Are Sunspots Really Black?

Are the sun's spots really black? I mean in NASA's pictures the sun is always colored in yellow or orange while it is in fact close to pure white. Are we being deceived again with black sun's spots? If they are truly black then they must be very cool like no more than 700K otherwise they would start to glow. I really wish the NASA would stop messing around with colors and show us how the sun and the planets really look like.
- Anonymous

You're right, sunspots aren't really black, and they definitely aren't cold. According to , "If you were to put a sunspot in the night sky, it would glow brighter than the full moon with a crimson-orange color!"

The surface of the sun is about 5,700 K. Sunspots are cooler, between 3,000 K and 4,500 K. The intensity of a hot object is proportional to the fourth power of its temperature, so sunspots are dramatically dimmer than the surrounding material even though they're only moderately cooler. They appear dark in contrast to their surroundings, even to the human eye. For example, if you view a , any sunspots will look dark against the rest of the sun. (Don't look directly at the sun through a telescope or anything else without a safe solar filter.)

I can think of a few goals when deciding how to present an image:

1. Displaying data. Astronomical images (like awesome daily images of the sun) are usually taken with filters that transmit particular wavelengths of light, which can help map out the distribution of different elements. Some of these wavelengths might not even be visible light, so the only way to visualize them is with false color. Other scientific images are processed to enhance contrast or make subtle features more visible. Part of the role of science is to show us what we can't see with our eyes alone.
2. Accuracy. Part of the role of science is also to show us what things really look like, such as the . 
3. Art. As , he colors images of the sun orange because "I like it." The Hubble Space Telescope can't take color pictures—it takes monochrome images with different wavelength filters, which are more useful for research. But researchers also  to those filters and combine them to create beautiful photos, because they inspire people to be interested in the universe (and maybe to support funding for expensive telescopes).

Seeing a true-color image of the sun could make someone more curious about science, too. Anyone who creates an image has to decide how to balance these three goals.

Rebecca Holmes

(published on 01/21/2015)