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Daily Space: Say hello to the neighbors [1]
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Date: 2022-08-20
The nearest galaxy to our own is Andromeda, which is around 2.5 million light years away. When you’re looking for something that distant in the sky, you might think it will also be some tiny, barely-there dot. Only … Nope.
That’s because the Andromeda galaxy is big. Really big. Its diameter is around 152,000 LY. That’s about 50% larger than our own Milky Way. That combination of width and distance means that the visible part of the Andromeda Galaxy is actually about as big as the full Moon in our skies. Point a telescope in its direction, and the full width of the Andromeda galaxy is actually six times as wide as the full Moon. Told you it was big.
Andromeda. 180 stacked images (30 minutes). Vaonis Vespera.
With good conditions, it’s not difficult to find Andromeda. To the naked eye it’s kind of a grayish smudge. Some old observations have described it as “like a candle flame,” but that only makes me wonder about their candles. The image above is definitely one of those “I should have gone longer” images when it comes to astrophotography, but it’s pretty representative of what you’ll see with a small scope, or even good binoculars, on a clear night.
In any case, the obvious nature of Andromeda means that the “discovery” of this object, which is M31 in old Messier’s catalog, doesn’t go to some 17th or 18th century European who shined up his own telescope mirror. The first star chart to note the Andromeda galaxy was actually produced in 964 by Persian astronomer Abd al-Rahman al-Sufi.
Abd al-Rahman al-Sufi, also known by the Westernized shorthand of Azophi, included the Andromeda galaxy in a marvelous tome known as The Book of Fixed Stars. As the court astronomer to the Shia Buyid dynasty in Iran, al-Sufi was responsible for observing the night sky and noting down what he saw. He also likely did a lot of predicting about things on Earth, as a big concern of his book is some very dynamic and well annotated diagrams of how all the stars fit into constellations, including some familiar zodiac symbols. In many cases, al-Sufi drew the constellations in two versions, one as they are seen from the ground, and another as if he were standing on the opposite side of the stars, looking back at Earth. I have no idea what that was about.
One interesting thing is that al-Sufi based many of his charts on some produced over 800 years earlier by Ptolemy. Because of this, he seems to have left stars off his charts that he noted in observations, but were not found in Ptolemy’s charts. But this didn’t happen to the Andromeda Galaxy, which shows up in both the illustrations and text.
So, get outside, in a place without light pollution, and you can see 2.5 million light years. That seems pretty good.
But you’re still not done. If you can find yourself in a place where the light conditions are really, really good (I suggest middle of nowhere in northwest South Dakota, where I spent the nights during dinosaur digs being absolutely gobsmacked by the sky) you can spot the thing that’s in the image at the top of this article — the Triangulum Galaxy.
It’s only 200,000 light years more distant than Andromeda, and it’s considerably smaller. Only about 60,000 LY in diameter (and yes, this is one of those articles where every use of “only” seems like it should come with ironic quotes). But at 2.7 million light years, it is by most accounts the most distant object visible to the unaided human eye.
You can theoretically see 2.7 MLY before you even pull out a telescope. Look at you!
Oh, and you may be aware that the Andromeda galaxy is making a beeline for the Milky Way, with a collision projected for about 4 billion years in the future. But did you know that Triangulum is also headed our way? Expect it to join the mix around a billion years later.
What can happen when galaxies collide? It doesn’t really mean stars smashing together head on. Or at least, that happens very rarely. But the neighborhood sure can change. See that little blob above and left of Andromeda in the image above? That’s the dwarf galaxy M32. For a long time, it was regarded as a small “early type” galaxy that hadn’t had time or the mass to become more organized. However, later analysis suggests that this is what remains of another galaxy that Andromeda swallowed up about 800 million years ago.
None of this is likely to be a problem for any of us. But hopefully someone, on a planet around some star, will be around for the show.
As many of you are no doubt aware, NASA is getting close to launching the Artemis I mission, which will see the first human-rated ship make an orbit around the Moon since Apollo. This is preliminary to the Artemis II mission that is expected to see astronauts repeat this flight in 2024, and Artemis III that is supposed to finally return people to the Moon’s surface over 50 years after the last Apollo flight.
I had hoped to be covering this event from Kennedy Space Center, but the combination of COVID-19 reducing the available seats in the press center, and not so unexpected high demand, makes it likely I’ll be at digital ringside with most folks. Still, do expect coverage of the flight, as well as some of the press events over the next two weeks.
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