Dark energy and dark matter make up about 96% of the universe. Baryonic matter, the stuff of stars, planets, you and me, makes up only 4% of the universe. And most of that isn’t actually in stars and planets and us, but between the vast expanse of galaxies. It makes up the intergalactic medium (IGM) and it is notoriously difficult to observe.
Astronomical Units
Thanks to a rare alignment of planets 250 years ago, we were able to learn for the first time just how large our solar system really is.
Blood Moon
This week those of us in the western hemisphere will have the chance to observe a lunar eclipse. It will happen in the evening/morning of April 14/15, reaching peak darkness at about 3 a.m. EDT (0600 GMT). Depending on the darkness of your sky, the Moon may be invisible to the naked eye, or it may appear as a dark, blood moon.
Parallax View
How is it possible to say with confidence that one star is 8 light-years away, while another is 640 light-years away? There are actually several methods to determine cosmic distances, and these are combined to create what is known as the cosmic distance ladder, but the oldest and most direct method uses the property of parallax.
Sunrise, Sunset
We live on a small rock racing through space. And our days are marked by the rising and setting of a star.
Beyond the Farthest Star
When you look up into the night sky, you are seeing into the past. Cosmic distances are so vast that it takes time for light to travel them. The brightest star in the night sky is Sirius, more than 8 light-years away, which means we see Sirius not as it is now, but as it was 8 years ago.
Hot Rocks
Asteroids come in a range of sizes, from hundreds of kilometers in diameter down to a meter wide and smaller. Determining just how many asteroids there are is a challenge, because the smaller an asteroid’s size, the more difficult it is to observe.
A Blanket Full of Sky
If you hang around astronomers for a while, you will soon hear about the problems of light pollution. Light pollution is one example of the challenges of Earth-based astronomy. Specifically the atmosphere that surrounds our planet.
What You Get is What You See
These images look very different from each other because they were observed by different instruments, that each detect different ranges of wavelengths of light. Just as our eyes are capable of observing a particular range of wavelengths, each instrument can only observe a particular range of wavelengths.