This column was provided by San Benito County resident and amateur astronomer Ron Martin as part of a local series on astronomy. Lea este articulo en español aqui.
We all live in the Milky Way Galaxy, a spiral-shaped galaxy. A spiral-shaped galaxy is a massive system of stars, gas, and dust that often resembles a giant, rotating pinwheel. It is a massive collection of 300-400 billion stars, gas, and dust, and our solar system is located roughly halfway out from the center, on one of the smaller spiral arms known as the Orion Arm. The name “Milky Way” comes from the ancient Greek and Latin terms for “road” or “river of milk,” inspired by the hazy, milk-white band of stars visible to the naked eye across a dark night sky. When you look up at the night sky on a clear, dark summer evening away from city lights, the faint cloudy band stretching across the horizon is actually the combined light of billions of individual stars and cosmic dust clouds within our own galaxy.
The Sun, our star, lies roughly 27,000 light-years away from the center of the galaxy, in a partially formed arm known as the Orion-Cygnus Arm, which itself lies about midway between the two main arms. This places us about midway between the center and the edge of the galaxy, in what might be considered the Milky Way’s suburbs. Just as Earth orbits the sun, our solar system orbits the center of the Milky Way. Despite hurtling through space at speeds of around 515,000mph, our solar system takes approximately 250 million years to complete a single revolution. The last time our planet was in this position, dinosaurs were just emerging and mammals were yet to evolve.
As you know, the Milky Way is shaped like a spiral, with beautiful swirling arms. Very similar to the Pinwheel Galaxy (this photo I took this winter). It has four major arms: the Perseus Arm, the Scutum—Centaurus Arm, the Carina-Sagittarius Arm, and the Orion Arm, which is where our Solar System is located. If you could take a spaceship far enough, you would see the Milky Way as a flat disk with a bright center, known as the Galactic Bulge.
This bulge is surrounded by a much fainter halo of stars and globular clusters. In terms of size, the Milky Way is about 100,000 light-years across. Imagine that, a single light beam from one side would take 100,000 years to reach the other side. Wow! Not only does our galaxy contain stars, but it also hosts nebulae, supernova remnants, and much more, making it a fascinating place for scientists to study.
The current thinking is that the Milky Way started life some 13-14 billion years ago, or about a billion years after the Big Bang. It began when a cloud of gas and dust collapsed to form a huge sphere. Over time, the sphere continued to gain mass until it began to spin, which in turn caused it to flatten into a disc.
Unfortunately, it’s not possible to see the center of the Milky Way with just your eyes – there’s just too much gas and dust in the way. However, you can confidently gaze skyward and know that you’re also looking toward the heart of our galaxy. The Milky Way appears most densely in Sagittarius, the Archer, a southern constellation that’s best seen in the summer months from the northern hemisphere. The brightest stars of Sagittarius form a pattern that resembles a teapot, with a cloud of steam apparently emanating from the spout. When you look toward this steam, you’re looking across 27,000 light-years of galactic space, filled with billions of stars and planets, toward the center of the galaxy.
Fun facts:
The Name: The Greeks and Romans thought the faint, cloudy band of light across the night sky looked exactly like milk spilled across the heavens!
Giant Pinwheel: The Milky Way is a barred spiral galaxy, meaning its stars are gathered into flat arms that spin around a bright, bulging center.
Cosmic City Address: Our Solar System lives in one of the Milky Way’s outer spiral arms, about halfway from the center.
Long Rides: Just as Earth orbits the Sun, the Sun orbits the center of the Milky Way. It takes our entire solar system about 250 million years to travel around the galaxy just once!
A Monster in the Middle: At the very heart of our galaxy sits a supermassive black hole named Sagittarius A.
Galactic Neighbors: We have a close neighbor called the Andromeda Galaxy.
It is moving toward us, and in about 3.75 billion years, the two galaxies will meet and blend!
In terms of size, the Milky Way is about 100,000 light-years across! Imagine that: a beam of light from one side would take 100,000 years to reach the other side. Wow! Not only does this galaxy contain stars, but it also hosts nebulae, supernova remnants, and much more, making it a fascinating place for scientists to study.
To catch a glimpse of the stunning Milky Way, you need to find a dark spot away from city lights. The best time to see the Milky Way is during the summer months, when nights are warm and clear. If you live in a city, consider traveling to the country, where there’s less light pollution. Once you’re in a good spot, let your eyes adjust to the darkness! This can take around 20 minutes. Avoid using bright lights, as this can interfere with your night vision. Use a red flashlight instead—red light is less harsh on your eyes. When the time is right, look upward: you should see that beautiful, hazy band stretching across the sky.
You can also bring binoculars or a telescope to take a closer look at stars and other celestial objects. If you’re lucky, you could spot the Andromeda Galaxy, star clusters, or even planets like Jupiter and Saturn! Take your time and enjoy the view because the Milky Way is a reminder of how vast and beautiful our universe is!
Have fun and keep looking up.
Signing off
Ron Martin
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