We call our galaxy
The Andromeda Galaxy (M31) is indeed approaching us, by about 300 kilometers (190 miles) per second measured with respect to the Sun. If you subtract the Sun's orbital motion around our galaxy (about 230 km per second toward Cygnus), M31 is still approaching the Milky Way by about 130 km per second.
Our home galaxy, the Milky Way, contains at least 100 billion stars, and the observable universe contains at least 100 billion galaxies. If galaxies were all the same size, that would give us 10 thousand billion billion (or 10 sextillion) stars in the observable universe.
We live on a planet called Earth that is part of our solar system. But where is our solar system? It's a small part of the Milky Way Galaxy. A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems.
Andromeda, also known as Messier 31 (M31), is a spiral galaxy located about 2.5 million light years away.
But the Andromeda galaxy is a whole separate galaxy, even bigger than our Milky Way. In a dark sky, you can see that it's big on the sky as well, a smudge of distant light larger than a full moon. View at EarthSky Community Photos.
In 2005, an eclipsing binary star was discovered in the Andromeda Galaxy. The binary is two hot blue stars of types O and B. By studying the eclipses of the stars, astronomers were able to measure their sizes.
The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across.
We live in one of the arms of a large spiral galaxy called the Milky Way. The Sun and its planets (including Earth) lie in this quiet part of the galaxy, about half way out from the centre. 100 000 years to cross from one side to the other.
It takes 250 million years for our Sun and the solar system to go all the way around the center of the Milky Way. We can only take pictures of the Milky Way from inside the galaxy, which means we don't have an image of the Milky Way as a whole.
As it stands, the universe is the largest object that we are aware of. There is nothing larger, and everything we can smell, hear, taste, touch, or see is a part of it.
Even though certain features of the universe seem to require the existence of a multiverse, nothing has been directly observed that suggests it actually exists. So far, the evidence supporting the idea of a multiverse is purely theoretical, and in some cases, philosophical.
The world as we know it has three dimensions of space—length, width and depth—and one dimension of time. But there's the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions.
Our Milky Way galaxy is destined to collide with our closest large neighbour, the Andromeda galaxy, in about five billion years. Scientists can predict what's going to happen. The merger will totally alter the night sky over Earth but will likely leave the solar system unharmed, according to NASA.
It is estimated that there are roughly 200 billion galaxies (2×1011) in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs).
Can the Andromeda Galaxy support life? Since we can't yet say for certain whether there are any other stars in our own galaxy that host life, it is even harder to say whether there might be life, or at least the conditions for life, in another galaxy.
So, to leave our Galaxy, we would have to travel about 500 light-years vertically, or about 25,000 light-years away from the galactic centre. We'd need to go much further to escape the 'halo' of diffuse gas, old stars and globular clusters that surrounds the Milky Way's stellar disk.
One such estimate says that there are between 100 and 200 billion galaxies in the observable universe. Other astronomers have tried to estimate the number of 'missed' galaxies in previous studies and come up with a total number of 2 trillion galaxies in the universe.
Because space isn't curved they will never meet or drift away from each other. A flat universe could be infinite: imagine a 2D piece of paper that stretches out forever. But it could also be finite: imagine taking a piece of paper, making a cylinder and joining the ends to make a torus (doughnut) shape.
Thanks to dark energy and the accelerated expansion of the Universe, it's physically impossible to even reach all the way to the edge of today's observable Universe; we can only get a third of the way there at maximum.
Black holes have two parts. There is the event horizon, which you can think of as the surface, though it's simply the point where the gravity gets too strong for anything to escape. And then, at the center, is the singularity. That's the word we use to describe a point that is infinitely small and infinitely dense.
As a universe, a vast collection of animate and inanimate objects, time is infinite. Even if there was a beginning, and there might be a big bang end, it won't really be an end. The energy left behind will become something else; the end will be a beginning.
Now the Andromeda galaxy can be seen with the naked eye, like a tiny dot in the sky. But in three billion years it will be so clearly visible to the naked eye that it will even be possible to see individual spiral arms in it.
Someday our little corner of the universe will have a ringside seat for one of the biggest events in the cosmos. Two billion years from now, the Milky Way and Andromeda, our closest neighboring galaxy, will begin to fuse into one giant football-shaped galaxy.
Will humans survive the Andromeda collision? A: There is a 1 in 400,000 chance that humans will survive the Andromeda collision.