We have barely passed the equinox, but it already feels like we are heading into summer. I think another few feet of snow would be great, but in the mean time I hope you are taking advantage of the warmer evenings to get outside.
Spring is usually galaxy season for amateur astronomers with a telescope. But whether you like to look at galaxies, stars or emission nebulae, almost everything you are looking at is hydrogen.
Hydrogen is the simplest and the most common element in the universe. It is made from just one proton and one electron. In terms of number of atoms, almost 90 percent of the matter in the universe is hydrogen. Most of the rest is helium, and everything heavier makes up only a tiny fraction of the “normal” matter. Dark matter and dark energy may make up more “stuff,” but you won’t see those while standing in your backyard.
An emission nebula, such as M8, the Lagoon Nebula, or M42 in Orion’s sword, is made of hydrogen as a low-density gas. In these glowing interstellar clouds, the hydrogen is lit up by nearby, very hot stars. If you send the light from one of these hydrogen clouds through a prism, instead of a rainbow, you will see the very distinct and unique spectral lines that identify the gas as hydrogen. (Or whatever other elements might be there.)
The hydrogen spectrum is easy to recognize – one very intense red line, a much dimmer cyan line and a few even dimmer blue lines. The overall color is sort of magenta – mostly red with a hint of blue in it. Unfortunately, your eyes are not sensitive enough to see colors in things this dim. So through a telescope, a hydrogen emission nebula usually just looks a ghostly gray.
When you see a star, you are looking at more hydrogen. The radiated energy is from hydrogen fusing into helium. The spectrum is different from the low density clouds, though. Stars, and any other hot dense objects, will radiate their energy in a broad spectrum. This light will make a full rainbow when sent through a prism.
Jupiter also is mostly hydrogen. It is still dominating the evening sky in Gemini, but that light is just reflected sunlight.
Mars will be making its closest approach to Earth on April 8, but any time this month is a good time to see it. The red planet rises just after dark near the star Spica in the constellation Virgo. Mars, like Earth, is too small and close to the sun to keep much gaseous hydrogen around. Earth has lots of hydrogen, but it is attached to molecules with heavier atoms, such as oxygen to make water.
Celebrate tax day by watching the total lunar eclipse. If it is clear April 15, you should get a good view.
Thanks to everyone who noticed the missing factor of a million in the distance to M82 last month. I do appreciate the feedback. (What’s an extra six zeroes in such a mind-boggling distance?)
firstname.lastname@example.org. Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.