Earth and Moon. Image by: Eumetsat
Outer space is the void beyond any celestial body, such as planets and stars. There are only a few particles scattered here and there in space, whereas a cubic metre of the air we breathe on Earth contains millions of molecules.
Space is often called a vacuum because there’s hardly anything in it. Scientists think that space contains dark matter, but it’s really hard to detect so hasn’t been found yet.
Space Station. Image by: ESA/NASA
Scientists don’t really know exactly how big the universe is, but it’s pretty big! In the parts of the universe that we know about there are at least 170 billion galaxies, such as ours, the Milky Way.
Spectacular solar flare 17 July. Image by: ESA/NASA
Within galaxies there are Solar Systems, containing astronomical objects such as the Sun, stars and planets.
Everything is held together by gravity. Many people think that the universe originated during the Big Bang, where some really dense hot material has since continuously expanded and interacted, to form what we see today.
Andromeda Galaxy in infrared & X-rays. Image by: ESA / Herschel / PACS / SPIRE / J.Fritz
Just like there are different regions on Earth there are different parts of space, from geospace around the Earth, to intergalactic space between galaxies. There is no clear boundary between the Earth’s atmosphere and space and different scientists use different definitions.
The United States says that anyone travelling more than 80 km above the Earth is an astronaut! Just like there are laws on Earth that we have to follow, there are laws in space too. Nations can’t claim parts of space as their own, anyone can explore it, and it’s illegal to use nuclear weapons in space.
There’s loads of different research being done into all manner of space related topics. From volcanoes on Mars and the psychology of astronauts living and working in space, to designing solar sails to power spacecraft and the astrophysics of black holes.