However, the existence of these arms has been determined from observing parts of the Milky Way – as well as other galaxies in our universe. As these density waves move through an area, they compress the gas and dust, leading to a period of active star formation for the region. stars and clouds of gas clustered together. The spiral arms are formed from density waves that orbit around the Milky Way – i.e. For the longest time, the Milky Way was thought to have 4 spiral arms, but newer surveys have determined that it actually seems to just have two spiral arms, called Scutum–Centaurus and Carina–Sagittarius. If you could travel outside the galaxy and look down on it from above, you’d see that the Milky Way is a barred spiral galaxy. It measures 220,000 light years in diameter, and has an estimated 400-800 billion stars within it. Andromeda, the closest major galaxy to our own, is about twice as large as our own. And our galaxy has consumed others in its long history, such as the Sagittarius Dwarf Galaxy.Īnd yet, our galaxy is only a middle-weight when compared to other galaxies in the local Universe. In fact, the Canis Major Dwarf Galaxy is the closest galaxy to the Milky Way because its stars are currently being added to the Milky Way’s disk. It became its current size and shape by eating up other galaxies, and is still doing so today. Since one light year is about 9.5 x 10 12 km (9.5 trillion km) long, the diameter of the Milky Way galaxy is about 9.5 x 10 17 to 11.4 x 10 17 km, or 9,500 to 11,400 quadrillion km. Size of the Milky Way:įor starters, the Milky Way is really, really big! Not only does it measure some 100,000–120,000 light-years in diameter and about 1,000 light-years thick, but up to 400 billion stars are located within it (though some estimates think there are even more). But thanks to ongoing efforts, astronomers now know where our Sun resides in the galaxy. And given that we are embedded within it, it has been historically difficult to ascertain our exact position. In truth, we’ve only been aware of the fact that we are part of a much larger disk of stars that orbits a common center for about a century. Much the same is true about our Solar System’s position within the Milky Way. It was only after many centuries of continued observation and calculations that we discovered that the Earth (and all other bodies in the Solar System) actually orbits the Sun.
This perception was due in part to the fact that Earth-based observations were complicated by the fact that the Earth is embedded in the Solar System. For thousand of years, astronomers and astrologers believed that the Earth was at the center of our Universe.
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