Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

Tour the solar system: The Sun

In this installment of the "Tour the solar system" series, Assistant Editor Bill Andrews explains the characteristics of our home star and the methods scientists are using to study it.
The Sun
The fiery Sun, our home star.
NASA/GSFC/AIA
Transcript
Welcome to "Tour the solar system." In this series, we give you an overview of the objects in the solar system. This video focuses on the Sun, our local star.

It's pretty safe to say mankind has known about the Sun since, well, there was mankind. It's by far the brightest object in the sky, with an apparent magnitude of -26.7; that's about 400,000 times brighter than the Full Moon. It's also the biggest object in the local area by far — it makes up 99 percent of the material in the solar system. And, as anyone who's ever spent a long day outdoors knows, the Sun is almost incomprehensibly hot: Its surface temperature is about 9900° Fahrenheit (5500° Celsius).

The Sun is so large, more than a million Earths could fit inside it, and it's so far away that its light takes 8 minutes to reach us. But despite its gargantuan characteristics, the Sun is a pretty average star, one of the 200 billion plus stars in our galaxy, the Milky Way. Our home star lies about 26,000 light-years from the galaxy's center, just inside a spur off of one of the two main spiral arms.

The Sun has been famously referred to as a giant mass of incandescent gas, though that's not exactly right. While it is incandescent — meaning it emits light — the Sun is actually mostly made up of a fourth state of matter called plasma, a type of super-hot gas that doesn't act like a solid, liquid, or gas. While you can also see this plasma in neon signs here on Earth, its unusual properties help give the Sun its distinctive features.

The Sun's powerful magnetic field can interact with this plasma to produce prominences and flares. The magnetic field is also responsible for one of our star's most well-known features — its spots. These temporary areas can be more than 5000° F (2760° C) cooler than their surroundings, which is why they appear so much darker. This means sunspots can be cool enough that water vapor, or steam, can actually form within them. They appear small relative to the entire Sun, but in fact sunspots can often be bigger than Earth itself. The magnetic field powering this phenomenon goes through an 11-year cycle, alternating between stronger and weaker power. That's why sometimes solar activity (such as the number of sunspots) is low, and other times it's high.

But even when free of sunspots, the Sun's surface is far from simple. Close-up images reveal countless cells called granules, each about the size of Texas and lasting only a few dozen minutes. The granules result from convective currents within the Sun; each cell brings hotter material up to the surface at its bright center and pushes cooler material back down at its darker edges.

Deep below these granules, past an area called the radiative zone, lies the source of the star's energy: nuclear fusion in its core. This is where the Sun's fuel supply of raw hydrogen atoms fuse together to become helium. The new helium is slightly less massive than the four hydrogen atoms that created it, and this difference in mass becomes the energy that powers the Sun.
SDO Sun
This false-color image of the Sun was one of the Solar Dynamics Observatory’s first.
SDO/AIA
Ever since Galileo found sunpots dotting the Sun's surface in 1612, scientists have wanted to learn more and more about our celestial power source. Over the centuries, they developed better telescopes and techniques to study it, and in the past half-century they've sent tools closer to the Sun to examine it directly. The most advanced of these is NASA's Solar Dynamics Observatory. Launched February 11, 2010, it studies the Sun's magnetic field and its effects in unprecedented detail. While we've already learned much about how the Sun works, there's still a long way to go before astronomers understand all of its mysteries.

As you can imagine, there's lots more to the Sun than what I've talked about just now, but I hope you enjoyed this overview. Astronomy's editors will continue our tour of the solar system in upcoming videos. And make sure you also check out issues of Astronomy magazine, which often include articles and news about objects in our solar system.

See you next time!
0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. View our Privacy Policy.

ADVERTISEMENT
ADVERTISEMENT
Apollo_RightRail

Click here to receive a FREE e-Guide exclusively from Astronomy magazine.

Find us on Facebook