XThe electromagnetic spectrum is huge. We are aware of the very small part of it we call light, which is most of what gets through our atmosphere. But above the atmosphere, we are bathed in radio waves, infrared, visible light, ultraviolet, and x-rays, all of which are part of the electromagnetic spectrum. Since we have become able to put telescopes above the atmosphere, all of these parts of the spectrum have become accessible to astronomers.

Repeated images of the sun in x-ray wavelengths.

Repeated images of the sun in x-ray wavelengths. Source

The shorter the wavelength the more energetic the light, and the sun’s outer atmosphere, the corona, is both the hottest part of the sun and the part most visible in x-rays.

It is also the wavelength which changes most over the solar cycle, which has major effects on auroras, communications, electrical power grids, and low-earth satellite orbits. The sunspot cycle may also affect weather. The Maunder minimum, a period of low sunspot activity around 1645-1715, is often cited as one possible cause of the Little Ice Age.

Pussy WillowsWe now have x-ray images of the sun through the solar cycle, so we can see how variable the outer atmosphere of our sun really is.

That sun rose this morning at 5:28 and will set 16 hours and 43 minutes later at 10:11 this evening. Nautical night (sun more than 12° below the horizon) has followed astronomical night, though we’ll still have nautical twilight until May 17. It’s warmed up quite a lot the last week, and nighttime temperatures are now only a little below freezing. The remaining snow is melting fast; my yard is almost more lake than snow. And the pussy willows are blooming!