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Artist illustration of the Milky Way. Image credit: NASA
Our Solar System is like a small oasis in our galaxy, which is an tiny island in the Universe. Understanding our Solar system, galaxy, and Universe, you need to know a few basic facts about the relative size of each. Here are quite a few facts about each. Hopefully, they will help you better understand the Universe around you.
Our Solar System is the smallest of the items in this article, so let’s start there. There are several ways to consider the size of the Solar System. I prefer to say it ends at the heliopause(the edge of the heliosphere). That is the end of the Sun’s influence on the interstellar medium and occurs at 90 AU in all directions. The heliosphere is not perfectly round, so the 90 AU is a give or take number. If you tried to put the size of the Earth in perspective, it would be about the size of a single peppercorn when compared to the Solar System. Scientists are just now getting their first solid data from the heliosphere. Voyager 1 and Voyager 2 are leaving the Solar System and continue return signals. No one is sure when the probes will cease to transmit.
The Solar System is just a tiny portion of the Milky Way galaxy. Our’s is a barred spiral galaxy and the Solar System is in a small spur off of one arm called the Orion Spur. There are 200 billion stars in the galaxy, but they are very far apart. The star closest to the Sun is in the Alpha Centauri system. That star is a short 4 light years, 37,842,921,890,323.2 km from ours. Just a short hop, skip, and jump from here in galactic terms.
That brings us to the Universe. The size of the Universe is impossible to calculate. Everywhere around us, the Universe is expanding and the distances to other galaxies are increasing. Current technology could never hope to measure many of the distances involved. That should change as the many types of telescopes and branches of astronomy become more advanced.
Here’s an article about the ring of stars discovered around the Milky Way, and another about how astronomers measure its thickness.
Here’s more information about the Solar System from Views of the Solar System. And here’s more from SEDS.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.
References:
NASA: Distance to the Heliosphere
NASA: Milky Way Galaxy
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