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. 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 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 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 2012and 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 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.
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 21st 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 11th, 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
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 Telescopearticle 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
“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.
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 26th, 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 26th and a 97.4% partial lunar eclipse on November 19th.
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?
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. 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 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 theApolloera, and used a much simpler approximation of lava tube shape – a flat beam for a roof.
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.
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.
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.
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
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 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:
A little world is making big headlines in 2015. NASA’s Dawn spacecraft entered orbit around 1 Ceres on March 6th, 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.
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 1st 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.
Ceres, Vesta and Mars group together in 2014. Image credit and copyright: Mary Spicer
Shining at magnitude +8, April 1st 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 4th magnitude star Omega Capricorni.
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 3rd, 2017.
Ceres was discovered by Giuseppe Piazzi on the first day of the 19th century on January 1st, 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.
A 1802 publication by Piazzi describing his discovery of Ceres. Credit: Image in the Public Domain.
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.
Piazzi’s 1801 log describing the motion of Ceres against the starry background. Credit: Monatliche Correspondenz
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 21st century: August 1st, 2042, November 19th, 2058 and February 13th 2068. Mars actually transits the Sun as seen from Ceres even earlier on June 9th, 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.
The phases of a total lunar eclipse. Credit: Keith Burns / NASA
Get ready for one awesome total lunar eclipse early Saturday morning April 4th. For the third time in less than a year, the Moon dips into Earth’s shadow, its dazzling white globe turning sunset red right before your eyes. All eclipses are not-to-miss events, but Saturday’s totality will be the shortest in a century. Brief but beautiful – just like life. Read on to find out how to make the most of it.
Four total lunar eclipses in succession with no partials in between is called a tetrad. The April 4th eclipse is part of a tetrad that started last April and will wrap up on September 28. During the 21st century there will be eight sets of tetrads. Credit: NASA
Lunar eclipses don’t usually happen in any particular order. A partial eclipse is followed by a total is followed by a penumbral and so on. Instead, we’re in the middle of a tetrad, four total eclipses in a row with no partials in between. The final one happens on September 28. Even more remarkable, part or all of them are visible from the U.S. Tetrads will be fairly common in the 21st century with eight in all. We’re lucky — between 1600 and 1900 there were none! For an excellent primer on the topic check out fellow Universe Today writer David Dickinson’s “The Science Behind the Blood Moon Tetrad“.
The partially eclipsed Moon on October 8, 2015. For skywatchers across the eastern half of North America, this is about how the Moon will appear shortly before it sets. Those living further west will see totality. Credit: Bob King
Lots of people have taken to calling the tetrad eclipses Blood Moons, referring to the coppery color of lunar disk when steeped in Earth’s shadow and the timing of both April events on the Jewish Passover. Me? I prefer Bacon-and-Eggs Moon. For many of us, the eclipse runs right up till sunrise with the Moon setting in bright twilight around 6:30 a.m. What better time to enjoy a celebratory breakfast with friends after packing away your gear?
Map showing where the April 4 lunar eclipse will be penumbral, partial and total. World map shown in inset. Credit: Larry Koehn / shadowandsubstance.com Inset: Fred Espenak
But seriously, Saturday morning’s eclipse will prove challenging for some. While observers in far western North America, Hawaii, Japan, New Zealand and Australia will witness the entire event, those in the mountain states will see the Moon set while still in totality. Meanwhile, skywatchers in the Midwest and points East will see only the partial phases in a brightening dawn sky. Here are the key times of eclipse events by time zone:
A total lunar eclipse occurs only during full moon phase when the Sun, Earth and Moon lie in a straight line. The Moon slips directly behind Earth into its shadow. The outer part of the shadow or penumbra is a mix of sunlight and shadow and only partially dark. From the inner shadow, called the umbra, the Sun is completely blocked from view. A small amount of sunlight refracted or bent by Earth’s atmosphere into the umbra, spills into the shadow, coloring the eclipsed Moon red.
Eclipse Events EDT CDT MDT PDT
Penumbra eclipse begins
5:01 a.m.
4:01 a.m.
3:01 a.m.
2:01 a.m.
Partial eclipse begins
6:16 a.m.
5:16 a.m.
4:16 a.m.
3:16 a.m.
Total eclipse begins
——–
——–
5:58 a.m.
4:58 a.m.
Greatest eclipse
——–
——–
6:00 a.m.
5:00 a.m.
Total eclipse ends
——–
——–
6:03 a.m.
5:03 a.m.
Partial eclipse ends
———
——–
——–
6:45 a.m.
Penumbra eclipse ends
———
———
——–
——–
* During the penumbral phase, shading won’t be obvious until ~30 minutes before partial eclipse.
Partial eclipse, when the Moon first enters Earth’s dark umbral shadow, begins at 5:16 a.m. CDT near the start of morning twilight. Totality begins at 6:58 a.m. with the Moon already set for the eastern half of the country. Credit: Fred Espenak
This eclipse will also be the shortest total eclipse of the 21st century; our satellite spends just 4 minutes and 43 seconds inside Earth’s umbra or shadow core. That’s only as long as a typical solar eclipse totality. Ah, the irony.
Better have your camera ready or you’ll miss it. The maps below show the maximum amount of the Moon visible shortly before setting from two eastern U.S. cities and the height of the totally eclipsed Moon from two western locations. Click each panel for more details about local circumstances.
The Earth’s shadow will take only a small bite out of the Moon before sunrise (6:47 a.m.) as seen from Washington D.C. From all mainland U.S. locations Virgo’s brightest star Spica will appear about 10° to the left of the Moon. Source: StellariumHere’s the view from Chicago where sunrise occurs at 6:27 a.m. Source: StellariumTotality will be visible From Denver, Colorado with the Moon low in the western sky in morning twilight. Sunrise is 6:42 a.m. Source: StellariumSeattle and the West Coast get a great view of totality in a dark sky. The final partial phases will also be visible. Sunrise there is 6:40 a.m. Source: Stellarium
Now that you know times and shadow coverage, let’s talk about the fun part — what to look for as the event unfolds. You’ll need to find a location in advance with a good view to the southwest as most of the action happens in that direction. Once that detail’s taken care of and assuming clear weather, you can kick back in a folding chair or with your back propped against a hillside and enjoy.
During the early partial phases you may not see the shadowed portion of the Moon with the naked eye. Binoculars and telescopes will show it plainly. But once the Moon is about 50% covered, the reddish-orange tint of the shadowed half becomes obvious. During total eclipse (right), the color is intense. Credit: Jim Schaff
The entire eclipse can be enjoyed without any optical aid, though I recommend a look through binoculars now and then. The eclipsed Moon appears distinctly three-dimensional with only the slightest magnification, hanging there like an ornament among the stars. The Earth’s shadow appears to advance over the Moon, but the opposite is true; the Moon’s eastward orbital motion carries it deeper and deeper into the umbra.
Nibble by nibble the sunlit Moon falls into shadow. By the time it’s been reduced to half, the shaded portion looks distinctly red even to the naked eye. Notice that the shadow is curved. We live on a spherical planet and spheres cast circular shadows. Seeing the globe of Earth projected against the Moon makes the roundness of our home planet palpable.
A simulated view looking back at Earth from the Moon during a total lunar eclipse on Earth. Sunlight grazing Earth’s circumference gets filtered by our atmosphere in exactly the same way the setting or rising Sun looks red. All the cooler colors have been scattered away by air and Red light, bent into the umbra by atmospheric refraction, bathes the lunar surface in red. As you might have guessed, when we see a total lunar eclipse on Earth, lunar inhabitants see a total eclipse of the Sun by Earth. Source: Stellarium
When totality arrives, the entire lunar globe throbs with orange, copper or rusty red. These sumptuous hues originate from sunlight filtered and bent by Earth’s atmosphere into the umbral shadow. Atmospheric particles have removed all the cooler colors, leaving the reds and oranges from a billion sunrises and sunsets occurring around the planet’s circumference. Imagine for a moment standing on the Moon looking back. Above your head would hang the black disk of Earth, nearly four times the size of the Moon in our sky, ringed by a narrow corona of fiery light.
Color varies from one eclipse to the next depending on the amount of water, dust and volcanic ash suspended in Earth’s atmosphere. The December 30, 1982 eclipse was one of the darkest in decades due to a tremendous amount of volcanic dust from the eruption of the Mexican volcano El Chichon earlier that year.
The more particles and haze, the greater the light absorption and darker the Moon. That said, this eclipse should be fairly bright because the Moon does not tread deeply into Earth’s shadow. It’s in for a quick dip of totality and then resumes partial phases.
The Moon’s color can vary from yellow-orange to dark, smoky brown during totality depending on the state of the atmosphere. You can also see lots of stars in the sky right up to the Moon’s edge when it’s in Earth’s shadow. This photo from last April’s eclipse. Spica is below the Moon and Mars to the right. Credit: Bob King
It’s northern edge, located close to the outer fringe of Earth’s umbra, should appear considerably brighter than the southern, which is closer to the center or darkest part of the umbra.
Earth’s shadow exposed! When a lunar eclipse occurs at dusk or dawn we have the rare opportunity to see Earth’s shadow on the distant Moon at the same time it’s visible as a dark purple band cast on the upper atmosphere as seen here on October 8, 2015. Credit: Bob King
Besides the pleasure of seeing the Moon change color, watch for the sky to darken as totality approaches. Eclipses begin with overwhelming moonlight and washed out, star-poor skies. As the Moon goes into hiding, stars return in a breathtaking way over a strangely eerie landscape. Don’t forget to turn around and admire the glorious summer Milky Way rising in the eastern sky.
Lunar eclipses remind us we live in a Solar System made of these beautiful, moving parts that never fail to inspire awe when we look up to notice.
In case you can’t watch the eclipse from your home due to weather or circumstance, our friends at the Virtual Telescope Project and SLOOHwill stream it online.
Solar energy energizes the drama of life on Earth, such as the bird caught transiting the solar disk as seen here. Image credit and copyright: Roger Hutchinson
You can be thankful that we bask in the glow of a relatively placid star. Currently about halfway along its 10 billion year career on the Main Sequence, our Sun fuses hydrogen into helium in a battle against gravitational collapse. This balancing act produces energy via the proton-proton chain process, which in turn, fuels the drama of life on Earth.
Looking out into the universe, we see stars that are much more brash and impulsive, such as red dwarf upstarts unleashing huge planet-sterilizing flares, and massive stars destined to live fast and die young.
Our Sun gives us the unprecedented chance to study a star up close, and our modern day technological society depends on keeping a close watch on what the Sun might do next. But did you know that some of the key mechanisms powering the solar cycle are still not completely understood?
One of the exceptionally active sunspot groups seen for Cycle #24 in early 2014. Image credit: David Dickinson
One such mystery confronting solar dynamics is exactly what drives the periodicity related to the solar cycle. Follow our star with a backyard telescope over a period of years, and you’ll see sunspots ebb and flow in an 11 year period of activity. The dazzling ‘surface’ of the Sun where these spots are embedded is actually the photosphere, and using a small telescope tuned to hydrogen-alpha wavelengths you can pick up prominences in the warmer chromosphere above.
This cycle is actually is 22 years in length (that’s 11 years times two), as the Sun flips polarity each time. A hallmark of the start of each solar cycle is the appearance of sunspots at high solar latitudes, which then move closer to the solar equator as the cycle progresses. You can actually chart this distribution in a butterfly diagram known as a Spörer chart, and this pattern was first recognized by Gustav Spörer in the late 19th century and is known as Spörer’s Law.
The ‘Butterfly diagram’ of sunspot distribution by latitude over previous solar cycles. Image credit: NASA/Marshall Spaceflight Center
We’re currently in the midst of solar cycle #24, and the measurement of solar cycles dates all the way back to 1755. Galileo observed sunspots via projection (the tale that he went blind observing the Sun in apocryphal). We also have Chinese records going back to 364 BC, though historical records of sunspot activity are, well, spotty at best. The infamous Maunder Minimum occurred from 1645 to 1717 just as the age of telescopic astronomy was gaining steam. This dearth of sunspot activity actually led to the idea that sunspots were a mythical creation by astronomers of the time.
But sunspots are a true reality. Spots can grow larger than the Earth, such as sunspot active region 2192, which appeared just before a partial solar eclipse in 2014 and could be seen with the unaided (protected) eye. The Sun is actually a big ball of gas, and the equatorial regions rotate once every 25 days, 9 days faster than the rotational period near the poles. And speaking of which, it is not fully understood why we never see sunspots at the solar poles, which are tipped 7.25 degrees relative to the ecliptic.
Other solar mysteries persist. One amazing fact about our Sun is the true age of the sunlight shining in our living room window. Though it raced from the convective zone and through the photosphere of the Sun at 300,000 km per second and only took 8 minutes to get to your sunbeam-loving cat here on Earth, it took an estimated 10,000 to 170,000 years to escape the solar core where fusion is taking place. This is due to the terrific density at the Sun’s center, over seven times that of gold.
Another amazing fact is that we can actually model the happenings on the farside of the Sun utilizing a new fangled method known as helioseismology.
Another key mystery is why the current solar cycle is so weak… it has even been proposed that solar cycle 25 and 26 might be absent all together. Are there larger solar cycles waiting discovery? Again, we haven’t been watching the Sun close enough for long enough to truly ferret these ‘Grand Cycles’ out.
The sunspot number predicted for the current Cycle #24 versus reality. Image credit: NASA
Are sunspot numbers telling us the whole picture? Sunspot numbers are calculated using formula that includes a visual count of sunspot groups and the individual sunspots in them that are currently facing Earthward, and has long served as the gold standard to gauge solar activity. Research conducted by the University of Michigan in Ann Arbor in 2013 has suggested that the orientation of the heliospheric current sheet might actually provide a better picture as to the goings on of the Sun.
Another major mystery is why the Sun has this 22/11 year cycle of activity in the first place. The differential rotation of the solar interior and convective zone known as the solar tachocline drives the powerful solar dynamo. But why the activity cycle is the exact length that it is is still anyone’s guess. Perhaps the fossil field of the Sun was simply ‘frozen’ in the current cycle as we see it today.
Color us skeptical on these ideas. Although Jupiter accounts for over 70% of the planetary mass in the solar system, it’s 1/1000th as massive as the Sun. The barycenter of Jupiter versus the Sun sits 36,000 kilometres above the solar surface, tugging the Sun at a rate of 12.4 metres per second.
Rigs to view the Sun in both hydrogen-alpha and visible light. Credit: David Dickinson
I suspect this is a case of coincidence: the solar system provides lots of orbital periods of varying lengths, offering up lots of chances for possible mutual occurrences. A similar mathematical curiosity can be seen in Bode’s Law describing the mathematical spacing of the planets, which to date, has no known basis in reality. It appears to be just a neat play on numbers. Roll the cosmic dice long enough, and coincidences will occur. A good test for both ideas would be the discovery of similar relationships in other planetary systems. We can currently detect both starspots and large exoplanets: is there a similar link between stellar activity and exoplanet orbits? Demonstrate it dozens of times over, and a theory could become law.
This spiral galaxy image was taken on glass photographic plate is one in a series of photos taken over decades. From the Harvard Plate collection. Image courtesy American Museum of Natural History.
In the late 19th century, astronomers developed the technique of capturing telescopic images of stars and galaxies on glass photographic plates. This allowed them to study the night sky in detail. Over 500,000 glass plate images taken from 1885 to 1992 are part of the Plate Stacks Collection of the Harvard-Smithsonian Center for Astrophysics (CfA), and is is the largest of its kind in the world.
“The images captured on these plates remain incredibly valuable to science, representing a century of data on stars and galaxies that can never be replaced,” writes astronomer Michael Shara, who is Curator in the Department of Astrophysics at the American Museum of Natural History in New York City, who discussed the plates and their significance in a new episode of AMNH’s video series, “Shelf Life.”
These plates provide a chance to travel back in time, to see how stars and galaxies appeared over the past 130 years, allowing astronomers to do what’s called “time domain astronomy”: studying the changes and variability of objects over time. These include stars, galaxies, and jets from stars or galactic nuclei.
But viewing these plates is difficult. The glass plates can still be viewed on a rather archaic plate viewer—a device that’s like an X-ray light box in a doctor’s office. But those aren’t readily available, and Harvard is hesitant about shipping the 100-plus-year-old glass plates around the world. If astronomers travel to Cambridge to dig through the archives, they can spend hours poring over logbooks or just looking for the right plate. Plus, there’s not an easy way to compare these plates to today’s digital imagery.
AMNH is helping CfA to digitize the glass plates, which is discussed in the video. There’s also a citizen science project called DASCH to help digitize the telescope logbooks record that hold vital information associated with a 100-year-long effort to record images of the sky. By transcribing logbook text to put those historical observations in context, volunteers can help to unlock hidden discoveries.
Find out more about DASCH here, and you can read the news release from last year about it here.
Find out more about AMNH’s digitization project here, where you can also see more episodes of “Shelf Life.”
Past episodes usually focus on the “squishy/hold-in-your-hand side of natural history collections,” said Kendra Snyder from AMNH’s communications department, adding that this latest episode about astronomy offers a different take on what people think is in museum collections.
Short time exposure of the star Sirius with the camera attached to a small telescope. I tapped the tube to make the star bounce around, recording the star's rapid color changes as it twinkled. All photos by the author
We all have cameras, and the sky’s an easy target, so why not have a little fun? Ever since I got my first camera at age 12 I wanted to shoot time exposures of the night sky. That and a tripod are all you need. Presented here for your enjoyment are a few oddball and yet oddly informative images of stars and planets. Take the word “art” loosely!
Colorless mess. This is the companion to the Sirius image and shows Jupiter through the telescope. Notice how blandly white it appears. That’s because Jupiter’s disk is large enough to not show twinkling (and color changes) caused by atmospheric turbulence as in the case of point-like Sirius. Credit: Bob KingPleasing parallels. Orion’s Belt and Sword trail in this time exposure made with a 200mm lens. The fuzzy pink streak is the Orion Nebula. They’re trails are nearly parallel because the stars all lie close to the celestial equator and were crossing the meridian at the time. Credit: Bob KingStar Trek Effect. I centered Jupiter in the viewfinder, pressed the shutter button for a 20-second time exposure and slowly hand-zoomed the lens from 70mm to 200mm. It took a few tries because I was shooting blind, but even the rejects weren’t too bad. Credit: Bob KingColor by Fog. The colors of stars are accentuated when spread into a glowing disk by fog or light cloud. Orion is at right with the crescent moon at lower left. Credit: Bob KingSnow flies. During a time exposure taken on a snowy but partly cloudy night, snowflakes, illuminated by a yard light, streak about beneath a Full Moon earlier this winter. Credit: Bob KingStuttering Stars. For this image of the Big Dipper the camera was on a tracking mount. I left the shutter open for about 25 minutes with the tracking turned off so the stars would trail. Then the lens was covered with a black cloth for a few minutes to create a gap between this exposure and the next. After the cloth was removed, I started the tracking motor and kept the exposure running for a few minutes. A diffusion filter was used in front of the lens to soften and enlarge the brightest stars. Credit: Bob King
