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.

The Great Nebula in Orion.

Last Wednesday I was able to take out the imager at the Vis under good conditions for all of the second time this year.

Since it's still winter in the northern hemisphere, and the Earth's night side is still pointed more or less away from the galactic core, there aren't many of the objects I typically like to image (globular clusters) out at night. This led me to look around for another object to image, and I settled on the Great Nebula in Orion, AKA Messier 42, AKA the Orion Nebula. This nebula is, without a doubt, the most impressive nebula in the sky. It's also the brightest, and one of the few that can be seen with the naked eye (it's the middle "star" in the three stars that make up Orion's sword. No, not his belt, but his sword. I should post a picture...). I decided to devote an entire night to it and ended up getting almost two hours' worth of exposures. (Normally I like to image as many things as possible in a night, and for things like globular clusters that works alright, but the picture I got has taught me to reconsider that position when imaging nebulae...)

But enough words! You want to see the picture, and I want to show it to you:

The Great Nebula in Orion, Messier 42.

Gorgeous, no?

The Orion nebula is the closest star-forming region (or "stellar nursery") to Earth, at 1,344 \(\pm\) 20 light-years distant. It is probably the most photographed celestial object in history \(-\) in fact, it was the very first nebula ever to be imaged, on September 30, 1880 by Henry Draper (who was a pretty amazing character, one of the pioneers of astrophotography, and the person in charge of the U.S. expedition to observe the transit of Venus in 1874).

The Orion nebula is a large ball or bubble of gas (which fluoresces red) and dust (which silhouettes as black, or reflects light as blue) about 24 light-years across. Several extremely young and massive stars much hotter and more luminous than our Sun have formed near the center and are steadily blowing a hole in the side of the bubble of gas and dust in which they are embedded. The four brightest are known as the Trapezium and are a little too bright to see in this picture (they're located in the center where it's brightest). This allows us to see into the central cavity.

Interestingly, it's quite possible that the Orion nebula doesn't look anywhere near as impressive from the other side. From that perspective it might appear as a mostly featureless dark nebula, with perhaps some small emission nebulae around the edges. This is because the stars in the Trapezium appear to be blowing open the side of the bubble asymmetrically, and we happen to be on the side where it's open. It does make you wonder about the other dark nebulae we can see in the sky, and whether they might not be visions of such cosmic grandeur from the other side...

One last note: on the left side of the image, you might be able to make out two faint straight lines. Those are satellite tracks that appeared in the luminance images while I was imaging. They're pretty faint, so you may or may not be able to see them.

Globular Cluster Photo Series (Part 15): M79

Today I have another Messier globular cluster to show you, Messier 79. This one is located just below Orion's feet in the constellation Lepus, the Hare. M79 is fairly small on the sky, just 8.7 arcminutes across (less than a third the width of the full Moon). This is mainly due to its large distance of about 42,000 light years from us, as the cluster itself is roughly average in size at about 118 light-years across.

Messier 79 in Lepus.

There are two very interesting things about Messier 79, and they may be related to each other. First, M79 is in an unusual position for a globular cluster: it's almost directly opposite from the galactic core in the sky. By far the majority of globular clusters are located somewhere in the same hemisphere as the core (and hence are visible during the summer); M79 is one of the very few that's not.

Secondly, M79 may not be native to the Milky Way. It is possible that it (along with three other smaller, fainter globular clusters) were originally satellites of another dwarf galaxy that is in the process of being absorbed into the Milky Way. A candidate galaxy was discovered back in 2003 and is known as the Canis Major Dwarf Galaxy based on the constellation in which it was first discovered in. I say "candidate" because it is still not entirely certain if this galaxy actually exists as an independent galaxy or is simply an over-dense part of the Milky Way. This is because it lies behind the galactic disk from our vantage point, making it impossible to see in visible light and difficult to analyze.

If the Canis Major Dwarf Galaxy does exist it would be the closest external galaxy to us, being only about 25,000 light-years away, and actually closer to us than to the Milky Way's core. It seems to correspond with a structure known as the Monoceros ring, an incredibly long stream of tidally disrupted stars that stretches over 200,000 light-years long and wraps around the Milky Way three times. If M79 was originally a satellite of the CMDG it would help to explain its strange position (although it's not impossible for a true Milky Way globular to have such a position; it's just rather unlikely).

Anyway, enough about this unusual globualr cluster; tune in tomorrow to see our very first non-Messier one!

Project Orion

Today I came across what is certainly one of the most intriguing and arguably one of the best ideas the human mind has ever come up with: Project Orion.

Project Orion was a serious research program in the late 40's and 50's dedicated to achieving rocket propulsion in a...slightly unorthodox manner. In essence, it boiled down to chucking atomic bombs out the back of the rocket and detonating them to provide thrust. Mull on that for a few seconds. This was a dead-serious project by some top physicists. The explosion from the bomb would push on a large pusher plate at the back of the vehicle that would be attached with some heavy-duty inertial dampeners causing the whole thing to act like a spring, bouncing back after each explosion only to be greeted with a fresh one for the maximum impulse. Serious calculations showed that it would take about the same about of bombs to get a wide range of payload masses, from 2,000 tons (on the order of the size of the Saturn V rockets that went to the moon) all the way up to 8,000,000 tons (on the order of the size of a small city[!]) into orbit, meaning you could launch much greater masses with the same amount of "fuel" than you could using conventional measures. How many bombs does it take to launch a spaceship into orbit, you ask? The guys in charge of the project have you covered. It would take about 800 nukes at the rate of about one per second to launch something into orbit in a manner akin to "an atomic pogo stick."

Imagine that, if you will.

Imagine being among the first crew to experience one of these. The whole point of the inertial dampener is to decrease the acceleration when the bomb goes off from a lethal 100g to a more human-survivable 2 to 4g, but that's still some significant shock. And every second for over ten minutes you'd get another one. Another interesting fact: the guys in charge of the project were worried that the random nature of the explosive fireballs might send a spacecraft off course, but were reassured when they found that the effects tended to cancel out. Well, that sounds nice in theory, but in reality it means that in addition to the jerky forward motion you'd be feeling, there'd be tiny, random, deviations each time which you know aren't going to knock you off course, but which I'm sure would be pretty unsettling anyway.

Plans for launching such space vehicles included -- I am not kidding here -- covering the landing pad in a layer of conventional explosives and literally blowing the ship far enough up into the sky that it could drop its first nuclear charge without risk of shrapnel from the nuke interacting with the landing pad damaging the ship itself. I mean, how cool is that?? The project ended up being shelved not because of the extreme amounts of fallout it would generate (the idea was never actually flight tested), but because no one at the time could think of a need to launch thousands of tons of payload into space (the signing of the 1963 Partial Test Ban Treaty also made it impossible to test. The U.S. tried to get an exemption for nuclear propulsion into the treaty, but the Russians were [understandably] reluctant).

In the aftermath of bans on open-air nuclear explosions, some people have proposed a similar idea, but one where the spaceship would be launched by more conventional means (or assembled in space) before igniting its nuke drive far enough away from Earth to be non-hazardous. It was calculated that a mission to Pluto and back could be completed in a single year using such a drive. In contrast, New Horizons, the probe currently heading to Pluto, is the fastest man-made object ever, and it's still going to require nearly 15 years to get to Pluto.

And now, perhaps, you can begin to see why I find this idea so fascinating, so captivating, so wonderfully and uniquely "out there" that I could not sleep without writing this post about it. Because when you get right down to it, really, all worries aside, who wouldn't want to ride a nuclear-powered rocket? ("Prime the nuke drive, Scotty!")