The Gegenschein Over Chile
14.01.2014

Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles.

Rumors of a Strange Universe
27.02.2004

Only a few short years ago, when the APOD editors were in graduate school, the pervasive, cosmic Dark Energy was not even seriously discussed. Of course, it now appears that this strange energy dominates the cosmos (as well as lectures on cosmology) and provides a repulsive force accelerating the large scale expansion of the Universe.

The Milky Way Over Mauna Kea
27.01.2009

Have you ever seen the band of our Milky Way Galaxy? In a clear sky from a dark location at the right time, a faint band of light becomes visible across the sky. Soon after your eyes become dark adapted, you might spot the band for the first time. It may then become obvious.

A Dust Devil on Mars
3.09.2002

Does the surface of Mars change? When inspecting yearly images of the Martian surface taken by the robot spacecraft Mars Global Surveyor currently orbiting Mars, sometimes new dark trails are visible. Although originally...

Galaxy Cluster A2199
22.01.1997

It's bigger than a bread box. In fact, it's much bigger than all bread boxes put together. Abell 2199 is huge. In fact, it is a close, large cluster of galaxies, containing several thousands of galaxies centered around a central dominant galaxy.

The Sagittarius Dwarf Tidal Stream
30.09.2003

Is our Milky Way Galaxy out to lunch? Recent wide field images and analyses now indicate that our home galaxy is actually still in the process of devouring its closest satellite neighbor. This unfortunate...

Penumbral Eclipse Rising
18.02.2017

As seen from Cocoa Beach Pier, Florida, planet Earth, the Moon rose at sunset on February 10 while gliding through Earth's faint outer shadow. In progress was the first eclipse of 2017, a penumbral lunar eclipse followed in this digital stack of seaside exposures.

Milky Way Falls
12.01.2019

It can be the driest place on planet Earth, but water still flows in Chile's Atacama desert, high in the mountains. After discovering this small creek with running water, the photographer returned...

The Hydra Cluster of Galaxies
16.04.2001

The Hydra Cluster of Galaxies contains well over 100 bright galaxies - but perhaps fewer galaxies than might be expected from its mass. Clusters of galaxies are the largest gravitationally bound objects in the universe.

The Sagittarius Dwarf Tidal Stream
29.05.2005

Is our Milky Way Galaxy out to lunch? Recent wide field images and analyses now indicate that our home galaxy is actually still in the process of devouring one of its closer satellite neighbors.