The Sun and Comparison to Other Stars

Size The volume of the sun is 3.38 x cubic miles. This means it would be possible to fit 1,300,000 earths inside the sun. Now this may seem big, but take a look at this…

] This is the sun next to much larger stars. In this scale, Jupiter would be approximately 1 pixel! That’s Jupiter!

Composition The sun is made up of hydrogen, helium, and less than 1% of oxygen, carbon, neon, nitrogen, magnesium, iron, and silicon.

Composition of Other Stars Every star that is formed in the Milky Way galaxy is made almost only of hydrogen and helium. On average, 71% of a stars’ mass is hydrogen, and 27% is helium. The other 2% is heavier elements.

Hertzsprung-Russell Diagram A Hertzsprung-Russell (HR) Diagram is a chart that shows both spectral class (color) and absolute magnitude (actual brightness) of stars. Some, like this one, also show temperature (Kelvin) and luminosity (brightness compared to Sun).

H-R Diagram with Stars Labeled

Absolute Magnitude ‐ Absolute magnitude is how bright an object would appear at 10 parsecs (1 astronomical unit) from the viewer. ‐ The absolute magnitude of the Sun is about ‐ Most stars have an absolute magnitude between -10 and +17. ‐ The closer the absolute magnitude to zero, the brighter the star. Arcturus has the closest absolute magnitude to 0 known to man.

Apparent Magnitude ‐Apparent magnitude is how bright an object is regardless of the distance from the viewer. ‐The apparent magnitude of the Sun is about as seen from Earth. ‐Most stars have an apparent magnitude between -40 and +40. ‐Vega was chosen to be the reference for all other stars, and was given an apparent magnitude of 0. ‐Sirius is the brightest star seen from Earth (except the sun).

Spectral Type (Classification) Spectral type is simply the color of a star. The letters O, B, A, F, G, K and M each correspond to a color. O, B and A are blue, F is bluish- white, G is yellow, K is orange, and M is red. The Sun is a type G star. An easy way to remember these letters is as follows: “Oh, Be A Fine Girl, Kiss Me.” O B A F G K M

Temperature The surface temperature of the sun is about 5,800 K (10,000 degrees F). The core can reach over 15 million K (27,000,000 degrees F).

Surface Temperature of Other Stars Most stars are between 3,000 and 30,000 K (5,000°F and 54,000°F). Blue hypergiants are the hottest stars. Brown dwarfs are the coldest. The sun is a G-type main sequence star, often improperly called a yellow dwarf because g-type stars are actually white.

Luminosity Luminosity on an H-R D Diagram is the brightness of an object compared to the sun (Sun=1).

Solar Eclipse A solar eclipse occurs when the moon passes between the sun and the moon. The moon blocks the light coming directly from the sun (umbra), and all that is visible is the light that surrounds the moon (penumbra).

Ultraviolet This is an ultraviolet picture of the sun. Ultraviolet cameras allow us to see the UV waves that the sun releases as they are otherwise invisible.

Sunspots Sunspots are spots on the sun caused by powerful magnetism. This magnetism causes cooling on a particular spot on the sun’s surface, giving it a darker color.

Solar Flares Solar flares are also caused by magnetic forces within the sun. When magnetic activity increases, eruptions occur, and the gases jump off of the surface, resulting in a flare of solar gases. These flares can be fairly small, or massive, as shown below….

Stellar flares occur on stars. Scientists have detected a flare so large, that had it occurred on the sun, a mass extinction would’ve occurred on Earth. This is an illustration of Swift, the telescope that detected this massive solar flare.