Monday, April 30, 2012

Luna Nova

Today I have a picture of a very young Moon for you to enjoy. The Moon was new on April 20 at 9:18 PM Hawaii Standard Time, and this picture is from April 22 at 7:55 PM, just 46 hours and 37 minutes later. While it's by no means the earliest you can see the new crescent Moon (people have done it less than 24 hours after new, an incredibly difficult feat), it's still a nice thin crescent in this view.

The Moon 46 hours and 37 minutes after new, seen from Mauna Kea.

This shot is actually a collage made of 5 separate images I took using a 14-inch telescope at the Vis, which is why you can see such good detail on the lunar rim. I don't really have much more to say about it tonight, other than that I need to go email it to the visiting tourist who was so intrigued when he saw me taking the images that he requested I send him the finished product, sight unseen.

Thursday, April 26, 2012

More Nebulae! Flames and Horseheads.

Today I have Yet Another Nebula Picture (YANP), this time of two nebulae close enough on the sky to share a field of view. One of the them, the Horsehead Nebula, is probably one of the more distinctive and well-known nebulae out there, while the lesser-known Flame Nebula is a visual treat.

Also, these nebulae are nice because they lie near a prominent feature in the night sky, one that many (if not most) people are familiar with. Take a look at the picture below:

The Flame and Horsehead Nebulae in Orion. Click for a larger version.

See that bright star there? That is Alnitak, and you probably know it better as the left (or eastern) star in Orion's belt. The large bright region to its left is the Flame Nebula. Its bright red glow comes from the hydrogen atoms in the cloud being ionized by Alnitak's intense ultraviolet radiation. Alnitak itself is an O-class star, the hottest and most luminous class of stars, and puts out nearly a million times more light across the electromagnetic spectrum than the Sun does.

Just below Alnitak you can see the prominent outline of the Horsehead Nebula silhouetted against a backdrop of glowing hydrogen. In fact, there's a very nice, nearly straight line where a large dusty cloud blocks the light of the nebula behind it that extends for over half a degree below Alnitak.

What's cool is that this cloud of dust is also responsible for the Flame Nebula's dramatic shape, because the same dust cloud that causes the Horsehead Nebula is also in view in front of the Flame Nebula's backdrop of glowing hydrogen. So in a way, these two nebulae are intimately linked.

Another way to illustrate just how dark and dusty the molecular cloud that's producing these nebulae is, is to note that there is no inherent difference in the density of stars across the picture. The left side of the picture has just as many stars as the right side (you're looking through the plane of the Galaxy, after all); it's only the presence of the dust cloud that's blocking out the light from the ones behind it. (The ones you see on the left are either stars in front of the cloud, or ones seen where it is thinner.) All in all, a very beautiful section of the sky, one with a lot of very young, hot, and luminous stars.

Sunday, April 22, 2012

Eta Carinae Et Nebulae

Today I have a picture of the huge expanse of nebulosity found in the southern constellation Carina, the Keel. The Carina Nebula, as it's known, lies roughly 6,500 to 10,000 light-years away in the Carina-Sagittarius Arm of the Galaxy. It is actually about four times larger than the Orion Nebula, but is much less well-known due to its southerly location.

The Carina Nebula in the constellation Carina, the Keel.
This picture is unfortunately not quite up to my usual standards due to losing tracking between taking the luminance data and the color data, because someone walked in front of the telescope which caused it to lose guiding (the nebula is pretty low on the horizon from Hawaiʻi. Normally my targets are much higher in the sky, so it isn't a problem, which is why I was unprepared for it). Thankfully, I was able to recover fairly well, though it's not quite as focused as usual.

Like the Orion Nebula, the Carina Nebula is a star-forming region, a stellar hatchery if you will. It contains some of the largest and most massive stars known to exist in our galaxy. One of these stars is known as Eta Carinae, and it is actually visible in this image. Below, I have an crop of the center of the image, with a few prominent objects marked in it.

The large circle on the right is a star cluster known as Trumpler 14, the structure in the middle is a dark dusty nebula called the Keyhole Nebula (silhouetted against the glowing hydrogen behind), and the star in the small circle on the left is Eta Carina.

Eta Carina is pretty mysterious as stars go, and there is much we still have yet to learn about it. For starters, it is probably more than one star. Currently it is thought to be two stars, one with a mass of ~100 times that of the Sun, and one with about 30 solar masses. It's hard to say, because back in 1841 it put out a huge cloud of gas and dust that makes it pretty much impossible to see the star itself. This corresponded with a major increase in its luminosity (the amount of energy it puts out). In fact, just two years later, in 1843, Eta Carinae underwent what is known as a supernova impostor event. Basically, it put out as much light as a normal supernova would, but didn't blow up.

How is this possible, you ask? Well, remember how I said Eta Carinae was one of the most massive stars in the Milky Way. Normally, a star only about 8 times more massive than the Sun can go supernova. Eta Carinae, of course, is much, much more massive than that, so it can easily fling out huge amounts of material and still survive. Eta Carinae (or at least the larger component of it) is so large, in fact, that it is in serious danger of blowing itself apart just from its normal energy generation. In a normal star, energy generated by fusing hydrogen to helium is just sufficient to counteract the force of gravity trying to collapse the star. As more mass is added, the force of gravity increases, which increases the rate of energy generation, keeping the star in hydrostatic equilibrium. However, there comes a point where the energy output of the core becomes so great that it can actually start to drive off the outer layers of the star.

This point is known as the Eddington Limit, after Sir Arthur Eddington who first proposed it. It is roughly 32,000 \(\times\) the mass of the star in solar masses, so our Sun would have to be putting out about 32,000 times more energy than it currently does before it would begin to disintegrate under its own power. It doesn't do this because its mass is not sufficient to crush its core hard enough to generate that amount of power. Eta Carina, however, may be big enough to do so (or at least get really, really, close). It's hard to tell, because we don't know for sure just how luminous it is. This theory may help explain why it put out such a huge burst of material back in the 19th century. Or it may be some other, completely unrelated mechanism. The bottom line is, we just don't know yet. That's all just part of the wonder and excitement of studying the universe!

Thursday, April 19, 2012

Climbing Mauna Loa

Last week I had the amazing opportunity to hike the summit of Mauna Loa with a few friends.

Mauna Loa, if you don't know, is the largest volcano on Earth, and second in the Solar System only to Olympus Mons on Mars. It is estimated to have a volume of 18,000 cubic miles of rock (75,000 km³), that is, 375 times the size of Mount Hood, enough to fill the Grand Canyon 18 times over, and more than the entire Sierra Nevada range. It achieves this great volume by being not only incredibly tall (almost 56,000 feet [17 km] from the ocean floor), but incredibly flat. The overall slope of the mountain doesn't exceed 12°, which, despite its great height, makes it rather hard to see when you're directly on it. From Hilo, Mauna Loa just looks like a big hill, while Mauna Kea (which is only 120 feet [36 m] taller than it) looks like a looming mountain. The name Mauna Loa means “Long Mountain” in Hawaiian, and as I quickly discovered, it could not be more appropriate.

We got out of Hilo a bit late, and the fact that the road from the Saddle road up to the Mauna Loa Observatories is a big pot-hole-y mess meant we didn't arrive at the 11,000 foot mark until 8:40 AM, at which point we left the car and began hiking [edit from the future: how funny that by 2017 the road would be entirely paved, and an easier drive than Mauna Kea]. Now, being the over-prepared nerd that I am I had taken the opportunity beforehand to thoroughly inspect our route on Google Earth, so that I would have at the very least a mental map in case I couldn't get reception, or the weather suddenly turned nasty and we couldn't navigate. The smooth slope of Mauna Loa actually makes it somewhat difficult to determine which way is mauka (uphill, away from the sea) or makai (downhill, seaward) in places.

Anyway, on Google Earth there was a very clearly defined route traveling up the mountain via several switch backs that petered out just below the rim of North Pit, a small secondary crater on the edge of the summit caldera, which is named Mokuʻāweoweo.  (Mokuʻāweoweo is an absolutely huge crater, 1.5 miles wide and 3 miles long. North Pit is small only in comparison, and is probably a mile in diameter.) I naturally assumed that this was the “6 mile trail” mentioned on several websites, and that it would be a fairly simple matter to just walk up the nice, gentle slope of Mauna Loa's flank.

Since no one else was showing any signs of navigation, I assumed the position (aided by the fact that I had excellent reception [and access to Google Maps] the entire way up) and bravely led the group up the fork of the trail that led up the mountain, rather than the mysterious fork that appeared to continue on around the mountain. Or, rather, I pointed the way out to the group and huffed and puffed along behind them in the thin atmosphere. Along the way I turned around long enough to snap the following picture of Mauna Loa in the early morning light:

Mauna Kea in all its glory. So pretty...
In the slightly zoomed-in image below, you can make out several observatories on the summit (I see the James Clerk Maxwell Telescope, Subaru, the Caltech Sub-millimeter Observatory, Keck I & II, the Canada-France-Hawaii Telescope, Gemini North, and the UH 88-inch telescope) and can even spot the limits of Mauna Kea's glaciers as a fairly distinct line encircling the mountain about a third of the way down from the summit.

Observatories on Mauna Kea, and the line marking the extent of glaciation.
Breathing at altitude is funny stuff. The slightest exertion leaves you breathing heavily, and heavy exertion has you gasping. By the end of the day I was beginning to worry I'd cracked every rib in my body from the force of my breathing alone. (Thankfully, that healed up in about two day. But boy, when it hurts to breathe, every day seems like an eternity.)

Anyway, we continued on our merry oxygen-deprived way for an hour. Then two. Then another. And another. Finally, after five hours of almost non-stop walking, at long last we we reached the edge of North Pit. Oh, and did I mention that the clouds came in and started dropping sleet on us (yes, sleet) about noon?

Trying to get out of the constant light sleet I clamored down the edge of North Pit, found a slight outcropping of the crater rim, and proceeded to eat the small lunch I had brought with me. It was quite exciting to be sitting on the frozen surface of a vast lava sea, knowing that the volcano had been active a mere twenty-eight years earlier, and that a vast magma chamber lurked only a little less than two miles below my feet. I was able to put together the following panorama while I was sitting there.
Edit (3/17/18): I redid the panorama using Hugin, but you can still see the original by mousing over the image.

This picture was taken in a rare five-minute period when the sun broke through the clouds. Off in the distance, just below the far wall of North Pit you can see steam rising from the floor of the crater. (Probably from rain landing on rocks heated by the sun I hasten to add, not because they were being heated by magma underneath!) Further off you can see through the break in the wall of Mokuʻāweoweo, and even see the highest part of the crater rim near the center of the image.

By this time, it was already 2 in the afternoon, the sleet was switching to rain and back again and showing no signs of letting up, and we still had to walk down, so after eating a woefully late lunch we started the trek back down. I was happy when we got low enough for the sleet to stop, until it was replaced by rain. That morning I had made the decision to wear my (lighter, non-water-proof) fleece in favor of my (heavier, water-proof) coat, so everything I had very slowly began to moisten as we walked down. That actually turned out to be a blessing in disguise, because my damp clothes kept me from overheating and kept my body temperature just about perfect the entire way down. Thankfully the rain never got heavier than a light drizzle.

Three hours after we left the summit we finally staggered back to car, whereupon we had another hour-and-a-half drive back to civilization. I haven't heard of any lasting injuries, but we were all stiff and sore for the next few days.

Mauna Loa is an absolutely fascinating mountain, especially when you compare it with its near sibling Mauna Kea. The lava on Mauna Loa is obviously much newer and fresher than on Mauna Kea, where most lava flows have been covered by either cinder, glacial deposits, or vegetation. (There are some places near Mauna Kea's summit where you can see the exposed flows, usually deeply scarred from the glaciers they erupted under.) On Mauna Loa, lava flows stand out stark and fresh. They also weather to a different color; while old lava on Mauna Kea oxidizes to a reddish-brown color, Mauna Loa's lava goes more for a straight brown. It's very neat to be driving through a patch of black lava, probably less than a hundred years old, and come across a small kīpuka of much older brown lava that didn't get covered in the middle of it. There is a lot of older lava on Mauna Loa (take a look at the picture below for some) and it's fascinating to think about what Mauna Kea must have looked like before it began its post-shield phase and covered everything with a layer of cinder. Alternatively, it's really cool to imagine Mauna Loa after it enters its post-shield phase and starts erupting cinder and cinder cones all over.

A fairly old lava flow on Mauna Loa's flank.
Note how the lava is starting to crumble and flake off.
All in all it was an incredible experience, though one I am in no hurry to replicate. In fact, after we got back and started mentioning it to others more familiar with the mountain, it turned out that we had missed the actual trail and taken the vehicle trail. (Turns out it was that mysterious fork after all.) So instead of a 12.2 mile round trip, it was probably more like 15-20. Because it took us so long to reach the summit we were in no position to actually explore or look around, so we didn't make it to either the true summit on the west side of the crater or the location of the historic Wilkes Expedition campsite on the east side. (The Wilkes Expedition was part of the U.S. Exploring Expedition to the Pacific, a push by the young United States to explore the Pacific for scientific and commercial reasons that lasted from 1838 to 1842. Fun fact: the site of Wilkes' campsite on the rim of Mokuʻāweoweo is the only physical evidence in the Pacific that remains of the entire expedition.)

Now that I know where the trail really is, I wouldn't mind going back some day (hopefully one with better weather) and trying again for the summit. Because despite the discomfort and days of soreness, there's something incredibly cool about standing on an active volcano so far removed from sea level and civilization.

I'm going to close this post by linking to a chapter from a book called Life in Hawaii by Titus Coan, an early American missionary. He describes Mauna Loa's great eruption of 1855-56 that came within a few miles of destroying Hilo. He describes ascending to over 12,000 feet to find the source of the eruption, watching it for many days, trying to cross it in full flood (!!!), and a whole bunch of other incredibly nifty observations about it. It's a long read, but I suspect that once you start you won't be able to stop reading it. Here it is: The Eruption of 1855.

Friday, April 13, 2012

Globular Cluster Photo Series (Part 17): M3

Today I have a picture of one of the biggest and brightest globular clusters in the Northern Hemisphere, narrowly beaten out by the likes of M13. This globular cluster, Messier 3, is found in the northerly constellation of Canes Venatici, the Hunting Dogs, just below the handle of the Big Dipper asterism.

M3 is, as its name indicates, the 3rd object in Messier's popular list of bright non-comets, and as such it may have the distinction of being the object that prompted him to begin a systematic search for these objects instead of simply cataloging ones that he came across by chance.

M3 is a bright cluster that currently stands as the record-holder for largest number of variable stars – 274 – found in a globular cluster to date. It has an angular size on the sky of 18.0 arcminutes, a bit less than two-thirds of the width of the full Moon and ever-so-slightly smaller than M13's 20.0. It is actually a bit larger than M13 physically at 180 light-years across (10 more than M13),  but is also a bit further away from us at 33,900 light-years compared to M13's 25,000. Even this far away from us, further away than the center of our own galaxy, it still shines just bright enough to possibly be seen with the naked eye under pristine conditions at apparent magnitude 6.2. With any sort of magnification, of course, it looks quite nice. (For comparison, the distance to the supermassive black hole Sagittarius A* at the center of our galaxy is 25,900 \(\pm\) 1,400 light-years.)

Messier 3 in Canes Venatici. Click for larger picture.
M3 also beats out M13 in the number-of-stars department, having perhaps 500,000 compared to M13's 300,000 which puts it at about half the number of Omega Centauri, and in the top few percent for Milky Way globulars overall. This unusually large population is probably one reason so many variable stars have been discovered in it.

Currently M3 is cruising at about 40,000 light-years away from the galactic core, which is quite respectable when you consider that the Milky Way is only about 100,000 light-years across, and which puts M13 even further from the core than we are from M13. (You know you're an astronomer when you find yourself saying things like “only one-hundred-thousand light-years” – that's only about six-hundred-thousand trillion miles, for you curious.) Despite this distance, it probably has a better view of the core than we do as it is about 33,000 light years above the plane of the disk, while we have to look through all the dust and gas in the plane of the galaxy between us and the core.

Wednesday, April 11, 2012

Red-letter Day.

You never whom you might meet on Mauna Kea. Famous astronomers and dignitaries come from the world over to Mauna Kea, and since there's only one road to the top, they tend to concentrate along it.

Case in point, I had to work on Easter this year, and thanks to our driver we made it up to Hale Pōhaku in really good time. I was the second person to the cafeteria counter and was waiting for my omelet when a man I hadn't seen before came up and struck up a conversation. He then proceeded to introduce himself as Mead Treadwell, Lieutenant Governor of Alaska, and joined me and my co-workers for breakfast. Turns out he's the head of an association of states with investments in aerospace industries, and he had come to Mauna Kea to check up on the PISCES robotics project that NASA runs there every year. (PISCES is an initiative for testing various technologies that could someday go into space. Since Mauna Kea is the closest analog to Mars we have, they test out various rovers and things that might someday be rolling around on the Red Planet.)

Mr. Treadwell was quite friendly and polite, even handing out hot-cross buns from his favorite bakery in Anchorage to everyone. It was quite an enjoyable experience, and would have been enough to make it a special day, but that afternoon we also received a visit from Scott Losmandy and his wife.

Mr. Losmandy is the creator of the eponymous Losmandy mount, a popular mount system for telescopes. In fact, we use it for three of our telescopes. Mr. Losmandy turned out to be a humble and unassuming man, and we wouldn't even have known it was him if his wife hadn't blown his cover. Once we found out, however, he was very nice and even showed us how to fix a slight problem we'd been having with touchy power connectors on the Losmandy mount. They wanted a picture of one of our telescopes on its Losmandy mount, but their camera was out of battery, so I took the following picture and sent it to them.

Our three Solar telescopes on their Losmandy  mount.
(The wheels and triangular base aren't part of the Losmandy mount, it's basically the legs and the control box that rotates the telescope to counteract the rotation of the Earth.)

As you can see, you never know whom you'll bump into when you work on Mauna Kea!

Monday, April 9, 2012

Non Est Hic!

Qui dicit illis: “Nolite expavescere: Jesum quæritis Nazarenum, crucifixum: surrexit, non est hic, ecce locus ubi posuerunt eum. Sed ite, dicite discipulis ejus, et Petro, ‘quia præcedit vos in Galilæam: ibi eum videbitis, sicut dixit vobis.’ ”
 – Mark 16:6-7
He said to them: “Do not be amazed; you are looking for Jesus the Nazarene, who has been crucified. He has risen, he is not here! But go, tell His disciples and Peter, ‘He is going ahead of you to Galilee; there you will see Him just as He told you.’ ”

Joyful Easter everyone!

I now have a strong desire to work the phrase “non est hic!” into a conversation somehow.

Saturday, April 7, 2012

Daniel Berke and the Transit of Venus

I've let a few hints slip in some of my previous posts of a big event happening this summer, something called a “transit of Venus”. Given that as of the 5th we are only two months away from the big event, I'm going to kick off a series of posts about the subject from now till then.

First of all, you're probably wondering, what is a transit of Venus, and why is it such a big event? To start with, a transit in astronomical terms is when one object passes in front of another, and the transit of Venus is when Venus will pass in front of the face of Sun as seen from Earth.

Ok, you may be thinking, but why is it such a big deal? The answers is that transits of Venus are rare. Venus goes around the Sun in 224.65 days compared to Earth's 365.26 days, so Venus actually passes between the Earth and the Sun every 584 days, on average. If Venus actually crossed the Sun's disk every time every time this happened, they'd be about on par with total solar eclipses in rarity.

But they don't. Because of the way the orbits of Venus and Earth are aligned, Venus normally passes above or below the Sun as seen from Earth. It works out that transits of Venus only happen in pairs eight years apart, with either 105.5 or 121.5 years between pairs. The specifics of why this happens are fascinating, and something I'll go over in greater detail in a later post.

Anyway, because of their rarity, only six transits of Venus have ever been observed since the invention of the telescope over four hundred years ago: one in 1639, a pair in 1761 and 1769, a pair in 1874 and 1882, and one in 2004. But it's not just their rarity that makes them interesting. With the right measurements, a transit of Venus can be used to figure out the distance from the Earth to the Sun. Back in the 18th and 19th century, this was big news, because that distance was unknown at the time.

In fact, it was such big news that it sparked one of the first examples of international scientific collaboration on a significant scale. Dozens of expeditions were dispatched by quite a few countries to every corner of the globe in order to get as many different measurements as possible (I'll explain why it was necessary to get widely separated observations in a later post). Indeed, Captain Cook, whose third voyage made him the first European to discover Hawaiʻi, first traveled to the South Pacific (Tahiti to be specific) in charge of one such expedition.

If you've been paying attention to the numbers, you'll realize that since the last transit was in 2004, the next one won't be until 2117, so this is the last one to be seen in our lifetimes. It's also going to be visible in its entirety from Hawaiʻi, so we are expecting major crowds at the Mauna Kea Visitor Information Station where I work. While I'm excited that many people will get to see this historic event – and who knows what future great astronomers may be inspired by seeing it? – I'm also starting to feel a little overwhelmed due to the enormous number of things that need to be put in place for it to happen.

To that end I decided to put together a little humorous poster to help take my mind off all the stuff I need to get done. One of the things I'll be doing for my job in the immediate future is creating designs for a set of limited edition “Transit of Venus” T-shirts we'll be selling on The Big Day. I'm enjoying this assignment because I enjoy making astronomical art, and the stuff I've been coming up with inspired me to create this:

(Click for full size.)

I also have some prototypes of possible shirt designs done at this point in a similar vein, but I'm going to hold off on posting them till we figure out what we want to use for the official shirt. I do have some concept art for the title you can see though.

Anyway, look forward to future posts where I go over more of the fascinating science and history associated with transits of Venus. A hui hou!

Thursday, April 5, 2012

Southern Winter Milky Way Skies.

Today I want to do something a little different and share a picture taken by my housemate and good friend Jonathan. He's recently gotten into astrophotography using his DSLR camera, but has been too busy to do much (it being his last semester at UHHilo and all).

Two weeks ago he was able to make it up to the Vis and took the following picture, which he posted on his blog (which you can find at Life is a Zwitterion). I saw it and offered to label the constellations and a few other objects visible in it for him, and he suggested I post it on my blog, so here it it. Thanks Jon!

This is a 30-second exposure taken from the Visitor Information Station on Mauna Kea looking south at 8:25 on March 19th, 2012. Visible near the bottom is the flank of Mauna Loa, with part of the rim of Puʻu Kalepeamoa visible in the foreground (ka lepe a moa means "the comb of the rooster" in Hawaiian, which is  an apt description for the shape of the range of hills it is part of). In the background lies a stretch of the winter Milky Way, with several prominent constellations visible.

Also visible in this picture are the two brightest stars in the night sky, Sirius and Canopus. Sirius is one of the twenty closest stars us, a mere 8.6 light-years away. It is actually a binary system composed of a white main sequence star (Sirius A) of spectral type A1 about twice as massive as the Sun and about 25 times as luminous, and a white dwarf (Sirius B) first discovered in 1862. Sirius B has a diameter of about 12,000 kilometers (7,500 miles), nearly the same as Earth, but contains 98% of the mass of the Sun.

The other bright star, Canopus, is much further away: 310\(\pm\)10 light-years. Canopus is a supergiant star of spectral type F, and it is 13,600 times more luminous than the Sun. In fact, it's the most intrinsically luminous star within ~700 light-years. Unfortunately, it's far enough south as not to be visible from much of the continental United States, although south of 37\(^\circ\)18' it may be visible under very good conditions.  Its radius is fully one-third of the distance from the Earth to the Sun, about 50 million kilometers or 30 million miles.

Along with stars, there are quite a few constellations (or parts of them) visible in this image. Prominently placed is Canis Major, the Big Dog (Canis Minor is out of the top of the picture, however). The three constellations that made up the old constellation Argo Navis are also visible here; Puppis, the Poop Deck, Carina, the Keel, and Vela, the Sail. Also visible is Pyxis, the Ship's Compass, though it is a modern addition by Nicolas Louis de Lacaille in the 18th century. Below Canis Major is Columba, the Dove, and Pictor, short for Equuleus Pictoris the Painter's Easel (another modern addition courtesy of de Lacaille). Finally, just at the bottom of the picture is Dorado, the Swordfish. Dorado is interesting because it contains both the majority of the Large Magellanic Cloud (one of the Milky Way's satellite galaxies) and the south celestial pole. In fact, if it weren't for Mauna Loa getting in the way, the Large Magellanic Cloud would be visible at the bottom of the picture.

Finally, there are at least three Messier objects visible in this picture (there are probably even more that I missed): M46, M47, and M41. Messier 46 you may recall as the open cluster with superimposed planetary nebula I showed a picture of a few weeks ago.

Monday, April 2, 2012

Supernova Hat Trick.

The last year has really been pretty good for astronomers studying supernovae. I glossed over it in my post about them, but there is still much we don't know about supernovae. This is mainly because they're so rare. Basically, the more massive the star, the fewer of them there are. Stars large enough to go supernova make up only a tiny fraction of the stars in a galaxy, much less than 1%. (For comparison, our own Sun, often called a fairly average star, is still larger than 80% of the stars in the universe, and star don't really go supernova until they're nearly ten times more massive than that.) Typically in a spiral galaxy like the Milky Way one supernova will go off on average every fifty to a hundred years. However, there a lot of galaxies out there, so if you watch enough galaxies frequently enough you should catch one going off eventually. This is the basis behind all systematic supernova hunts, which can image tens of thousands of galaxies night after night.

This sounds like good news for supernova hunters, but the hidden catch is that many (most) of these supernovae are very, very far away, simply because the majority of galaxies in the universe are very, very far away. This makes them hard to study and analyze because they're hard to see well so far away. It's not often that we get supernova within a few dozen million light-years or so, but in the space of the last ten months we've had three of them go off within 40 million light-years, all three in bright galaxies on the Messier list. And no, despite the date of this post, I'm not making this up.

In June we had SN2011dh go off in M51, 23\(\pm\)4 million light-years away, then in September SN2011fe went off in M101 at 20.9\(\pm\)1.8 million light-years. Finally, on March 16, supernova SN2012aw was discovered in M95, about 32.6\(\pm\)1.4 million light-years away.

I wasn't able to get a picture of it before due to bad weather, but last Thursday the stars finally aligned for me (or, rather, the clouds finally got out of the way) and I was able get the picture you see below:

Messier 95 (bottom, with SN2012aw) and Messier 96 (top) in Leo. North is to the left.

At the top of the picture you can see Messier 96, a galaxy close to M95. At the bottom you can see M95, with SN2012aw marked. Remember, every other star you see in this picture is part of the Milky Way, and SN2012aw is outshining many of them, despite being over three thousand times farther away. That's how powerful a supernova is (not to mention that it's still putting out an amount of light comparable to the rest of M95, two weeks after it went off).

Also, I just wanted to mention that I think the central detail on M95 is really pretty. That's a pretty nice ring of star formation there around the central bar.

Sunday, April 1, 2012

Two Clusters for the Price of One.

I was digging through my astrophotography folder recently and discovered a picture of the Double Cluster in Persues I'd taken last November that I hadn't reduced yet. I speedily corrected that, and now have a picture of the Double Cluster for your perusal.

The Double Cluster is a pair of open clusters cataloged as NGC 884 and NGC 869, respectively. (They also have the older names of χ Persei [that's the Greek letter chi] and h Persei.) Located in the constellation Perseus, they appear very close to each other on the sky. These two clusters are pretty easisly visible as a faint misty patch close to the border with Andromeda. They are located at distances of 7,600 and 6,800 light-years from Earth, so they are also not too far apart in space.

Anyway, enough exposition, have a picture!

NGC 884 (left) and NGC 869 (right), the Double Cluster in Perseus.

Being open clusters, there really isn't that much more I can think to say about them (since they don't have any stand-out features like a planetary nebula in from of them). They were apparently known from at least as early as 130 B.C. (though what they were wasn't know, of course). William Herschel, of Uranus-discovering fame, was apparently the first person to realize that they were two distinct clusters instead of one. Interestingly, they don't have a Messier number, so Messier either never came upon them, or, more likely, found them sufficiently obviously un-comet-like that he felt no need to include them in his list. Considering they can be made out with the naked eye, I'm guessing the latter is more likely.