Astronomy Overview: Galaxies and Stars

Galaxies

• Galaxies are vast collections of stars, gas, dust, and dark matter.
• Our galaxy, the Milky Way, is a spiral galaxy with a central bulge and spiral arms.
• Other galaxy shapes include elliptical and irregular.

Nebulae

• A nebula is a cloud of gas and dust in space.

Solar System

• The Solar System is located in one of the Milky Way's spiral arms.
• The Solar System contains eight planets, dwarf planets, moons, asteroids, and comets.

Constellations

• Ursa Major (the Great Bear) and Ursa Minor (the Little Bear) are two famous constellations.
• Polaris, the North Star, is located at the end of the handle of Ursa Minor.

Stars

• Stars are celestial bodies of hot, glowing gas that produce energy through nuclear fusion.
• Stars produce light and heat.

The Sun

• The Sun is a star at the center of our Solar System.
• The Sun is composed of three main parts: the core, the mantle, and the atmosphere.
• The core is where energy is produced through nuclear fusion.
• The mantle transports energy from the core to the surface.
• The atmosphere is the outer layer of the Sun and is divided into the chromosphere, photosphere, and solar corona.

Inner Planets

• The inner planets are Mercury, Venus, Earth, and Mars.
• These planets are primarily composed of rock and metal.
• Mercury is the smallest and closest to the Sun.
• Mercury has no atmosphere and is heavily cratered.

Outer Planets

• The outer planets are Jupiter, Saturn, Uranus, and Neptune.
• These planets are primarily composed of gas and ice.
• Uranus is the third largest planet and the coldest.
• Uranus has rings and satellites.

Dwarf Planets

• Ceres, Pluto, and Eris are dwarf planets.
• Ceres is the smallest dwarf planet and was previously thought to be the largest asteroid.

Celestial Bodies

• Satellites are objects that orbit planets.
• Comets are icy bodies that orbit the Sun.
• Asteroids are rocky bodies that orbit the Sun.
• Meteorites are small fragments of rock or metal that enter the Earth's atmosphere, sometimes leaving trails called meteors.

Galaxies

• Consist of millions of stars and nebulae
• Galaxies exist in different shapes: spiral, elliptical, and irregular
• Our galaxy is called the Milky Way
• The Milky Way is a spiral galaxy with a central point and arms
• The Solar System is located on one of the arms of the Milky Way

Constellations

• Two famous constellations in the Solar System are Ursa Major and Ursa Minor
• Ursa Minor has seven stars, including the Polar Star, the brightest star in the constellation

Stars

• Stars are celestial bodies of gas that produce heat and light through nuclear fusion

The Sun

• Composed of three parts: the core, the mantle, and the atmosphere
• The core is the center of the star where energy is generated
• The mantle surrounds the core and is where energy is transported to the surface
• The atmosphere is the outer part of the star, divided into the chromosphere, photosphere, and solar corona, from inside to outwards

Inner Planets

• The inner planets are Mercury, Venus, Earth, and Mars
• All are solid, with a crust and an iron core
• Mercury is the closest to the Sun and the smallest
• Mercury has no atmosphere, allowing meteorites to collide, creating craters on its surface

Outer Planets

• The outer planets are Jupiter, Saturn, Uranus, and Neptune.
• Uranus is the third largest and coldest planet, with a blue color
• Uranus has satellites and rings

Dwarf Planets

• Dwarf planets include Pluto, Ceres, and Eris
• Ceres, previously thought to be the largest asteroid, is the smallest dwarf planet

Celestial Bodies

• Celestial bodies include satellites, comets, asteroids, and meteorites
• Meteorites are small rocks that are not classified as asteroids or comets
• Meteorites can collide with other celestial bodies, creating craters, like those found on the Moon