Gravity is anything but elementary. Explore the ongoing investigation of gravity, and meet astrophysicists struggling to capture its most elusive hallmark: the gravitational wave.

Peer at the world through Einstein's eyes—a scientist who saw a beam of light and imagined riding it, a self-proclaimed "citizen of the world" who spoke out on global issues from pacifism to racism.

We owe our lives to gravity. It holds the atmosphere to Earth and keeps us all from falling off into space. Not to mention that without gravity, the stars and planets—including Earth—wouldn't even exist!

In three billion years, our Milky Way Galaxy will collide with its nearest neighbor, the Andromeda Galaxy. See how these two spiral galaxies are expected to merge, forming an elliptical galaxy.

Since 1995, astronomers have discovered more than 100 planets orbiting stars beyond our Sun—only a fraction of those thought to exist. Take an interactive tour of the Milky Way Galaxy to visit these "exoplanets."

What happened after the Big Bang? This comic strip explains the interactions that lead to the creation of stars, planetary nebulas, and supernovas.

Don't miss the latest spectacular images from observatories around the world and in space. Visit our weekly Astro Snapshot for new sightings in our observable universe.

For every visible star in the observable universe, there are nine masses that are invisible and unidentified. Learn more about the astronomer who proved the existence of dark matter.

Telescopes capture the Sun's ultraviolet light as beautiful images that are full of information about solar processes. This spectacular interactive photo gallery portrays the turbulent Sun in action.

Talk about a long-term power source. For billions and billions of years, the Sun has been giving off energy that equals 4 x 10²⁶ watts. What keeps the Sun burning so bright?

The Sun continuously sheds its skin, blowing a fierce wind of charged particles in all directions. Find out what happens when this wind—carrying mass from a solar storm—slams into Earth.

We see only a fraction of the stars in our Milky Way Galaxy when we gaze at the night sky. Find out why the stars that appear brightest to us are not necessarily the closest to Earth.

There are thousands of stars in the night sky. Hidden among them are constellations and planets. How many can you find? Record your sightings in a stellar sky journal.

What are the stars made of? At 25, Cecilia Payne answered this fundamental question in her Ph.D. thesis. Her pioneering work also made it possible to read a star's surface temperature.

Bessel discovered Sirius' unseen companion star long before technology allowed us to see Sirius B and even longer before quantum mechanics explained the nature of white dwarfs.

In the midst of a forest, all you can see is a wall of tree trunks. So why, then, don't we see a wall of starlight when we look up at the forest of stars in the night sky?

Hundreds of times each year, a rock survives the fiery trip from space and lands on Earth. Take a look at some of these "fallen stars" that have been recovered from around the globe.

Most space rocks don’t pass anywhere near Earth. Meet the astronomers on wary watch for the ones that do. You’ll see firsthand how they are able to find asteroids in a celestial crowd.

Today, we accept the notion that enormous rocks exist within our solar system and that some of them fall to Earth. A little over 200 years ago, though, this idea garnered skepticism and ridicule.