: F.Espenak/NASA/GSFC

So maybe we won’t have to wait until 2155 to see another brief lunar eclipse that blurs the lines and refuses to play by the rules.

The eclipse as seen from Coral Towers Observatory. Image credit and copyright: Joseph Brimacombe

What do you, the readers think? What did you see last Saturday morn, a bright total lunar eclipse, or a deep partial?

April 7, 2015December 23, 2015 by Matt Williams

There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

Rima Ariadaeus as photographed from Apollo 10. The crater to the south of the rille in the left half of the image is Silberschlag. The dark patch at the top right is the floor of the crater Boscovich. Credit: NASA

Every year since 1970, astronomers, geologists, geophysicists, and a host of other specialists have come together to participate in the Lunar and Planetary Science Conference (LPCS). Jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA’s Johnson Space Center (JSC), this annual event is a chance for scientists from all around the world to share and present the latest planetary research concerning Earth’s only moon.

This year, one of the biggest attention-grabbers was the findings presented on Tuesday, March 17th by a team of students from Purdue University. Led by a graduate student from the university’s Department of Earth, Atmospheric and Planetary Sciences, the study they shared indicates that there may be stable lava tubes on the moon, ones large enough to house entire cities.

In addition to being a target for future geological and geophysical studies, the existence of these tubes could also be a boon for future human space exploration. Basically, they argued, such large, stable underground tunnels could provide a home for human settlements, shielding them from harmful cosmic radiation and extremes in temperature.

The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed (NASA/JAXA) — *The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA*

Lava tubes are natural conduits formed by flowing lava that is moving beneath the surface as a result of a volcanic eruption. As the lava moves, the outer edges of it cools, forming a hardened, channel-like crust which is left behind once the lava flow stops. For some time, Lunar scientists have been speculating as to whether or not lava flows happen on the Moon, as evidenced by the presence of sinuous rilles on the surface.

Sinuous rilles are narrow depressions in the lunar surface that resemble channels, and have a curved paths that meanders across the landscape like a river valley. It is currently believed that these rilles are the remains of collapsed lava tubes or extinct lava flows, which is backed up by the fact they usually begin at the site of an extinct volcano.

Those that have been observed on the Moon in the past range in size of up to 10 kilometers in width and hundreds of kilometers in length. At that size, the existence of a stable tube – i.e. one which had not collapsed to form a sinuous rille – would be large enough to accommodate a major city.

For the sake of their study, the Purdue team explored whether lava tubes of the same scale could exist underground. What they found was that the stability of a lava tube depended on a number of variables- including width, roof thickness and the stress state of the cooled lava. he researchers also modeled lava tubes with walls created by lava placed in one thick layer and with lava placed in many thin layers.

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. (Purdue University/courtesy of David Blair) — *The inside of a theoretical lunar lava tube, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair*

David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.

“Our work is somewhat unique in that we’ve combined the talents of people from various Departments at Purdue,” Blair told Universe Today via email. “With guidance from Prof. Bobet (a civil engineering professor) we’ve been able to incorporate a modern understanding of rock mechanics into our computer models of lava tubes to see how they might actually fail and break under lunar gravity.”

For the sake of their research, the team constructed a number of models of lava tubes of different sizes and with different roof thicknesses to test for stability. This consisted of them checking each model to see if it predicted failure anywhere in the lava tube’s roof.

“What we found was surprising,” Blair continued, “in that much larger lava tubes are theoretically possible than what was previously thought. Even with a roof only a few meters thick, lava tubes a kilometer wide may be able to stay standing. The reason why, though, is a little less surprising. The last work we could find on the subject is from the Apollo era, and used a much simpler approximation of lava tube shape – a flat beam for a roof.

Mons Rümker rise on the Oceanus Procellarum was taken from the Apollo 15 while in lunar orbit. — *Mons Rümker, an extinct volcanic formation on the Moon’s surface, as imaged by the Apollo 15 spacecraft while in orbit. Credit: NASA*

The study he refers to, “On the origin of lunar sinuous rilles“, was published in 1969 in the journal Modern Geology. In it, professors Greeley, Oberbeck and Quaide advanced the argument that sinuous rilles formation was tied to the collapse of lava flow tubes, and that stable ones might still exist. Calculating for a flat-beam roof, their work found a maximum lava tube size of just under 400 m.

“Our models use a geometry more similar to what’s seen in lava tubes on Earth,” Blair said, “a sort of half-elliptical shape with an arched roof. The fact that an arched roof lets a larger lava tube stay standing makes sense: humans have known since antiquity that arched roofs allow tunnels or bridges to stay standing with wider spans.”

The Purdue study also builds on previous studies conducted by JAXA and NASA where images of “skylights” on the Moon – i.e. holes in the lunar surface – confirmed the presence of caverns at least a few tens of meters across. The data from NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) – which showed big variations in the thickness of the Moon’s crust is still being interpreted, but could also be an indication of large subsurface recesses.

As a result, Blair is confident that their work opens up new and feasible explanations for many different types of observations that have been made before. Previously, it was unfathomable that large, stable caverns could exist on the Moon. But thanks to his team’s theoretical study, it is now known that under the proper conditions, it is least possible.

The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic — *NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) mission calculated the thickness of the moon’s crust. Credit: NASA/JPL-Caltech/S. Miljkovic*

Another exciting aspect that this work is the implications it offers for future exploration and even colonization on the Moon. Already, the issue of protection against radiation is a big one. Given that the Moon has no atmosphere, colonists and agricultural operations will have no natural shielding from cosmic rays.

“Geologically stable lava tubes would absolutely be a boon to human space exploration,” Blair commented. “A cavern like that could be a really ideal place for building a lunar base, and generally for supporting a sustained human presence on the Moon. By going below the surface even a few meters, you suddenly mitigate a lot of the problems with trying to inhabit the lunar surface.”

Basically, in addition to protecting against radiation, a subsurface base would sidestep the problems of micrometeorites and the extreme changes in temperature that are common on the lunar surface. What’s more, stable, subsurface lava tubes could also make the task of pressurizing a base for human habitation easier.

“People have studied and talked about all of these things before,” Blair added, “but our work shows that those kinds of opportunities could potentially exist – now we just have to find them. Humans have been living in caves since the beginning, and it might make sense on the Moon, too!”

In addition to Melosh, Blair and Bobet, team members include Loic Chappaz and Rohan Sood, graduate students in the School of Aeronautics and Astronautics; Kathleen Howell, Purdue’s Hsu Lo Professor of Aeronautical and Astronautical Engineering; Andy M. Freed, an associate professor of earth, atmospheric and planetary sciences; and Colleen Milbury, a postdoctoral research associate in the Department of Earth, Atmospheric and Planetary Sciences.

Further Reading: Purdue News

April 2, 2015December 23, 2015 by Morgan Rehnberg

Planetary Society: We Can Afford to Orbit Humans at Mars by 2033

Mars! Martian meteorites make their way to Earth after being ejected from Mars by a meteor impact on the Red Planet. Image: NASA/National Space Science Data Center.

Start your clocks. If the Planetary Society gets its wish, humans will be lifting off for the Red Planet eighteen years from now. That’s the conclusion of 70 experts in various fields relating to human spaceflight convened by the well-known planetary science advocacy organization, as announced today. A full report describing their conclusions will be released later this year, but in the mean time, let’s take a look at some of the plan’s basic tenants:

Constrain costs by limiting new technology development
Need to “get on the road” by 2033
An orbital mission first will provide valuable experience and opportunities for science
NASA can afford the mission using funds currently devoted to the ISS
Land a crew by the end of the 2030s
Broad support expected for an orbit-first plan
Need to establish means for industry and international partners to participate

Constraining costs: At the height of the Cold War, NASA spent more than $110 billion in a decade to land twelve men on the surface of the Moon. That kind of outlay simply isn’t going to happen today. In order to enable a crewed Mars mission without seeking a dramatic expansion of the agency’s budget, NASA will need to reuse a lot of technology originally developed for things like the International Space Station (ISS). This will come with a side benefit: technology development can be extremely time-intensive and is frequently the source of program delays. The more repurposed technology used, the less likely the mission is to run over schedule.

A 2033 launch: This seems plausible, but only if NASA maintains focus. Too frequently in the past, human spaceflight programs have faced constant redirection. Think of the transition from Constellation to the extended Shuttle program to the Space Launch System and continuing questions regarding the Asteroid Retrieval Mission. If NASA is going to undertake this mission, it will need to survive the transition between at least three (and as many as six!) presidential administrations. That’s no easy feat.

Science from orbit: There is little doubt that orbiting Mars before attempting a landing would provide valuable experience. This is the exact path tread by the Apollo program to great success. But, what of the Society’s claim that such an orbiting mission would provide valuable science opportunities? That’s a little tougher to gauge. Until the full plan is released later this year, it’s tough to know what they have in mind. Certainly, it would be an invaluable opportunity to study the effects of long-duration spaceflight on humans outside of the protection of the Earth’s magnetic field. But, I’m skeptical of any claim about performing orbital Mars science. Just like with the Asteroid Retrieval Mission, it seems likely that any science could be accomplished at a far lower cost through robotic explorers.

Planetary Society CEO Bill Nye addresses the workshop. Photo Credit: Tushar Dayal for The Planetary Society

Raiding the ISS piggy bank: This is perhaps the most interesting piece of the plan. In the wake of Russia’s announcement that they intend to pull out of the ISS collaboration after 2024, the future of America’s presence in Low Earth Orbit has been in question. The Planetary Society provides one possible answer: by using the funds currently earmarked for maintaining the orbiting laboratory, NASA could execute a crewed trip to Mars without needing a budgetary increase above that which accounts for inflation. This is a big deal because NASA funding is projected to remain flat for the foreseeable future.

Touching down before 2040: Regardless of the scientific case for orbital flights, the real scientific promise of human trip to Mars lies on the surface. Astronauts can cover far more ground and do so far more efficiently than their robotic counterparts, so getting people on the surface has to be the ultimate goal. Is 2040 too ambitious given a 2033 orbital launch? I’m not sure, but it’s certainly more realistic than claims made by SpaceX and Mars One.

Support from the public: We can only hope. I think if it was clear that substantial, legitimate progress was being made towards the clear goal of getting humans to Mars by 2033, the public would tune in. But keeping attention on an 20+ year project is no mean feat. Smaller, intermediate goals, a la the Mercury and Gemini programs, will be vital.

A broad coalition: NASA’s willingness to turn over ISS cargo and crew deliveries to private space companies bodes well for continuing these collaborations in the future. But allowing others to service their already-established outpost and joining with them on what will be the next great exploration project are two different things. Also remaining to be seen: will NASA (at the behest of the US Congress) continue to shun burgeoning space power China? Going to Mars will be tough. Why make it tougher than necessary?

Final thoughts: This is an exciting proposal by an organization with a credible history. Moreover, the list of participants in the recent workshop is impressive. The information released today is just the tip of the iceberg, but it has already got me thinking about what the future might hold. One thought that I can’t get out of my mind, though: is an orbital mission an unnecessary risk? Trips to Mars are measured in months, not days, and would put astronauts at unprecedented risk. Would we be drawing out those risks with an orbital mission without really accomplishing a lot of scientific discovery? We’ll have to wait for more details to truly find out.

April 1, 2015December 23, 2015 by Matt Williams

A Red Moon – NOT a Sign of the Apocalypse!

Composite picture of a dark red Moon during a total lunar eclipse. Credit: NASA/ Johannes Schedler (Panther Observatory)

On most evenings, the Moon will appear as a bright yellow or white color in the night sky. But on occasion, the Moon can turn a beautiful and dramatic red, coppery color. Naturally, there are a number of superstitions associated with this stellar event. But to modern astronomers, a Red Moon is just another fascinating phenomenon that has a scientific explanation.

Since the earliest days of recorded history, the Moon has been believed to have a powerful influence over human and animal behavior. To the Romans, staring at a full Moon was thought to drive a person crazy – hence the term “lunatic”. Farmers in the past would plant their crops “by the moon”, which meant sowing their seeds in accordance with the Moon’s phases in the hopes of getting a better harvest.

So naturally, when the Moon turned red, people became wary. According to various Biblical passages, a Blood Moon was thought to be a bad omen. But of course, the Moon turns red on a semi-regular basis, and the world has yet to drown in fire. So what really accounts for a “Red Moon?” What causes Earth’s only satellite to turn the color of blood?

Ordinarily, the Moon appears as it does because it is reflecting light from the Sun. But on occasion, it will darken and acquire either a golden, copper, or even rusty-red color.

There are few situations that can cause a red Moon. The most common way to see the Moon turn red is when the Moon is low in the sky, just after moonrise or before it’s about to set below the horizon. Just like the Sun, light from the Moon has to pass through a larger amount of atmosphere when it’s down near the horizon, compared to when it’s overhead.

The Earth’s atmosphere can scatter sunlight, and since moonlight is just scattered sunlight, it can scatter that too. Red light can pass through the atmosphere and not get scattered much, while light at the blue end of the spectrum is more easily scattered. When you see a red moon, you’re seeing the red light that wasn’t scattered, but the blue and green light have been scattered away. That’s why the Moon looks red.

The second reason for a red Moon is if there’s some kind of particle in the air. A forest fire or volcanic eruption can fill the air with tiny particles that partially obscure light from the Sun and Moon. Once again, these particles tend to scatter blue and green light away, while permitting red light to pass through more easily. When you see a red moon, high up in the sky, it’s probably because there’s a large amount of dust in the air.

Depiction of the Sun's rays turning the Moon red. Image Credit: NASA/Mars Exploration — *Depiction of the Sun’s rays turning the Moon red. Image Credit: NASA/Mars Exploration*

A third – and dramatic – way to get a red Moon is during a lunar eclipse. This happens when the Moon is full and passes into Earth’s shadow (also known as the umbra), which darkens it. At that point, the Moon is no longer being illuminated by the Sun. However, the red light passing through the Earth’s atmosphere does reach the Moon, and is thus reflected off of it.

For those observing from the ground, the change in color will again be most apparent when the Moon appears low in the night sky, just after moonrise or before it’s about to set below the horizon. Once again, this is because our heavy atmosphere will scatter away the blue/green light and let the red light go straight through.

The reddish light projected on the Moon is much dimmer than the full white sunlight the Moon typically reflects back to us. That’s because the light is indirect and because the red-colored wavelengths are only a part of what makes up the white light from the sun that the Moon usually receives.

In other words, when you see a red Moon, you’re seeing the result of blue and green light that has been scattered away, and the red light remaining.

Path of the Moon through Earth's umbral and penumbral shadows during the Total Lunar Eclipse of April 15, 2014. Image Credit: NASA/Eclipse — *Path of the Moon through Earth’s umbral and penumbral shadows during the Total Lunar Eclipse of April 15, 2014. Image Credit: NASA/Eclipse Website*

And that’s the various ways how we get a Red Moon in the night sky. Needless to say, our ancient forebears were a little nervous about this celestial phenomenon occurrence.

For example, Revelations 6:12/13 says that a Red Moon is a sign of the apocalypse: “When he opened the sixth seal, I looked, and behold, there was a great earthquake, and the sun became black as sackcloth, the full moon became like blood, and the stars of the sky fell to the earth as the fig tree sheds its winter fruit when shaken by a gale.”

But rest assured that if you see one, it’s not the end of the world. The Sun and Moon will rise again. And be sure to check out this Weekly Space Hangout, where the April 4th eclipse is discussed:

We have covered lunar eclipses many times on Universe Today, and often explain the red Moon phenomenon. Here’s another good explanation of the science behind a Red Moon, and why the recent series of lunar eclipses in 2014 and 2015 (known as a tetrad) do not mean anything apocalyptic, and here’s another article about how to see a lunar eclipse. Here’s an article that includes a stunning array of images of the Moon during an eclipse in 2014.

Of course, NASA has some great explanations of the red Moon effect during a lunar eclipse. Here’s another one.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Sources: NASA Science: Lunar Eclipse, NASA: Mars Exploration, Discovery News, NASA: Eclipse Website

March 31, 2015December 23, 2015 by David Dickinson

Seeking Ceres: Following the Brave New World Through 2015

A little world is making big headlines in 2015. NASA’s Dawn spacecraft entered orbit around 1 Ceres on March 6^th, 2015, gaving us the first stunning images of the ~900 kilometre diameter world. But whether you refer to Ceres as a dwarf planet, minor planet, or the king of the asteroid belt, this corner of the solar system’s terra incognita is finally open for exploration. It has been a long time coming, as Ceres has appeared as little more than a wandering, star-like dot in the telescopes of astronomers for over two centuries since discovery.

Untitled — The orbit of 1 Ceres. Credit: NASA/JPL

And the good news is, you can observe Ceres from your backyard if you know exactly where to look for it with binoculars or a small telescope. We’ll admit, we had an ulterior motive on pulling the trigger on this post three months prior to opposition on July 24th, as Dawn will soon be exiting its ‘shadow phase’ and start unveiling the world to us up close. The first science observations for Dawn begin in mid-April.

Ceres spends all of 2015 looping through the constellations of Capricornus, Microscopium and Sagittarius. This places it low to the south for northern hemisphere observers on April 1^st in the early morning sky. Ceres will pass into the evening sky by mid-summer. Ceres orbits the Sun once every 4.6 years in a 10.6 degree inclination path relative to the ecliptic that takes it 2.6 AU to 3 AU from the Sun. The synodic period of Ceres is, on average, 467 days from one opposition to the next.

Shining at magnitude +8, April 1^st finds Ceres near the Capricornus/Sagittarius border. Ceres can reach magnitude +6.7 during a favorable opposition. Note that Ceres is currently only 20 degrees east of the position of Nova Sagittarii 2015 No. 2, currently still shining at 4th magnitude. June 29th and November 25th are also great times to hunt for Ceres in 2015 as it loops less than one degree past the 4^th magnitude star Omega Capricorni.

June 30 — Ceres meets up with Omega Capricorni on June 29th. Credit: Stellarium.

You can nab Ceres by carefully noting its position against the starry background from night to night, either by sketching the suspect field, or photographing the region. Fans of dwarf planets will recall that 1 Ceres and 4 Vesta fit in the same telescopic field of view last summer, and now sit 30 degrees apart. Ceres is now far below the ecliptic plane, but will resume getting occulted by the passing Moon on February 3^rd, 2017.

Left — The Palermo transit instrument used to discover Ceres. From *Della Specola Astronomica* (1792)

Ceres was discovered by Giuseppe Piazzi on the first day of the 19^th century on January 1^st, 1801. Ceres was located on the Aries/Cetus border just seven degrees from Mars during discovery. Piazzi wasn’t even on the hunt for new worlds at the time, but was instead making careful positional measurements of stars with the 7.5 centimetre Palermo Circle transit telescope.

At the time, the discovery of Ceres was thought to provide predictive proof of the Titus-Bode law: here was a new planet, just where this arcane numerical spacing of the planets said it should be. Ceres, however, was soon joined by the likes of Juno, Pallas, Vesta and many more new worldlets, as astronomers soon came to realize that the solar system was not the neat and tidy place that it was imagined to be in the pre-telescopic era.

To date, the Titus-Bode law remains a mathematical curiosity, which fails to hold up to the discovery of brave new exoplanetary systems that we see beyond our own.

The view from Ceres itself would be a fascinating one, as an observer on the Cererian surface would be treated to recurrent solar transits of interior solar system worlds. Mercury would be the most frequent, followed by Venus, which transits the Sun as seen from Ceres 3 times in the 21^st century: August 1^st, 2042, November 19^th, 2058 and February 13^th 2068. Mars actually transits the Sun as seen from Ceres even earlier on June 9^th, 2033. Curiously, we found no transits of the Earth as seen from Ceres during the current millennium from 2000 to 3000 AD!

From Ceres, Jupiter would also appear 1.5’ in diameter near opposition, as opposed to paltry maximum of 50” in size as seen from the Earth. This would be just large enough for Jupiter to exhibit a tiny disk as seen from Ceres with the unaided eye. The four major Galilean moons would be visible as well.

The mysteries of Ceres beckon. Does the world harbor cryovolcanism? Just what are those two high albedo white dots? Are there any undiscovered moons orbiting the tiny world? If a fair amount of surface ice is uncovered, Ceres may soon become a more attractive target for human exploration than Mars.

All great thoughts to ponder, as this stellar speck in the eyepiece of your backyard telescope becomes a brand new world full of exciting possibilities.