Stargazing this Week
Planets, Strung Out
We’ve written about planets in these newsletters a lot, and for good reason! They’re not always so easy to spot. This winter we were lucky to see many of the planets at the same time, in the same part of the sky. Times have changed.
Since their near alignment, the planets have strung themselves out across the sky, but much of that line up is obfuscated by the earth -or by daylight. That said, the gas giants Jupiter and Saturn will join the waning moon and get up early to greet you this week.
To find them, look just south of east before dawn breaks. The planets get up marginally earlier each morning, but the moon comes later each day. You can see them together through at least Wednesday, the 7th.
Galactic Coma
Every week I write a newsletter for the Pasayten institute, which is where I get the idea for a lot of these stories! The newsletter typically opens with stargazing. What planets are out, and what constellations or stars are worth checking out.
This week’s subject was obvious. Everyone is talking about it. The Coma Star Cluster - a massive collection of stars near Leo the Lion - is high in the sky.
Bruce McClure has a write up in EarthSky this week about hunting the Coma Cluster, and its worthy challenge. For folks in the Northern Hemisphere, the cluster is high in the southern sky these nights. To find the Coma Cluster, first find the constellation Leo. If you can find the Big Dipper, follow the lead stars away from Polaris - to find the Lion. Leo’s head is represented by a Sickle-shaped asterism, whose handle is the heart of Leo - the bright star Regulus. Just on the other end of the Lion, past it’s tail if you like, you’ll find the Coma Cluster.
I didn’t make this clear in the newsletter, but the Coma Star Cluster is a bunch of stars in our own galaxy. But in the same direction lies something even more interesting. Deeper in space, tucked behind the star cluster (from our perspective at least) is a cluster of galaxies.
The Coma Cluster has a rich history in modern astrophysics; it was one of the first case studies in Dark Matter. As Fritz Zwicky pointed out way back in 1933, the motion of the galaxies in the coma cluster are totally inconsistent with their expected mass - even accounting for observational uncertainties - given how much brightness we can see. The best theoretical explaination so far? There must be a whole bunch of matter that doesn’t glow or reflect light: the Dark Matter. And there must be a lot of it
How could we know that? Well. We know a LOT about stars. Mostly because there are so many of them. Extrapolating our knowledge of stars and our knowledge of the laws of gravity, we can estimate the amount of mass in a given gravity by it’s brightness, shape and distance: all three measurements we can definitely make.
Plugging all the those data into our models of gravitation, the results are clear: The galaxies in the coma cluster are moving as though they were under the influence of some serious extra mass.
Other observations - like the famous bullet cluster - have led astrophysicists to the conclusion that dark matter is likely a kind of particle. But it has to be a particle that doesn’t interact with electromagnetic waves - that is, with light. It has to be dark. The only particle that we’ve observed that fits that bill is the neutrino. But calculations have shown that it can’t be neutrinos. So it has to be something else, right?
We’re still looking for what dark matter might be.
