Posted on December 15, 2021
This is an update of my post published on December 15, 2010:
When we say that someone has discovered something, we tend to think that person was the very first to observe that thing. We must always, always remember to add “that we know of,” because we usually go by discoveries and observations that are recorded in some way or passed on to other people. Obviously, a lot of people see things that they don't write down or otherwise record!
In the case of Simon Marius's “discovery” of the Andromeda Galaxy, in 1612, there are a few problems:
- Simon Marius didn't have any knowledge of this, but medieval Persian astronomers had seen this galaxy centuries ago, and it had been described by Al Sufi as early as 964 A.D. (648 years earlier!). We can say that Marius independently RE-discovered Andromeda, and he was the first person to observe it through a telescope. That we know of.
- Simon Marius didn't know that what he was seeing was a separate galaxy. He called it the “nebula in the girdle of Andromeda.” A nebula is a cloud of dust and gas, and until Edwin Hubble discovered that there were other galaxies outside of our Milky Way Galaxy, around 1922, a smudgy patch of light in space was called a nebula.
(Andromeda is a constellation that supposedly pictures a legendary princess wearing a gown and girdle.)
Andromeda, lying down
Who is this Simon Marius fellow?
He was an astronomer from Bavaria, which is now a part of Germany. In addition to re-discovering the Andromeda Galaxy, he named the first four Jovian moons, Io, Europa, Ganymede, and Callisto.
(Jovian means “belonging to, or having to do with, Jupiter.”)
Quick quiz:
As I said above, a nebula is a cloud of dust and gas in space. A galaxy, on the other hand, is a huge group of stars, star systems, dust and gas bound together by gravity, often shaped like a spiral or an ovoid. The nebula we see are by in large INSIDE our own galaxy, and of course the other galaxies are outside our own.
Which of the items below are nebulae, and which are galaxies?
1
2
3
4
 |
| 5 |
By the way...
There are a LOT of galaxies in the universe. Scientists estimate that there might be as many as 200 billion galaxies, each with millions to trillions of stars. Every smudge of light you see in this photo is a galaxy:
ANSWERS:
1. galaxy
2. galaxy
3. nebula
4. nebula
5. galaxy
Did you know...?
- The Andromeda Galaxy is the nearest large galaxy to our own Milky Way Galaxy, and like our galaxy it is shaped in a spiral. Together with one other spiral galaxy and more than 30 other galaxies, many of them dwarf galaxies, these galaxies make up our Local Group.
- As I said, the Andromeda Galaxy is pretty nearby (as galaxies go)—but it's going to get a whole lot closer. We can measure that the galaxy is approaching us at about 120 kilometers per second. Scientists believe that the Andromeda and Milky Way Galaxies may end up colliding! (But don't worry, it won't happen for another 3 to 5 billion years.)
What does a galaxy collision look like?
Beautiful!
What does it sound like?
It's silent, like all collisions in space. There is no air to be compressed into “sound waves.”
What will happen if the expected collision does happen? Will the galaxies explode and be destroyed? Will all the stars smash into each other and annihilate each other?
No. Pretty much everything will be fine. Galaxies are mostly empty space, with the huge distances between stars dwarfing the size of the stars, so it is unlikely that objects inside the galaxies will actually hit one another. If the collision happens, the galaxies will likely merge into one larger galaxy.
The Milky Way galaxy is colliding with (and “eating” or absorbing) a dwarf galaxies even as I type this, and it done so many times in the past as well.
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