NGC 4911: Spiral Diving into a Dense Cluster
8.09.2010

Why are there faint rings around this spiral galaxy? Possibly because the galaxy, NGC 4911, is being pulled at by its neighbors as it falls into the enormous Coma Cluster of Galaxies.

J102815: A Star That Should Not Exist
7.09.2011

Why does this star have so few heavy elements? Stars born in the generation of our Sun have an expected abundance of elements heavier than hydrogen and helium mixed into their atmospheres. Stars born...

Dancing Ghosts: Curved Jets from Active Galaxies
1.09.2021

Why would galaxies emit jets that look like ghosts? And furthermore, why do they appear to be dancing? The curled and fluffy jets from the supermassive black holes at the centers of two host galaxies (top center and lower left) are unlike anything seen before.

Galaxy Cluster Abell 1689 Deflects Light
17.09.2013

It is one of the most massive objects in the visible universe. In this view from the Hubble Space Telescope's Advanced Camera for Surveys, Abell 1689 is seen to warp space as predicted by Einstein's theory of gravity -- deflecting light from individual galaxies which lie behind the cluster to produce multiple, curved images.

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.

Analemma over the Callanish Stones
18.09.2022

If you went outside at the same time every day and took a picture that included the Sun, how would the Sun's position change? A more visual answer to that question is an analemma, a composite image taken from the same spot at the same time over the course of a year.

APOD: 2023 April 11 Б North Star: Polaris and Surrounding Dust
11.04.2023

Why is Polaris called the North Star? First, Polaris is the nearest bright star toward the north spin axis of the Earth. Therefore, as the Earth turns, stars appear to revolve around Polaris, but Polaris itself always stays in the same northerly direction -- making it the North Star.

A Protected Night Sky Over Flagstaff
16.04.2008

This sky is protected. Yesterday marked the 50 year anniversary of the first lighting ordinance ever enacted, which restricted searchlight advertisements from sweeping the night skies above Flagstaff, Arizona, USA. Flagstaff now enjoys...

Gamma-Ray Burster
19.03.1997

What and where are the Gamma-Ray Bursters? Since their discovery in the early 1970s, nobody has been able to explain the cause of mysterious flashes of gamma rays that come from seemingly random directions on the sky.

SIRTF Streak
5.09.2003

Streaking skyward, a Boeing Delta 2-Heavy rocket carries NASA's Space InfraRed Telescope Facility (SIRTF) aloft during the early morning hours of August 25th. The dramatic scene was recorded in a time exposure from...