An artist's conception of jets protruding from a quasar. Credit: ESO/M. Kornmesser
Understanding the formation of stars and galaxies early in the Universe’s history continues to be somewhat of an enigma, and a new study may have turned our current understanding on its head. A recent survey used archival data from four different telescopes to analyze hundreds of galaxies. The results provided overwhelming evidence that radio jets protruding from a galactic center enhance star formation – a result that directly contradicts current models, where star formation is hindered or even stopped.
All early galaxies consist of intensely luminous cores powered by huge black holes. These so-called active galactic nuclei, or AGN for short, are still the topic of intense study. One specific mechanism astronomers are studying is known as AGN feedback.
“Feedback is the astronomer’s slang term for the way in which an AGN – with its large amount of energy release – influences its host galaxy,” Dr. Zinn, lead researcher on this study, recently told Universe Today. He explained there is both positive feedback, in which the AGN will foster the main activity of the galaxy: star formation, and negative feedback, in which the AGN will hinder or even stop star formation.
Current simulations of galaxy growth invoke strong negative feedback.
“In most cosmological simulations, AGN feedback is used to truncate star formation in the host galaxy,” said Zinn. “This is necessary to prevent the simulated galaxies from becoming too bright/massive.”
Zinn et al. found strong evidence that this is not the case for a large number of early galaxies, claiming that the presence of an AGN actually enhances star formation. In such cases the total star formation rate of a galaxy may be boosted by a factor of 2 – 5.
Furthermore the team showed that positive feedback occurs in radio-luminous AGN. There is strong correlation between the far infrared (indicative of star formation) and the radio.
Now, a correlation between the radio and the far infrared is no stranger to galactic astronomy. Stars form in extremely dusty regions. This dust absorbs the starlight and re-emits it in the far infrared. The stars then die in huge supernova explosions, causing powerful shock-fronts, which accelerate electrons and lead to the emission of strong synchrotron radiation in the radio.
This correlation however is a stranger to AGN studies. The key lies in the radio jets, which penetrate far into the host galaxy itself. A “jet which is launched from the AGN hits the interstellar gas of the host galaxy and thereby induces supersonic shocks and turbulence,” explains Zinn. “This shortens the clumping time of gas so that it can condense into stars much more quick and efficiently.”
This new finding conveys that the exact mechanisms in which AGN interact with their host galaxies is much more complicated than previously thought. Future observations will likely shed a new understanding of the evolution of galaxies.
What's the Most Earth-Like Planet In The Solar System?
Life on Earth got you down? Thinking you’d like to pick up and move to another planet? I’ve got bad news for you. Without protection, there’s no place in the entire Solar System that wouldn’t kill you in few seconds.
You’re looking at scorching temperatures, poisonous atmospheres, crushing gravity, bone chilling cold, a complete lack of oxygen, killer radiation, and more.
The entire Solar System is hostile to life as we know it.
If we had to choose from a range of terrible options, what would be the most Earthlike place in the Solar System?
We would want a world that has a similar gravity, similar atmospheric pressure and composition, protection from radiation, and a comfortable temperature. Just like the Earth.
Let’s look at a few candidates:
The Moon looks good. It’s close and… well, it’s close. It’s an airless world, so you’d need a spacesuit. Low gravity is bad news for your bones, which will lose mass and become brittle. Temperatures range from freezing cold to scorching hot, and there’s no atmosphere or significant magnetic field to protect you from the radiation of space.
While we’re suggesting moons, how about Titan, Saturn’s largest Moon?
It’s only 15% of Earth’s gravity, and the temperatures dip down to minus -179 degrees C; cold enough that it rains liquid methane. Even though the atmosphere is unbreathable, the good news is that the pressure is only a little higher than Earth’s. Which means you wouldn’t need a pressurized spacesuit, just a really, really warm coat.
The gravity of Mars is only 38% the gravity of Earth; and we don’t know what effect a long stay in this gravity would have on the human body. The atmosphere is poisonous carbon dioxide, and the pressure is less than 1% of sea level on Earth. So, you’d better pack a spacesuit. The temperatures can rise as high as a comfortable 35 degrees C, but then plunge down to -143 degrees C at the poles. One big problem with Mars is a total lack of magnetosphere. Radiation from space would be a constant hazard for anyone on the surface of the planet.
Atmosphere of Venus. Credit: ESAPerhaps another planet? How about Venus?
On the surface, it’s right out of the running. The temperature is an oven-like 462 degrees C, with a surface pressure 92 times more than Earth. The atmosphere is almost entirely carbon dioxide, with clouds of sulphuric acid. On the plus side, it has gravity roughly similar to Earth, and a thick atmosphere that would protect you from radiation.
Unfortunately, you’d die faster on the surface of Venus than almost anywhere else in the Solar System.
But… there is a place on Venus that’s downright lovely.
Up in the clouds.
Amazingly, if you rise up through the clouds of Venus to an altitude of 50-60 kilometers, the atmospheric pressure and temperature are the same as on Earth. The atmosphere would still be toxic carbon dioxide, but breathable air would be a “lifting gas” on Venus. You could float around the skies of Venus in a balloon made of breathable air. Stand out on the deck of your Venusian sky city in shorts and a T-shirt, soaking up the sunlight in regular Earth gravity.
Sounds idyllic, right?
So, opinions will vary. Some think Mars is the most Earthlike place in the Solar System, but in my opinion, the clouds of Venus are the place to go.
When too much material tries to come together, everything starts to spin and flatten out. You get an accretion disc. Astronomers find them around newly forming stars, supermassive black holes and many other places in the Universe. Today we’ll talk about what it takes to get an accretion disc, and how they help us understand the objects inside.
And the podcast is also available as a video, as Fraser and Pamela now record Astronomy Cast as part of a Google+ Hangout (usually recorded every Monday at 3 pm Eastern Time):
Artist’s impression of the deep blue planet HD 189733b, based on observations from the Hubble Space Telescope. Credit: NASA/ESA.
Since its discovery in 2005, exoplanet HD 189733b has been one of the most-observed planets orbiting another star, as its size, compact orbit, and proximity to Earth has made it a relatively easy target — as extrasolar planets go. From previous studies, astronomers thought the planet may have an enticing blue-sky atmosphere. Now, further examinations with the Hubble Space Telescope have confirmed this planet really does harbor an azure blue atmosphere, very similar to Earth’s ocean blue color.
But this is no ‘pale blue dot’ ocean world. It is a huge gas giant orbiting very close to its host star. It gets blasted with X-rays from its star — tens of thousands of times stronger than the Earth receives from the Sun — and endures wild temperature swings, reaching scorching temperatures of over 1,000 degrees Celsius. Astronomers say it likely rains glass – sideways — in howling 7,000 kilometer-per-hour winds.
Nope, not a place you’d want to visit.
But the new Hubble observations of its color are the first time an exoplanet’s color has been measured and confirmed. The astronomers measured how much light was reflected off the surface of HD 189733b — a property known as albedo.
“This planet has been studied well in the past, both by ourselves and other teams,” says Frédéric Pont of the University of Exeter, UK, co-author of a new paper. “But measuring its colour is a real first — we can actually imagine what this planet would look like if we were able to look at it directly.”
HD 189733b is a Jupiter-sized extrasolar planet orbiting a yellow dwarf star that is in a binary system called HD 189733 in the constellation of Vulpecula, near the Dumbell Nebula, approximately 62 light years from Earth.
The planet’s blue atmosphere does not come from the reflection of a warm ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light. Earlier observations using different methods have reported evidence for scattering of blue light on the planet, but these most recent Hubble observations give robust confirming evidence, the researchers said.
To make their measurements, the team used Hubble’s Space Telescope Imaging Spectrograph (STIS) to look at the system before, during, and after the planet passed behind its host star as it orbited. As it slipped behind its star, the light reflected from the planet was temporarily blocked from view, and the amount of light observed from the system dropped – not by much, about one part in 10,000 — but this was enough for STIS to determine the albedo.
“We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star,” explains Tom Evans of the University of Oxford, UK, first author of the paper. “From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured.”
Albedo is a measure of how much incident radiation is reflected. The greater the albedo, the greater the amount of light reflected. This value ranges from 0 to 1, with 1 being perfect reflectivity and 0 being a completely black surface. The Earth has an albedo of around 0.4.
According to the team’s paper, HD 189733b has an albedo of 0.4 ± 0.12.
The team says this determination will help in future studies of the atmospheres of other extra solar planets, as well as continuing the studies of one of the most-examined planets orbiting another star.
“It’s difficult to know exactly what causes the colour of a planet’s atmosphere, even for planets in the Solar System,” says Pont [5]. “But these new observations add another piece to the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting a more complete picture of this exotic planet.”
A 10 second exposure of a bright pass of the International Space Station. (Photo by Author).
It’s a question we get all the time.
Watch the sky closely in the dawn or dusk hours, and you’ll likely see a moving “star” or two sliding by. These are satellites, or “artificial moons” placed in low Earth orbit. These shine via reflected sunlight as they pass hundreds of kilometres overhead.
Many folks are unaware that you can see satellites with the naked eye. I always make an effort to watch for these during public star parties and point them out. A bright pass of the International Space Station if often as memorable as anything that can be seen through the eyepiece. But after this revelation, “the question” soon follows- “What satellite is that?”
Welcome to the wonderful and highly addictive world of satellite tracking. Ground observers have been watching the skies since Sputnik 1 and the first satellite launch in October 1957. Armies of dedicated volunteers even participated in tracking the early launches of the Space Age with Operation Moonwatch.
Depiction of the apparent motion of a typical satellite overhead with respect to the observer. (Graphic created by author).
The Internet has offered a wealth of information for satellite hunters. Every time I write about “how to spot the ISS,” someone amazes me with yet another new tracker App that I hadn’t heard of. One of my favorites is still Heavens-Above. It’s strange to think that we’ve been visiting this outstanding website daily for a decade and a half now. Heavens-Above specializes in satellites, and will show you a quick listing of passes for brighter satellites once configured with your location. A nifty “quick check” for possibly resolving a mystery satellite is their link for “Daily Predictions for brighter satellites” Which will generate a list of visible passes by time.
Screenshot of a typical list of bright satellite passes from Heavens-Above filtered by brightness, time and location .
Looking at the time, direction, and brightness of a pass is crucial to satellite identification. No equipment is needed to start the hunt for satellites tonight, just a working set of eyes and information. We sometimes use a set of Canon image-stabilized 15x 45 binoculars to hunt for satellites too faint to see with the naked eye. We’ve seen the “Tool Bag” lost during an ISS EVA a few years back, as well as such “living relics” of the early Space Age as Canada’s first satellite Alloutte-1, and the Vanguards (Yes, they’re STILL up there!) using binocs.
A comparison of typical satellite orbits. (Credit: Cmglee, Geo Swan graphic under a Creative Commons Attribution -Share Alike 3.0 unported license).
The trick to catching fainter satellites such as these is to “ambush” them. You’ll need to note the precise time that the selected satellite is going to pass near a bright star. Clicking on a selected satellite pass in Heavens-Above will give you a local sky chart with a time-marked path. I use a short wave portable AM radio tuned to WWV out of Fort Collins, Colorado for an accurate audible time signal. Just sit back, listen to the radio call out the time, and watch for the satellite to pass through the field of view near the target star.
Another great site for more advanced trackers is CALSky. Like Heavens-Above, CALSky will give you a customized list for satellite passes over your location. One cool extra feature on CALSky is the ability to set alerts for passes of the ISS near bright planets or transiting the Sun or Moon. These are difficult events to capture, but worth it!
The International Space Station transiting the Moon as captured by Mike Weasner from Cassiopeia Observatory in Arizona.
A great deal of what’s up there is space junk in the form of discarded hardware. Many satellites are on looping elliptical orbits, only visible to the naked eye when they are near perigee. Many satellites are located out at geosynchronous or geostationary orbits 35,786 kilometres distant and are invisible to the naked eye all together. These will often show up as streaks in astrophotos. An area notorious for geosynchronous satellites exists near the direction of M42 or Orion Nebula. During certain times of year, satellites can be seen nearby, nodding slowly north to south and back again. Around the March and September equinox seasons, geostationary satellites can be eclipsed by the shadow of the Earth. This can also cause communications difficulties, as many geo-sats also lie sunward as seen from the Earth around these times of year.
Probably one of the simplest satellite trackers for casual users is Space Weather’s Satellite Flybys page. North American users simply need to enter a postal code (worldwide users can track satellites via entering “country-state-city”) and a list of passes for your location is generated.
It’s a basic truism of satellite tracking that “aircraft blink; satellites don’t”. Know, we’re going to present an exception to this rule.
Some satellites will flash rhythmically due to a tumbling motion. This can be pretty dramatic to see. What you’re seeing is an expended booster, a cylinder tumbling due to atmospheric drag end-over-end. Some satellites can flash or flare briefly due to sunlight glinting off of reflective surfaces just right. Hubble, the ISS and the late NanoSail D2 can flare if conditions are just right.
The most dramatic of these are Iridium flares. The Iridium constellation consists of 66 active satellites used for satellite phone coverage in low-Earth orbit. When one of their three refrigerator-sized antennas catch the Sun just right, they can flare up to magnitude -8, or 40 times brighter than Venus. CALSky and Heavens-Above will also predict these events for your location.
Didn’t see a predicted satellite pass? Light pollution or bright twilight skies might be to blame. Keep in mind, passes lower to the horizon also fall prey to atmospheric extinction, as you’re looking through a thicker layer of the air than straight overhead. Some satellites such as the ISS or the USAF’s X-37B spy space plane even periodically boost or modify their orbits, throwing online prediction platforms off for a time.
A screenshot example of TLE’s for the ISS & Tiangong-1 from Celestrak.
I use a free tracking platform created by Sebastian Stoff known as Orbitron. Orbitron lets you set your observing location and tailor your view for what’s currently over head. You can run simulations and even filter for “visual only” passes, another plus. I also like Orbitron’s ability to run as a stand-alone system in the field, sans Internet connection. Just remember, for it to work properly, you’ll need to periodically update the .txt file containing the Two-Line Element (TLE) sets. TLE’s are data element sets that describe the orbital elements of a satellite. Cut and paste TLEs are available from Heavens-Above and Celestrak.
Orbitron screenshot for visible satellites using ‘radar’ mode… there’s lots up there! (Credit: Orbitron).
For serious users, NORAD’s Space-Track is the best site for up-to-date TLEs. Space-Track requires a login and user agreement to access, but is available to satellite spotters and educators as a valuable resource. Space-Track also hosts a table of upcoming reentries, as does the Aerospace Corporation’s Center for Orbital & Reentry Debris Studies.
The SeeSat-L mailing list is also an excellent source of discussion among satellite trackers worldwide. Increasingly, this discussion is also moving over to Twitter, which is ideal for following swiftly evolving action in orbit. @Twisst, created by Jaap Meijers,will even Tweet you prior to an ISS pass!
And there’s always something new or strange in the sky for the observant. Satellites such as those used in the Naval Ocean Surveillance System (NOSS) were launched in groups, and are eerie to watch as they move in formations of 2 or 3 across the sky. These are difficult to catch, and all three of our sightings thus far of a NOSS pair have been surreptitious. And we’ve only had the camera ready to swing into action once to nab a NOSS pair;
A NOSS pair captured by the author. The multi-colored trail to the left of the path is an aircraft. Note a bit of “jitter” at the beginning of the exposure- I had to swing the camera into action quickly!
Another bizarre satellite to catch in action is known as the Cloud-Aerosol LiDAR & Infrared Pathfinder Satellite for Observations, or CALIPSO. Part of the “afternoon A-Train” of sun-synchronous Earth observing satellites, you can catch the green LiDAR flashes of CALIPSO from the ground with careful planning, just as Gregg Hendry did in 2008-2009:
A CALIPSO LiDAR pass imaged by Gregg Hendry in 2008. My Hendry mentions that, “The hollow nature of the spots is likely due to some spherical aberration in the camera lens coupled with imperfect focus, and is not representative of the laser beam’s optical quality.” (Credit: Gregg Hendry, used with permission).
NASA even publishes a prediction table for CALIPSO lidar passes. I wonder how many UFO sightings CALIPSO has generated?
Artist’s depiction of the A-Train constellation of Earth-Observing satellites. (Credit: NASA).
And speaking of photography, it’s easy to catch a bright pass such as the ISS on camera. Shooting a satellite pass with a wide field is similar to shooting star trails; just leave the shutter open for 10-60 seconds with a tripod mounted camera. Modern DSLRs allow you to do several test exposures prior to the pass, to get the ISO, f/stop, and shutter speed calibrated to local sky conditions.
You can even image the ISS through a telescope. Several sophisticated rigs exist to accurately track and image the space station through a scope, or you could use our decidedly low-tech but effective hand-guided method;
And that’s a brief overview of the exciting world of sat-spotting… let us know of your tales of triumph and tragedy as you sleuth out what’s going on overhead!
New Horizons LOng Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon, cleanly separated from Pluto itself. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
The New Horizons spacecraft is still about 880 million kilometers (550 million miles) from Pluto, but on July 1 and 3, 2013, the spacecraft’s LOng Range Reconnaissance Imager (LORRI) was able to detect not only Pluto, but its largest moon, Charon, visible and cleanly separated from Pluto itself. Charon orbits about 19,000 kilometers (12,000 miles) away from Pluto, and seen from New Horizons, that’s only about 0.01 degrees away.
“The image itself might not look very impressive to the untrained eye, but compared to the discovery images of Charon from Earth, these ‘discovery’ images from New Horizons look great!” said New Horizons Project Scientist Hal Weaver. “We’re very excited to see Pluto and Charon as separate objects for the first time from New Horizons.”
The frame on the left in the grouping of images above is an average of six different LORRI images, each taken with an exposure time of 0.1 second. The frame to the right is the same composite image but with Pluto and Charon circled; Pluto is the brighter object near the center and Charon is the fainter object near its 11 o’clock position. The circles also denote the predicted locations of the objects, showing that Charon is where the team expects it to be, relative to Pluto. No other Pluto system objects are seen in these images.
These images are just a hint of what’s to come when New Horizons gets closer to the Pluto system. On July 14, 2015, the spacecraft is scheduled to pass just 12,500 kilometers (7,750 miles) above Pluto’s surface, where LORRI will be able to spot features about the size of a football field.
“We’re excited to have our first pixel on Charon,” said New Horizons Principal Investigator Alan Stern, “but two years from now, near closest approach, we’ll have almost a million pixels on Charon –and I expect we’ll be about a million times happier too!”
ALMA/Spitzer image of a monster star in the process of forming
Even though it comprises over 99% of the mass of the Solar System (with Jupiter taking up most of the rest) our Sun is, in terms of the entire Milky Way, a fairly average star. There are lots of less massive stars than the Sun out there in the galaxy, as well as some real stellar monsters… and based on new observations from the Atacama Large Millimeter/submillimeter Array, there’s about to be one more.
Early science observations with ALMA have provided astronomers with the best view yet of a monster star in the process of forming within a dark cloud of dust and gas. Located 11,000 light-years away, Spitzer Dark Cloud 335.579-0.292 is a stellar womb containing over 500 times the mass of the Sun — and it’s still growing. Inside this cloud is an embryonic star hungrily feeding on inwardly-flowing material, and when it’s born it’s expected to be at least 100 times the mass of our Sun… a true stellar monster.
The location of SDC 335.579-0.292 in the southern constellation of Norma (ESO, IAU and Sky & Telescope)
The star-forming region is the largest ever found in our galaxy.
“The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud,” said Nicolas Peretto of CEA/AIM Paris-Saclay, France, and Cardiff University, UK. “We wanted to see how monster stars form and grow, and we certainly achieved our aim! One of the sources we have found is an absolute giant — the largest protostellar core ever spotted in the Milky Way.”
SDC 335.579-0.292 had already been identified with NASA’s Spitzer and ESA’s Herschel space telescopes, but it took the unique sensitivity of ALMA to observe in detail both the amount of dust present and the motion of the gas within the dark cloud, revealing the massive embryonic star inside.
“Not only are these stars rare, but their birth is extremely rapid and their childhood is short, so finding such a massive object so early in its evolution is a spectacular result.”
– Team member Gary Fuller, University of Manchester, UK
The image above, a combination of data acquired by both Spitzer and ALMA (see below for separate images) shows tendrils of infalling material flowing toward a bright center where the huge protostar is located. These observations show how such massive stars form — through a steady collapse of the entire cloud, rather than through fragmented clustering.
SDC 335.579-0.292 seen in different wavelengths of light.
“Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its center,” said Peretto. “This object is expected to form a star that is up to 100 times more massive than the Sun. Only about one in ten thousand of all the stars in the Milky Way reach that kind of mass!”
(Although, with at least 200 billion stars in the galaxy, that means there are still 20 million such giants roaming around out there!)
IBEX observations of spectral slope, where red and yellow indicate lower energy particles and green and blue higher energy ones. The central portion (circle) is looking down the heliotail and shows two lower energy “lobes” on the port and starboard sides and high energy regions at higher northern and southern latitudes.
Figure taken from McComas et al. , Astrophysical Journal, 2013.
Our Solar System is moving through interstellar space and scientists have long thought that the “bubble” around our Solar System – called the heliosphere – might have a tail, similar to how a comet has a tail or how other stars have astrospheres. But that has all been conjecture…. until now.
The IBEX spacecraft (Interstellar Boundary Explorer) has now seen the tail and has mapped out its structure. IBEX scientists were surprised to see the tail has twists and turns, with four separate “lobes,” making it appear somewhat like a four-leaf clover. This downwind region of the heliosphere is called the heliotail.
“Scientists have always presumed that the heliosphere had a tail,” said Eric Christian, IBEX mission scientist, speaking during a Google+ Hangout announcing the new findings. “But this is actually the first real data that we have to give us the shape of the tail.”
IBEX measures the neutral particles created by collisions at the solar system’s boundaries. This technique, called energetic neutral atom imaging, relies on the fact that the paths of neutral particles are not affected by the solar magnetic field. Instead, the particles travel in a straight line from collision to IBEX. Consequently, observing where the neutral particles came from describes what is going on in these distant regions.
“By collecting these energetic neutral atoms, IBEX provides maps of the original charged particles,” said David McComas, lead author on the team’s paper and principal investigator for IBEX at Southwest Research Institute. “The structures in the heliotail are invisible to our eyes, but we can use this trick to remotely image the outermost regions of our heliosphere.”
What they found was unexpected, McComas said.
“By very carefully assembling the statistical observations from the first three years of IBEX data we’ve been able to fill in what we couldn’t see before,” McComas said during the Hangout, “and what we found was that the heliotail was a much larger structure with a much more interesting configuration.
What they found was a tail that appears to have a combination of fast and slow moving particles. There are two lobes of slower particles on the sides, with faster particles above and below. The entire structure is twisted from the pushing and pulling of magnetic fields outside the solar system. McComas likened it to a how a beach ball might twist around if it was attached to a bungee cord.
The IBEX scientists speaking during the Hangout today said this new information will help us understand what the Voyager spacecraft may encounter as they reach the edge of our Solar System.
“IBEX and Voyager are incredibly complimentary missions,” said Christian. “I’ve often said that IBEX is like an MRI, where it can take an image to understand the big picture of what is going on, where the Voyagers are like biopsies, where we can see what is going on in the local area.”
This was the first time a NASA used a Google+ Hangout to broadcast a press briefing. You can watch the full Hangout below:
You can read David McComas’ blog post on the new findings here, and NASA’s press release here.
A thick green arc of aurora settled in for the night last night. It was about 5 degrees thick and some 10 degrees high. A faint but colorful diffuse aurora glowed above it. All photos taken with a 16-35 mm lens at f/2.8 and 30-second time exposure. Credit: Bob King
A burst of energetic particles from the Sun called a coronal mass ejection peppered Earth’s magnetic field yesterday afternoon sparking a modest but beautiful all-night display of the aurora borealis. Another light show may be in the offing tonight for skywatchers living in the northern U.S., Canada and northern Europe.
Around 1 a.m. the arc became more active, sending up occasional rays that lasted from about a minute before fading away and being replaced by another. Credit: Bob King
Pale green fingers of light splayed across the northern sky at twilight’s end came as a surprise. NOAA space weather forecasters had predicted little activity. These soon faded but a thick, fuzzy arc persisted throughout the night. It arched from horizon to horizon across the northern sky like a pallid, monochromatic rainbow. Such arcs are common. Often the aurora never gets past this stage and simmers quietly or even fades away during the night.
Not this one. Around local midnight (1 a.m. CDT) here in Duluth, Minn. small bright spots and a series of tall, faint rays punctuated the arc and over the span of a half-hour completely reshaped it into loopy rayed arcs resembling a crown.
I wasn’t alone when the northern lights peaked about 1:20-2 a.m. At upper left you’ll see the trails of a couple of fireflies. Credit: Bob King
To the eye, the brightest parts of the aurora appeared green, but the taffy-stretched rays were colorless. The camera’s sensitivity coupled with a 30-second time exposure revealed striking pinks and hints of blue. Both pink and green colors are caused by the emission of light from oxygen atoms.
An especially beautiful ray sticks up above the arc. Shorter exposures coupled with shorter shutter speeds are the best way to capture fine details of a northern lights display. Credit: Bob King
Bombarded by high-speed solar wind electrons and protons, they get jazzed into higher energy states. When the atoms return to rest, each spits out a photon of green or red light. All those tiny flashes add up. Multiplied by the billions of atoms that exist even in the rarefied air at the aurora’s typical 60-150 mile (100-250 km) altitude and you get heavenly eye candy.
When we see an auroral arc – and associated rays – we really seeing a small section of the much larger, permanent aurora called the auroral oval. The northern oval is centered over the geomagnetic north pole located in northern Canada. Credit: NASA
I started watching the northern lights at 11 from home then took a drive to darker skies. Even at dawn’s 3 a.m. start, the green arc held its own shot through with rays that occasionally towered halfway up the northern sky. While this display wasn’t a grand spectacle like some auroras, it possessed a certain majesty the same way a long, slow movement concludes a great symphony.
Chances for more of the same continues through tonight and possibly into tomorrow, so keep a watch on the northern sky before you hit the hay tonight. If you see something green and glowing it you might be in for a treat.
In another installment, I’ll share tips on how best to see the northern lights and share several excellent tools you can use for predicting when they might occur.
The Milky Way and airglow seen in the Dark Sky Alqueva Reserve in Portugal. Credit and copyright: Miguel Claro.
Look closely at this beautiful serene view taken by Miguel Claro from Portugal. Not only is it a stunning view of the skies over Lake Alqueva in the Dark Sky Alqueva Reserve in Portugal, but there are also several scientifically interesting features here. Of course, visible is the arc of the Milky Way, filled with colors and light. Seen here is the most central region of the Milky Way, located near the constellations of Scorpio and Sagittarius, where you might recognize many deep sky objects like the Lagoon Nebula (M8) and the Trifid Nebula (M20).
The “glow” seen here is not the aurora borealis, but instead it is airglow (atmospheric chemiluminescence), which is a photochemical reaction that occurs high in the atmosphere when various atoms get excited from the ultraviolet radiation from the Sun. Miguel explained via email that the yellow light is from emissions from sodium atoms in a layer at 92 km, and above it, is green light from oxygen atoms in a layer 90-100 km high. This emission layer is clearly visible from earth orbit, which we’ve seen in many images and videos taken from the ISS.
An annotated version of the Milky Way and airglow seen in the Dark Sky Alqueva Reserve in Portugal. Credit and copyright: Miguel Claro.
“Reflected in the peaceful lake and due to the polarization effect of water, we could clearly see the entire constellation of Scorpius with the real color of each star naturally saturated,” Miguel said via email, “due to this polarization and blurred effect, caused by the slowly movement of water during the long exposure. The orange color of the Red Supergiant Antares could be easily distinguished from the blue color of the Subgiant star, Shaula, in the end of tail.”
Miguel used a Canon 60Da – ISO 1600; 35mm lens at f/2; Exp. 15 secs. Mosaic of 23 images, taken on June 15, at 02:35 AM.
