The average depth of the oceans on Earth is a little more than two miles. And the greatest depth is about seven miles. But thats little more than a big puddle compared to the ocean on Ganymede, the b

Astronomers use many techniques to find planets in other star systems. One of those is looking where there doesnt appear to be anything wide gaps in disks of dust around young stars. Most of these

The Vikings liked to see the world. For a couple of centuries, they plied northern oceans, exploring much of Europe, establishing colonies in Greenland, and even reaching North America. They did so wi

We can never just look up in the sky, point to one of the dots of light there, and say, Oh, yeah thats Neptune! Although its the fourth-largest planet in the solar system, Neptune is so far that

Youve probably never seen two donkeys perched on the back of a crab. Unless, that is, youve spent much time looking at the stars. Two faint stars in Cancer have names that mean the northern and sout

Most stars begin their lives in colorful style inside giant, glowing clouds of gas and dust. One example is the Rosette Nebula, which looks like a delicate rose. Its in Monoceros, the unicorn. The

The celestial unicorn isnt much to look at. Monoceros fills a void between the bright constellations Orion, Gemini, and Canis Major and Canis Minor. Yet you need dark skies to see even a smattering o

In the mid 1860s, astronomers were just beginning to use a new tool to study the heavens. Called spectroscopy, it allowed them to split the light from an astronomical object into a rainbow of colors.

Astronomers have discovered dozens of planets that orbit both stars in a binary system. Like Tatooine of Star Wars fame, that gives the planets double sunrises and sunsets. But only a handful of tho

Many spacecraft bounce among the planets and moons of the solar system like theyre inside an old pinball machine. They use the gravity of one object to bat them toward another. Thats like having an