Astronomy_shs4

=
Our Universe started out in nothing and exploded into the beginning of our Universe in what scientists call the Big Bang. 15 billion years ago, our Universe exploded from nothing. Our Universe started small and expanded rapidly. It was initially a mixture of matter, antimatter and radiation, but as temperature cooled protons and neutrons formed. Eventually, they cooled enough that atoms started forming, mainly Hydrogen and Helium. As the Universe expanded matter clumped together and eventually gravity collapsed the matter and galaxies formed. =====

=
=====

=
Galaxies formed after the Universe had formed. Galaxies formed 3 billion years after the Big Bang. There are 3 types of Galaxies, elliptical, spiral and irregular. When galaxies merge together, they cause spiral arms. Our galaxy, The Milky Way, may collide with the Andromeda galaxy. =====

=
=====

=
The Milky Way is a galaxy that has a unique structure. On the outside layer is the disk. Inside of the disk is the layer of gas and dust. In the middle of the disk and gas and dust is the central bulge. The central bulge consists of the oldest stars in the galaxy. Four spiral arms spread out from the central bulge. =====

=
The Milky Way has an interesting rotation. The Milky Way’s rings spin clockwise. The planets spin counterclockwise. Our sun spins around the central bulge while we spin around our sun. Earth spins sideways and towards the sun which forms a circular movement around the sun. =====

=
=====

=
Planets formed after the Big Bang. The sun formed when gravity pulled together dust and particles. The sun made a disk and solid materials came together and formed bigger clumps.The four biggest masses were planets and grew disks of their own where moons could form. The planets could later hold gas. The planets were heated by collisions while also heated by radioactivity. The lighter dirt rose to the top while the metal sunk to the middle and then solidified. =====

=
Moons, Rings, and Comets were formed after planitesimals started sticking together and forming larger masses. When a comet chills and heats up near the sun, it becomes a comet. Our moon formed when a collision happened between our earth and a planet the size of Mars. =====