Some Solar Statistics
Published on May 25, 2006 at 6:25 pm.
4 Comments.
Filed under Sun.
The Sun is big. It’s bright, too. But, how big and bright is it? Very! Well, the astrophysicist in me wants numbers! I know that at least a few of my readers also like to put numbers to things. So here are some solar statistics for you.
The Sun has a mass of 1.99×1030kg and a radius of 6.96×105km. OK, so what? Let’s put this into perspective. This means that the Sun has a mass of 330,000 Earths. You could line up 109 Earths across the Sun, from one side to the other. Well, volume goes as the cube of the radius, so that means that you could fit 1,300,000 Earths inside of the Sun. Well, more or less, that is. The Sun is really just a giant ball of hot gas, so it doesn’t really have a surface (see my post about the Earth’s atmosphere from yesterday). So the numbers for physical size of the Sun are sort of an estimate. This “edge†of the Sun is defined by where the Sun gets thin enough and cool enough for light to begin to shine through its gasses.
Speaking of light, the Sun is pretty bright. The Sun shines with a light output of 3.85×1026 Watts. That means that each square meter of the Sun’s surface shines as brightly as just over one million 60 Watt light bulbs! Wow. Now, aren’t you glad that you don’t have to foot the bill for that! Here in Texas, where the electric rates are among the highest in the nation, that means that you’d have to pay $213,000 per day just to light that one meter of the Sun’s surface!!!! (That is computed using the electric rates on my electric bill that I just got last week.) And, of course, the Sun has a LOT of square meters of surface area!
Well, that other numbers can we get from this data? Well, we know that the Sun is composed of 91.2% hydrogen and 8.7% helium (by number of atoms). You will normally see in textbooks that the Sun is 71% hydrogen and 27% helium, but that is by mass. Remember that helium has about four times the mass of hydrogen. Well, this means that if you do a little mathematics, the Sun has roughly 9.3×1056 atoms in it!
You’ll notice that I am using scientific notation a lot here. That is because these numbers are just too ridiculously huge to write out otherwise. People often toss around the term “astronomically big number†without having a clue what an astronomically big number really is. The students in my introductory astronomy course for non-majors are simply shocked when they see these huge numbers all over the place. Even the majors’ students are a bit overwhelmed when it sinks in how big these numbers are that we are working with.
Let’s see. What else can we figure? Well, if you know the mass and radius of an object, you can compute the acceleration of gravity at its surface. Using the appropriate formula on the Sun, we find that at the Sun’s “surface†the gravity is roughly 28 times that of Earth. In other words, you’d feel like you weighed 28 times more on the surface of the Sun than you do on Earth. Well, you wouldn’t feel it for long. First, that level of g-force would make you black out instantly, and would kill you soon after. That would be merciful, though, since if you were on the surface of the Sun, you’d burn up in just about no time, flat. Oh, well.
Overall, the Sun has a density of about 1.4 grams per cubic centimeter. This is roughly ¼ of the density of Earth, though it is in the ballpark of the density of planets like Jupiter or Saturn. Now, this is the overall density. As you get closer to the center of the Sun, it gets denser. At the center of the Sun, the density of the Sun is roughly 160 metric tons per cubic meter. This works out to be about 0.16 kilograms per cubic centimeter. Let’s put this in perspective. Lead is famous for being heavy. This is about 14.2 times the density of lead. People don’t think about it, but gold is actually more dense than lead (and prettier). The center of the Sun is 8.3 times denser than pure gold.
The Sun’s a long way from Earth, too. The Sun is about 1.5×108 km from Earth. That means that you could put about 108 Suns side by side between the Sun and the Earth, or just under 11,800 Earths side by side. We call the average distance between the Earth and the Sun an astronomical unit.
So, there you have a few solar statistics. I could go on, but this gets the idea of how big the Sun is compared with Earth.
-Astroprof
Ray on February 4, 2008 at 8:05 pm: 1
How long does it take for the sun to set, from the time the first lower “edge” hits the horizon until the upper “edge” disappears? I think this is the same as asking, for an observer on earth, how long does it take for the sun to move its own width?
Thank you!
Astroprof on February 4, 2008 at 10:35 pm: 2
Ballpark figure is about two minutes.
Gordon on April 26, 2008 at 12:32 am: 3
pretty easy to calculate… the tangent of the arc subtended by the sun is 109/11800, according to the numbers in the article. Your calculator will tell you that corresponds to a subtended angle of .53 degrees. The earths angular rotation rate is 15 deg / hour so it takes .035 hours or 127 seconds
Astroprof on April 26, 2008 at 3:45 pm: 4
It is a little tougher than that. You really need to include atmospheric effects. But, it is a little over two minutes, as noted.