Rainbow Airglow over the Azores
18.04.2021

Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere.

Hale-Bopp: The Great Comet of 1997
8.04.2022

Only twenty-five years ago, Comet Hale-Bopp rounded the Sun and offered a dazzling spectacle in planet Earth's night skies. Digitized from the original astrophoto on 35mm color slide film, this classic image of the Great Comet of 1997 was recorded a few days after its perihelion passage on April 1, 1997.

Messiers and Mars
15.06.2001

A telescopic tour of the constellation Sagittarius offers the many bright clusters and nebulae of dimensioned space in a starscape surrounding the galactic center. This gorgeous color deep-sky photograph visits two such lovely sights, cataloged by the 18th century cosmic tourist Charles Messier as M8 and M20.

Comet Lulin Approaches
2.02.2009

How bright will Comet Lulin become? No one knows for sure. Although it is notoriously difficult to accurately predict the brightness of newly discovered comets, Comet Lulin could well become visible to the unaided eye later this month.

Radio, The Big Ear, and the WOW Signal
2.05.2020

Since the early days of radio and television we have been freely broadcasting signals into space. For some time now, we have been listening too. A large radio telescope at Ohio State University known as affectionately The Big Ear was one of the first listeners.

Pleiades from Planet Earth
1.11.2025

The lovely Pleiades star cluster shines in Earth's night sky, a compact group of stars some 400 light-years distant toward the constellation Taurus and the Orion Arm of our Milky Way galaxy. Recognized since ancient times, the remarkable celestial gathering is visible to the unaided eye.

Unicorn, Fox Fur and Christmas Tree
25.12.2025

A star forming region cataloged as NGC 2264, this beautiful but complex arrangement of interstellar gas and dust is about 2,700 light-years distant in the faint but fanciful constellation Monoceros, the Unicorn. Seen...

Bright Planetary Nebula NGC 7027 from Hubble
9.01.2018

It is one of the brightest planetary nebulae on the sky -- what should it be named? First discovered in 1878, nebula NGC 7027 can be seen toward the constellation of the Swan (Cygnus) with a standard backyard telescope.

APOD: 2026 June 28 Б AR 4478: Giant Sunspot Group
28.06.2026

Right now, one of the largest sunspot groups in recent history is crossing the Sun. Active Region 4478 is not only big -- it's violent, showing tangled magnetic fields capable of throwing off huge clouds of particles into the Solar System. Some of these CMEs might impact the Earth.

Rainbow Airglow over the Azores
22.03.2016

Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere.