What is the Universe?
The universe contains everything that we have discovered; it is the whole cosmos, which is believed to have been formed during the Big Bang, occurring 13.8 billion years ago. We have already discovered 46 billion light-years away from us, therefore this is our current believed universe size, but there may be parts of the universe further away than this that we have not yet discovered due to the fact that the light from them has not yet had enough time to reach us. We also know that the universe is expanding, as all other galaxies except those in the gravitational bound of our Local Group are becoming further away from us, due to the creation of new space between us. However, we don't know if the universe is infinite in size or if it will continue to expand forever. Because of our limited understanding, we do not know if there is more than one universe, or if there is only one, but our current understanding is that there is one universe, and it is the name given to the entirety of everything we know that exists.
There is no images of the universe as it is too massive to explore in its entirety.
What is a galaxy?
A galaxy is a collection of stars, gas, and dark matter bound by gravitational attraction.
The largest known galaxy at this time is known as Alcyoneus, which is 3.5 billion light years away from earth and spans to a size of 42,700 light years. Its central galaxy is thought to hold 240 billion solar masses.
The smallest known galaxy is Segue 2 which is a dwarf galaxy in the constellation of Aries. It holds only around 1,000 stars, and it is 114,000 light years away. Our galaxy (the Milky Way) has star clusters that have more stars than Segue 2 has overall. There are 3 types of galaxy: elliptical, spiral, and irregular. Although some galaxies formed not long after the universe, rendering them only a few hundred million years younger than it, there is evidence that galaxy formation was still occuring less than a billion years ago. When a galaxy is first formed, it is relatively small, but over time galaxies merge to become larger. After 4.5 billion years, our galaxy (the Milky Way) will merge with the Andromeda Galaxy, creating a galaxy with 1.5 trillion stars in it. There is only one universe, which is estimated to have 2 trillion galaxies within it.
What is a solar system?
Our sun has a latin name of Sol. From this, the term ‘solar’ has been derived, which is used to describe things that are related to the sun: hence, the solar system. The solar system describes the planets rotating around the sun. There are many stars in a galaxy, which means that there are also many solar systems. Planets have been discovered orbiting more than 3,200 different stars, at this point in time. We call these exoplanets, meaning the planets that are not in our solar system.Because there are trillions of galaxies within the universe, there is an almost countless number of solar systems within it.
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