The Sun and the Moon

About This Photograph

Here we see an interesting study in differences and similarities. On the left is our Sun, seen here in a specific wavelength of light emitted by hydrogen gas. This allows us to see the intricate details on the surface and the prominences extending from the edge of the sun out into space. On the right is Earth's Moon, our closest celestial companion.

In many ways, these two objects couldn't be more different. The sun is a seething ball of gas, powered by nuclear reactions in a central core with a temperature of over 10 million degrees Kelvin. Its appearance changes day by day and even minute by minute as the gas near the surface is churned by the intense heat within. The moon is comparatively frigid and static. The same side of it always faces us, and its appearance is virtually unchanging except for the phases it displays as it is lit up by the sun from different angles.

As different as they are, from our perspective here on Earth, there is one striking similarity. Even though the diameter of the sun is about 400 times that of the moon, and it out-masses the moon by about 27 million times, they are both approximately the same apparent size in our sky, as pictured here. This happy coincidence is what makes it possible for us to observe total solar eclipses. If the conditions are right, the entire disk of the sun is just covered by that of the moon, blocking the bright light of the solar photosphere, but still allowing us to observe the sun's prominences and corona.