Sunday, July 31, 2011

Centaurus A, Wild and Wonderful Galaxy


Today I've got a picture of an amazing galaxy for you to enjoy, Centarus A. I took this picture a little over a year ago. Centaurus A is a really strange beast in a universe full of exotic galaxies. You know, you'd think I wouldn't be continually surprised at the fact that the pictures I take look like the ones I see that other people have taken, but for some reason I'm always pleasantly surprised that my pictures look just the way I expect an object to look.

Centaurus A, unusual galaxy. In Centaurus, obviously.
If it weren't for that highly unusual dust lane running across it, Centaurus A would appear to be a fairly normal elliptical (or possibly lenticular) galaxy. But that dust lane immediately transforms it into a galaxy of much interest to astronomers. That dust is there because Centaurus A is actually two galaxies undergoing a collision; an elliptical galaxy, and a spiral galaxy like our Milky Way. The dust acts as a highly efficient blocker of light, causing the dark stripe you see in the image.

Centaurus A lights up the sky in radio wavelengths due to two humongous radio-producing lobes coming from both ends (the upper left and lower right in this orientation). These lobes come from bits of gas accelerated to about half the speed of light by a supermassive black hole that resides in the center of the composite galaxy and extend for hundreds of thousands of light years in space. If we could see these lobes with our eyes, each of them would appear several times larger than the full Moon on the sky (Centarus A itself is about 2/3 the size of the full Moon).

Centaurus A is a relatively nearby galaxy, somewhere between 10-16 million light years away (that's about 60-86 quadrillion miles, or 60-86,000,000,000,000,000,000 miles). It's also one of the brighter galaxies on the sky, which is one reason I was able to get such a good shot of it. All in all it's a fascinating galaxy, and one that I'm highly pleased I was able to get a picture of.

Monday, July 25, 2011

Globular Cluster Photo Series (Part 8): M72

Today I have a picture of Messier 72 for your perusal. This is one of the farther clusters from us, at a whopping 55,000 or so light years (keep in mind that the Milky Way galaxy is about 100,000 light years or so in diameter, or roughly six hundred quadrillion miles). It is located in the direction of the constellation Aquarius, which combined with its great distance places it on the far side of the galactic core from us. It's the smallest cluster in apparent angular size we've looked at so far at a miniscule 6.6 arcminutes in diameter, about a fifth as wide as the full Moon.

Messier 72 in Aquarius.
While it appears faint to us, the great distance of M72 means that it is actually one of the more intrinsically luminous globular clusters out there. At 106 light years in diameter it's fairly average sized, but has an unusually large number of variable stars, at least 44. It's also one of the least concentrated clusters, by which I mean that it has a very even distribution of light instead of a much brighter spike in the middle (look back at earlier pictures to see examples of more concentrated clusters). And other than that, there's not much for me to say about it except that I still think it's kind of pretty.

Saturday, July 23, 2011

Ring Around the (Crater) Lake

First of all, I haven't received my new power cable yet, but my brothers dug up one rated for 90 watts that fits the socket on my laptop, which is enough to run my computer on fairly simple tasks. I need 120 watts for full power, so I still need the new cable, especially as I like to perform fairly power-intensive tasks with my computer.

Recently my family took a trip up to Washington for a family reunion, and I got a lot of photos along the way. On the way up through Oregon we stopped at Crater Lake, where I was able to take enough photos (6 in this case) to assemble a panorama.

Crater Lake, Oregon. Wizard Island is visible on the left. Click on it for a larger version!
Crater Lake is really an amazing place. It's located in the caldera of an ancient volcano known as Mount Mazama that was probably around 12,000 feet high before it blew its top in a spectacular eruption a few thousand years ago that dropped its height by nearly a mile (the highest point on the rim now is 8,159 feet). The average lake surface level is at 6,178 feet above sea level, while the maximum depth of the lake has been measured at 1,949 feet, making it one of the deepest lakes in the world.

The eruption of Mount Mazama was a truly monumental event (the name comes from a Native American word that means “mountain goat”, although the name was given by a hiking club from Portland in 1896). According to estimates it released around 25 cubic miles of tephra (which is a geologist's word for “pretty much anything a volcano erupts that isn't lava”, basically ash, cinders, and rocks). For comparison, Mt. St. Helens released a mere 0.67 cubic miles of tephra during its eruption of 1980, and when Krakatau blew up in 1883 it released about 5 cubic miles of stuff. Twenty-five cubic miles is a lot of ash. According to the visitors' center it would be enough to blanket Oregon to a depth of 8 inches.

One cool thing about Mount Mazama's eruption is the fact that it occurred within living memory of the local Klamath tribes, who passed on oral history accounts of the eruption. That must have been a sight to see (and survive) indeed!

Monday, July 18, 2011

Computer Troubles (Again)

This evening I discovered that the power adapter for my laptop was making a strange clicking noise. More importantly, it doesn't work. Since I'm going to have to get another one and won't be able to use my computer until I do, I probably won't be updating my blog very frequently for a while.

Tuesday, July 12, 2011

Globular Cluster Photo Series (Part 7): M69

Today's globular cluster is Messier 69 in Sagittarius. It's a fairly small cluster only 84 light years in diameter and a mere 9.8 arcminutes in apparent size. This is because it is fairly far away from us, about 29,700 light years away.

Messier 69 in Sagittarius.
Charles Messier discovered M69 on the same night he discovered M70, on August 31, 1780 while looking for an object described by Nicolas Lacaille in 1751-2. The two globular clusters are fairly close to each other, only about 1,800 light years apart. I'll have to put M70 on my list of objects to observe when I can, so I can properly document this pair. Both of them are fairly close to the galactic core, only about 6,200 light years distant. Like many of the globular clusters I'll be showing from now on, there isn't that much else to write about it, except that it is one of the most metal-rich globular clusters known (i.e., its stars contain a higher percentage of elements more massive than helium than most other globular clusters, though still much less than the fraction of such elements in the Sun).

Monday, July 11, 2011

Globular Cluster Photo Series (Part 6): M28

Today I have an image of the globular cluster Messier 28 for your perusal. M28 is located in Sagittarius not too far on the sky from M22 between 18,000 and 19,000 light years away, with 18,300 being the closest figure I could find. It's the smallest globular cluster I've shown yet, only about 60 light years in diameter.

Messier 28 in Sagittarius.

Its apparent diameter is a miniscule 11.2 arcminutes, making this also the smallest globular cluster by size on the sky that I've shown - the full moon would appear about three times as wide as this cluster. M28 has the distinction of being the second globular cluster where a millisecond pulsar was found (the first was M4, the first in my photo series). It is now known to contain 8 such pulsars. Other than that, I don't have too much to say about it.

Sunday, July 10, 2011

Happy Anniversary, Neptune!

According to the calculations presented in this blog post, Neptune will complete its first orbit around the Sun since it was discovered in 1846 on Monday July 11 at about 1:50 PM in the afternoon Pacific Daylight Time (21:48 UTC, plus or minus 15 minutes). There are actually several dates floating around, the most common being July 12. However, that date is calculated based on Neptune's position around the Sun, while the July 11 date is calculated based on Neptune's position relative to the Solar System's center of mass, or barycenter. Normally the barycenter can be approximated as being within the Sun, but when you're calculating orbits that range over dozens of decades you need to take into account the fact that it actually is periodically outside the Sun, which was surprising  for me. The blog post I linked to has a nifty picture that shows how the barycenter moved relative to the Sun over the last half-century or so. The post itself is a bit long, but not too technical, and the author does an excellent job of explaining his decisions and calculations which is why I'm going with his date for the event. In any case, even if it turns out to be incorrect, what's a day or two off in a orbit lasting 164.79 Earth-years?

Sunday, July 3, 2011

Alpha Centauri

Disclaimer (7/7/11): In at least two of my recent posts over the past few days, I made a major goof concerning the nearest stars to the Sun. I labeled them as Alpha and Beta Centauri, when in reality, the stars are known as Alpha Centauri A and B. (Proxima Centauri was labeled correctly). Beta Centauri is another star system altogether, a triple star system about 350 light years away consisting of two blue-white giant stars about 10-11 times the mass of the Sun and 15,000 times as bright, plus a third star that takes about 250 years to orbit the other two. So, extremely different from the Alpha Centauri system. I've gone back and edited the offending posts, so they should be correct. And if you ever notice an error in one of my posts, just drop me a comment and let me know! I'm happy to admit my blunders if they lead to greater enlightenment for others.

A few days after posting my image of the distance between the Sun and its nearest neighbors compared to the average distance between stars in Omega Centauri, The Astronomy Picture of the Day site had a nifty image of the entire triple system, showing the brightness variation between Alpha Centauri A and B and Proxima, which is something I could not do effectively in my picture. You can check out the picture at the APOD website here.

Actually, I suppose I could have hinted at the difference if I'd made Proxima a single faint red pixel compared to A and B.