Perihelion and Aphelion
3.07.2009

This year Aphelion, the point in Earth's elliptical orbit when it is farthest from the Sun, occurs tomorrow, July 4th. Of course, that doesn't affect the seasons on our fair planet. Those...

Supernova 1994D and the Unexpected Universe
30.12.1998

Far away, long ago, a star exploded. Supernova 1994D, visible as the bright spot on the lower left, occurred in the outskirts of disk galaxy NGC 4526. Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae.

APOD: 2025 January 1 Б Alpha Centauri: The Closest Star System
1.01.2025

The closest star system to the Sun is the Alpha Centauri system. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star. The bright stars Alpha Centauri...

Io: Moon Over Jupiter
20.04.2001

How big is the Jovian moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite.

Milky Way Over Quiver Tree Forest
15.05.2016

In front of a famous background of stars and galaxies lies some of Earth's more unusual trees. Known as quiver trees, they are actually succulent aloe plants that can grow to tree-like proportions. The quiver tree name is derived from the historical usefulness of their hollowed branches as dart holders.

Apogee Full Moon
18.01.2014

This big, bright, beautiful Full Moon rose over Lick Observatory Wednesday night. Traditionally a full moon in January might be called the Wolf Moon. But this moon reached its full phase on January 16, 4:54 UT, within about 2 hours of apogee, the most distant point in its elliptical orbit around planet Earth.

APOD: 2025 April 7 Б NGC 4414: A Flocculent Spiral Galaxy
7.04.2025

How much mass do flocculent spirals hide? The featured image of flocculent spiral galaxy NGC 4414 was taken with the Hubble Space Telescope to help answer this question. Flocculent spirals -- galaxies without well-defined spiral arms -- are a quite common form of galaxy, and NGC 4414 is one of the closest.

Anemic Spiral NGC 4921 from Hubble
15.05.2019

How far away is spiral galaxy NGC 4921? It's surpringly important to know. Although presently estimated to be about 300 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe.

APOD: 2025 November 25 Б Comet Lemmon and the Milky Way
25.11.2025

What did Comet Lemmon look like when it was at its best? One example is pictured here, featuring three celestial spectacles all at different distances. The closest spectacle is the snowcapped Meili Mountains, part of the Himalayas in China.

Milky Way and Aurora over Antarctica
27.07.2015

It has been one of the better skies of this long night. In parts of Antarctica, not only is it winter, but the Sun can spend weeks below the horizon. At China's Zhongshan Station, people sometimes venture out into the cold to photograph a spectacular night sky.