ALIENS!

This articles came out this morning from MIT, detailing the work of a team of scientists in the UK on the remains of a meteorite, which landed in Sri Lanka this December. I don't want to give away any punch lines or anything (I'm going to), and you should read it yourself, but they're claiming to have found non-terrestrial microbial fossils on the meteorite!

Mercury's Perihelion Advance

I seem to read a lot about (or, at least, I used to, when I had time) Mercury's anomalous orbit. It feels like every physics book I picked up (not counting text books) that talked about astronomy, cosmology, or gravity, mentioned the anomalous orbit of Mercury. I never actually looked up what that meant until just now (none of said books explained what "perihelion advance" meant. Probably should have looked it up five years ago). Anyhow, here's about Mercury's orbit, kinda neat stuff!

First off, what is anomalous about Mercury's orbit? It looks something like this, over time (obvious exaggerated but you get the point):

So what? Don't all the planets do that? Yeah, but Mercury's advance is 43.1" per 100 years greater than the calculated value. So, in other words, Mercury's perihelion is 43.1 arcseconds away from its expected position every 100 years. This anomaly was first measured in 1859 by Urbain Le Verrier. Initially there were numerous possible solutions presented (including the theory that there was another, smaller, planet inside Mercury's orbit). At one point or another, it was even claimed that such a planet had been observed (they named it Vulcan). It is now clear that there are no other planets inside Mercury's orbit (I think we would have found them, by now); so what's causing the shift?

First, a little more about the orbit: we can measure the precession of Mercury to be 574.10±0.65 arcseconds/century. So what contributes to that? 531.63 ±0.69" can be attributed to the gravitational pulls from the other planets. 0.0254" are due to the not-quite-spherical shape of the sun (it's measurably oblate). This leaves 42.98 ±0.04" unaccounted for.

The solution was finally reached by Einstein's theory of General Relativity. It turns out that the equations behind Newton's gravitational theory (which predict no precession for the orbit in the absence of other celestial bodies) are slightly off from those designed in Einstein's gravitational theory. The differences are more noticeable in Mercury's orbit because of how close Mercury is to the sun. The other planets also have measurable perihelion advances, but they're substantially smaller than Mercury's.

When you run through the equations for Newtonian gravitation, you get the orbit of an ellipse. If, on the other hand, you work out the orbit using General Relativity you get something really ugly that I don't want to type up. If you're interested in the math you can find it all here, which, incidentally, is a good read on the subject, even if you're not interested in the math. So there you have it! Mercury's orbit is anomalous because Newtonian Gravitation is not quite correct.

Newton. Because kitties named after physicists.

References:
Perihelion Advance image by - European Space Observatory
Tests of General Relativity - Wikipedia

Path of the Moon

I thought this was kind of neat. Not because it's particularly exciting or insightful, just because it's something that pertains to our (semi-) every-day lives (as close as one gets when talking about astronomy, I suppose), and we (or at least I) never really think about it. Off the top of my head I wouldn't really think of the moon's orbit in this shape.

Obviously this is not to scale. But the point is that if I had drawn the moon's orbit without really thinking about it, it would have come out something like:

Which is not actually the case. The orbit of the moon is actually a thirteen-sided... uh... polygon? I don't know what you'd call it. Anyway, it looks more like a circle, to scale. You might expect it to be 12 sided, for each of the months, but due to the fact that our calendar does not perfectly match the phase of the moon, it's more like 13. Anyhow, if you tweak the parameters so that you can actually see the shape, rather than a circle, you get this:

Which seems totally counter-intuitive!

References:

Helmer Aslaksen - National University of Singapore

James Webb Space Telescope

I think we were supposed to write about a telescope. It may have been a couple weeks ago that we were supposed to do this, but hey, better late than never, right? I chose a telescope that doesn't exist yet, because what we don't have is always more exciting than what we do have.

So here's the telescope:

Or at least, what the telescope will look like. And also what the people working on it look like. It's called the James Webb Space Telescope (JWST), and should be the next big thing in space telescopes, after the Hubble Space Telescope is past its prime.

The JWST will be an infrared telescope with a 6.5 meter mirror, and will detect wavelengths between .6 and 28 micrometers.  Astronomers have high hopes that it will allow them to look even farther back (read: farther away) in the universe than we've ever seen before. It's also kind of neat in that it's actually an international collaboration (I suppose this makes sense, since we don't really have any boarders in space) between the US, Canada, and Europe (That would be NASA, CSA, and ESA, respectively).

There's a whole bunch of new technology going into this telescope, which you can read about here. I don't really want to get into all of it, but in short the design of the telescope and a lot of the pieces in it are completely new technologies. Hopefully they all work like they're supposed to!

The JWST is scheduled to launch in 2018 from French Guiana (which is on the northern-ish coast of South America). It will be orbiting about 1 million miles outside the orbit of the earth, so that it can block out any heat-noise from the earth, the sun, and the moon all at the same time.

References:
Image by NASA James Web Space Telescope - People
James Webb Space Telescope

The Drake Equation

As far as completely useless equations go, my favorite is probably the Drake Equation. This may or may not be because it's the only completely useless equation that I know. It's kind of neat, anyway. Basically, the Drake Equation (thought up by Frank Drake--he's got two first names--in 1961) is to calculate the number of detectable aliens in the universe. It goes something like:

Where 

N = number of alien civilizations

R* = avg. rate of star formation

f_P = fraction of stars with planets

n_e = avg number of life-supporting planets per star

f_l = fraction of potentially life-supporting planets that actually develop life

f_i = fraction of f_l  that actually develop into intelligent life forms.

f_c = fraction of f_i that develop technology that make it easier for us to find them

L = length of time that civilizations have had above technology

So why is it useless? Because almost all of the above are unknowns. We can get a pretty decent number for average star formation, and even for fraction of stars with planets, but the rest? So far, the only criterion for life we have is water. How many planets have water? No one actually knows. It just gets more questionable from there.

Essentially, you can turn N into whatever number you want, depending on how optimistic you're feeling that day. It's a kind of neat idea, sure. But does it actually give us any sort of useful information at all? Nope. None, whatsoever. But who cares. Because aliens. And Frank Drake is just a pretty cool name.

References:

Drake Equation: Wikipedia.org

Image from The Meta Picture

Pluto Rant

People seem to whine a lot about Pluto not being a "planet" anymore, since it was entitled a "dwarf planet". Truth be told, I was a little bit miffed myself, but I'm pretty sure I was six at the time.... Maybe twelve. I don't really remember. I do remember wondering what they were going to do with the planet mnemonic, because it used to be "My Very Energetic Mother Just Served Us Nine Pizzas" and now it's... "My Very Energetic Mother Just Served Us Nine." Nine whats? I don't know. I'm not in fifth grade anymore. People don't give you mnemonics for the order of the planets when you're in college.

The point is, it has since been explained to me why Pluto is no longer considered a planet, and it makes a great deal of sense. After all, would you rather memorize eight planets? Or would you rather include Pluto in the definition of a "planet," and then memorize thirteen hundred planets? I'd prefer the eight, thanks.

For the record, I believe the definition of a planet is that it must be large enough to be (roughly) spherical, that is in direct orbit around the sun (so that the moon--which is, coincidentally, larger than Pluto--doesn't count) and large enough to have cleared its own orbit. There are only eight objects in our solar system that fit this definition. If you count Pluto (which is large enough to be roughly spherical, but not large enough to have cleared its orbit of other orbiting bodies), then you also have to include a slew of other orbiting objects... of which Pluto is not, in fact, the largest.

Also, another thing people like to neglect when they're getting butt-hurt over Pluto, is that Pluto is a rock. Pluto does not have feelings. Pluto has no sentience, and is not upset that it is not considered a planet. Why do we get so sentimental about inanimate objects, sometimes?

What are you even doing out there, Pluto?

Semi-Relevant: WTF are Those Red Giants Doing up There?

When one looks at an HR diagram (ie, a Color-Magnitude diagram), one may wonder what those stars are doing, hanging out up above the general trend. Well, I did, anyway. Not right away, mind you, it took at least three years for me to wonder this, between the first time I saw this diagram and the first time I wondered what they were doing all the way up there. It turns out it's not really just the red giants that are doing weird things, and that there are a couple separate groups of stars that don't fall onto the main sequence.

In general, the full diagram would look something like this:

So, the answer to my above question is, as I understand it, that the main sequence actually represents the lifetime of a star. Depending on the star, it may break off and drift up into the realm of the red giants later on in it's life (I think around 10 billion years, ish?). If it's really massive it might not go down the main sequence at all, instead heading straight over to the supergiants. After that, more complicated things happen (ie, it could supernova, if it is a large enough star, and subsequently form a white dwarf...). So, as far as I can gather, the reason there are subsets in addition to the main sequence is that stars change as they age, and different stars age differently.

References:

NASA: Chandra X-Ray Observatory