Image Credit: Sombrero Galaxy Messier 104 - NASA/STScI/AURA
Galaxies are systems of millions or billions of stars, together with gas and dust, held together by gravitational attraction. While estimates among different experts vary, most agree that there are somewhere between 100 billion and 200 billion galaxies.
Image Credit: R. Hurt (SSC), JPL-Caltech, NASA
The Milky Way Galaxy
Our Milky Way is a spiral galaxy containing 400 billion stars bound together by gravity. From Earth, the galaxy has the appearance of a faintly luminous band in the sky. The Milky Way is the home galaxy of Earth and our Solar System.
Image Credit: NASA/JPL-Caltech/T. Pyle (SSC)
Our Solar System
A solar system refers to a star and all the objects that travel in orbit around it. Our solar system consists of the sun - our star - eight planets and their natural satellites (such as our moon); dwarf planets; asteroids and comets. Our solar system is located in an outward spiral of the Milky Way galaxy. The Sun is the power plant that drives the Solar System. Its immense gravity holds the planets in orbit. Its energy drives weather systems on the planets with atmospheres.
Image Credit: SDO x4 point 9 solar flare February 24 2014 – SDO
The Sun and Stars
The Sun is one of more than 100 billion stars in the Milky Way. Stars come in different sizes, colors, and temperatures. A star is a huge ball of gas held together by gravity. The center of a star is extremely hot and produces energy. Some of this energy is released as visible light, which makes the star glow. Our Sun lies at the heart of our solar system, where it is by far the largest object. It holds 99.8 percent of the solar system's mass and is roughly 109 times the diameter of the Earth - about one million Earths could fit inside the sun.