Why does an evergreen tree have a pyramid shape?

Those who admire the pyramid shape of an evergreen tree might enjoy knowing that its shape has evolved in response to wind, snow, and light.

Jan Oort: Celebrating his birthday and life

Dutch astronomer Jan Oort was born on April 28, 1900. He visualized a vast reservoir of icy comets on the fringes of our solar system, which now bears his name.

Moon near Antares and Saturn May 11-13

If they’re not up before your bedtime, watch this celestial threesome – the moon, Antares and Saturn – in the west before morning dawn.

Moon and Mercury after sunset August 4

It won't be easy to catch Mercury near the August 4 young moon. But if your sky is clear all the way to the western horizon after sunset, try it!

Do no harm to life on Mars? Ethical limits of Prime Directive

A philosopher argues that now is the time to figure it out, before we make the inevitable discovery of extraterrestrial life.

Old under-ice volcanoes on Mars

An oddly textured region of southern Mars is not ice-covered today. Yet landforms here - and now certain minerals - are associated with under-ice volcanoes.

Kepler confirms 1,284 new planets

The announcement more than doubles Kepler's confirmed exoplanets and suggests that, somewhere out there, we'll discover another Earth.

Why Planet 9 shouldn’t exist

Earlier this year, scientists presented evidence for a Planet Nine in the far outer solar system. Scientists think it exists, but - if so - how did it get there?

A pure methane sea on Titan

We knew that Saturn's moon Titan had seas and lakes of liquid hydrocarbons, but their exact composition was unknown until recently.

Just 40 light-years away, 3 potentially habitable planets

Earth-like planets aren't exclusively orbiting sunlike stars. Ultracool dwarf star TRAPPIST-1 hosts 3 potentially habitable planets.