Discovery Spring
20.03.2001

Welcome to the equinox! Moving northward in Earth's sky, today the Sun crosses the celestial equator at 13:31 Universal Time bringing Spring to the north and Fall to the south. The change...

Outbound from Mercury
16.07.2002

After just passing Mercury, the robot spacecraft Mariner 10 looked back. The above picture is what it saw. Mercury, the closest planet to the Sun, is heavily cratered much like Earth's Moon.

Anticrepuscular Rays over Florida
18.03.2020

What's happening behind those clouds? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a Sun setting on the other side of the sky. Pictured here are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds.

APOD: 2024 March 4 Б Light Pillars Over Inner Mongolia
4.03.2024

What's happening across that field? Pictured here are not auroras but nearby light pillars, a phenomenon typically much closer. In most places on Earth, a lucky viewer can see a Sun pillar, a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting sunlight from the upper atmosphere.

APOD: 2026 March 23 Б Light Pillars and Orion over Mohe
23.03.2026

What's happening at the end of that street? Pictured here are not auroras but light pillars, a phenomenon typically much closer. In most places on Earth, a lucky viewer...

The Local Fluff
29.08.2010

The stars are not alone. In the disk of our Milky Way Galaxy about 10 percent of visible matter is in the form of gas, called the interstellar medium (ISM). The ISM is not uniform, and shows patchiness even near our Sun.

Mercury Spotting
27.05.2012

Can you spot the planet? The diminutive disk of Mercury, the solar system's innermost planet, spent about five hours crossing in front of the enormous solar disk in 2003, as viewed from the general vicinity of planet Earth.

Anticrepuscular Rays Over Colorado
28.11.2010

What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Pictured above are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds.

Ultraviolet Earth from an Observatory on the Moon
28.10.2018

Which planet is this? Earth. The featured false color picture shows how the Earth shines in ultraviolet (UV) light. The image is historic because it was taken from the surface of the Moon by humanity's only lunar observatory.

Manhattanhenge: A New York City Sunset
6.07.2014

This coming Saturday, if it is clear, well placed New Yorkers can go outside at sunset and watch their city act like a modern version of Stonehenge. Manhattan's streets will flood dramatically with sunlight just as the Sun sets precisely at each street's western end.