The Milky Way is the galaxy that contains our Solar System. The name "Milky Way" comes from its appearance as a dim glowing band arching across the night sky, in which the unaided eye cannot distinguish individual stars.

Size and Shape

The Milky Way is a barred spiral galaxy, meaning it has a central bar-shaped structure composed of stars.

• Diameter: The latest estimates suggest the diameter of the Milky Way is between 100,000 and 200,000 light-years.
• Thickness: At the center, the bulge is roughly 12,000 light-years thick. The disk of the spiral arms is much thinner, about 1,000 light-years thick.
• Spiral Arms: The Milky Way has four major spiral arms and at least one arm that is partially-formed. Our Solar System is located on a minor arm, called the Orion-Cygnus Arm, situated about 25,000 to 28,000 light-years away from the Galactic Center.

Stars and Mass

The sheer scale of the Milky Way is difficult to comprehend.

• Number of Stars: It is estimated to contain between 100 billion and 400 billion stars.
• Mass: The total mass of the Milky Way is estimated to be about 1.5 trillion times the mass of the Sun. About 90% of this mass is thought to be Dark Matter, an invisible substance that does not emit or absorb light.
• Age: The oldest stars discovered in the Milky Way are nearly as old as the universe itself. The estimated age of the galaxy is approximately 13.6 billion years.

Galactic Center

At the very heart of the Milky Way is an intense and energetic region.

• Supermassive Black Hole: The Galactic Center hosts a supermassive black hole known as Sagittarius A* (pronounced "A-star").
• Mass of the Black Hole: Sagittarius A* has a mass about 4.3 million times that of the Sun.
• Location: While we cannot see the black hole directly, its location is known to be in the direction of the constellation Sagittarius.

Galactic Movement and Future

The Milky Way is not stationary; it is constantly moving through space.

• Solar System Orbit: The Sun and the entire Solar System orbit the Galactic Center at an average speed of about 514,000 miles per hour (828,000 km/h). Even at this speed, it takes roughly 230 million years for the Sun to complete one orbit, which is known as a cosmic year.
• Collision Course: The Milky Way is currently on a collision course with its nearest major galactic neighbor, the Andromeda Galaxy. This event is expected to occur in approximately 4.5 billion years. The resulting new galaxy has been nicknamed "Milkomeda."

Interesting Facts

Here are some additional facts about our galaxy: