Edwin Hubble Discovers the Universe
26.04.2020

How big is our universe? This very question, among others, was debated by two leading astronomers 100 years ago today in what has become known as astronomy's Great Debate. Many astronomers then believed that our Milky Way Galaxy was the entire universe. Many others, though, believed that our galaxy was just one of many.

The Hubble Deep Field
1.09.2002

Galaxies like colorful pieces of candy fill the Hubble Deep Field - one of humanity's most distant optical views of the Universe. The dimmest, some as faint as 30th magnitude (about four billion times...

The Hooker Telescope on Mt. Wilson
1.07.1995

In the 1920s, pictures from the Hooker Telescope on Mt. Wilson fundamentally changed our understanding of the cosmos. Astronomer Edwin Hubble, using photographs he took with this telescope, demonstrated that the objects his contemporaries called "spiral nebulae" were actually huge systems of stars - spiral galaxies, similar to our own Milky Way galaxy but incredibly distant.

APOD: 2025 October 26 Б Halloween and the Ghost Head Nebula
26.10.2025

Halloween's origin is ancient and astronomical. Since the fifth century BC, Halloween has been celebrated as a cross-quarter day, a day halfway between an equinox (equal day / equal night) and a solstice (minimum day / maximum night in the northern hemisphere).

ESO 184 G82: and the Supernova Gamma Ray Burst Connection
28.02.2002

Modern astronomers keep a long list of things that go bump in the night. Near the top are supernovae - the death explosions of massive stars, and gamma-ray bursts - the most powerful explosions seen across the Universe.

Two Black Holes Dancing in 3C 75
28.09.2014

What's happening at the center of active galaxy 3C 75? The two bright sources at the center of this composite x-ray (blue)/ radio (pink) image are co-orbiting supermassive black holes powering the giant radio source 3C 75.

Southwest Andromeda
17.09.2001

This new image composite of the southwest region of M31 from the Subaru Telescope shows many stars, nebulae, and star clusters never before resolved. An older population of stars near Andromeda's center causes the yellow hue visible on the upper right. Young blue stars stand out in the spiral arms on the lower left.

Big Dipper, Deep Sky
23.01.2016

The Big Dipper is an easy to recognize, well-known asterism in northern skies, though many see the Plough or Wagon. Famous bright nebulae of the north can also be found along its familiar lines, highlighted in this carefully composed scene with telescopic insets framed in the wider-field skyview.

Magellanic Clouds over Chile
11.02.2023

The two prominent clouds in this Chilean Atacama Desert skyscape captured on January 21 actually lie beyond our Milky Way galaxy. Known as the Large and the Small Magellanic Clouds they are so named for the 16th century Portuguese explorer Ferdinand Magellan, leader of the first circumnavigation of planet Earth.

Andromeda Island Universe
8.09.2000

How far can you see? The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda