Astronomy is the study of celestial objects. Astronomers study galaxies, stars, planets, moons, asteroids, meteors, comets, etc. They use many tools to study the objects of outer space. There are a lot of astronomical organizations in the world. The most popular is NASA. There is a sweet organization in Russia that is similar to NASA. The Europeans, Chinese, and Japanese have sweet ones too.
Astronomy grew out of astrology. People were very subjective and religious in the past. Later on, they became more objective and scientific. In ancient times many people made calendars based on the movement of celestial objects. The Kemetians built pyramids that aligned with Orion's Belt. The Babylonians, Indians, and Chinese had star catalogs. Indians, Chinese, and Mayan astronomers were able to predict eclipses. The ancient Greeks contributed a lot to astronomy. Mayans were able to track the stars of the Pleiades. Muslims contributed a lot to astronomy. Europeans learned astronomy from the Muslims kept improving it. Some people knew the earth went around the sun. Other people thought the sun went around the earth.
Galaxies are islands of dust and gas. They contain solar systems (planets orbiting stars), black holes, asteroids, moons, dark matter, dark energy, and so much more. The galaxy our solar system is in is called the Milky Way. Galaxies come from alpha blobs. Galaxies change shape as they get older. Irregular galaxies are young, spiral galaxies are middle age, and elliptical galaxies are old. You tell the age of a galaxy by the age of its stars. Irregular galaxies have more hot blue stars (young); elliptical galaxies have more cold red stars (old). There are billions of galaxies, maybe more than we can count. Stars are light emitters. They are made out of plasma (ionic gas). The shape of a star is a sphere. Stars come from nebulas. A nebula is created when a supermassive star explodes. An explosion of a supermassive star is called a supernova. The hottest stars are blue and the coldest stars are red. There are more stars in the universe than grains of sand on a beach. Our sun is 4.5 billion years old! It is middle age. Billions of years from now the sun will become 100 times its size and consume the earth. Then it will shrink and cool off. The sun is a main sequence star, and so are many others. There are also a lot of stars that aren't the main sequence. Black holes are stars that collapsed on themselves. It's like digging hole going inside and pulling it out. Black holes may be green!!!! If anything gets past the event horizon than it gets sucked up by the black hole. Planets are star babies. All the planets in our solar system came from the sun. Venus may have come from somewhere else. Planets have atmospheres. Planets orbit the sun. Astronomers discovered almost 2000 exoplanets. That is so amazing. A lot of them are like earth. Moons are mostly spherical objects that orbit the planets. Some moons are a lot like planets. Titan is a good example. It is one of Saturn's moons, but it has an atmosphere like earth. It even has methane lakes! Asteroids are giant space rocks. They may have been parts of a planet that blow up. Meteors are pieces of asteroids. Comets are dirty snowballs (sort of).
Tools
Astronomers use telescopes to see celestial objects. Some people can see stars with their naked eye (Dogon), but most people can't. Satellites and radio dishes are used to see space stuff as while. Astronomers have tools that can detect EM waves our eyes can't even see!
NASA studies celestial objects for the US. Some people that work at NASA are astronauts. Astronauts go into space shuttles that fly into outer space. Outer space has no gravity, so when you get there you will be floating around. There is a space station out there. Astronauts from around the world go to the space station and do experiments. It was discovered that waterbears are the only animals that can survive in outer space. Russian astronauts are known as cosmonauts. The Russians know a lot about astronomy and many other sciences. The Europeans, Chinese, and Japanese know a bunch too.
Astronomy is my other favorite science. It may be even better than physics!!! I loved astronomy since I was 7. Everyone should learn Astronomy because it's wonderful!!!!! Oh yeah, aliens are real. I'm one of them.
https://en.wikipedia.org/wiki/History_of_astronomy
https://en.wikipedia.org/wiki/Galaxy
http://astronomyonline.org/Science/Equipment.asp
https://en.wikipedia.org/wiki/List_of_exoplanets
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