A Quadruple Lunar Halo Over Spain
3.12.2012

Sometimes falling ice crystals make the atmosphere into a giant lens causing arcs and halos to appear around the Sun or Moon. This past Saturday night was just such a time near Madrid, Spain, where a winter sky displayed not only a bright Moon but as many as four rare lunar halos.

Periodic Comet Swift-Tuttle
18.02.1996

Comet Swift-Tuttle, shown above in false color, is the largest object known to make repeated passes near the Earth. It is also one of the oldest known periodic comets with sightings spanning two millennia.

Exceptional Rocket Waves Destroy Sun Dog
22.02.2010

What created those rocket waves, and why did they destroy that sun dog? Close inspection of the above image shows not only a rocket rising near the center, but unusual air ripples around it and a colorful sundog to the far right.

Saturns Iapetus: Painted Moon
9.08.2009

What has happened to Saturn's moon Iapetus? Vast sections of this strange world are dark as coal, while others are as bright as ice. The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon.

Abell 370: Galaxy Cluster Gravitational Lens
21.09.2009

What is that strange arc? While imaging the cluster of galaxies Abell 370, astronomers had noted an unusual arc to the right of many cluster galaxies. Although curious, one initial response was to avoid commenting on the arc because nothing like it had ever been noted before.

APOD: 2020 July 22 Б The Structured Tails of Comet NEOWISE
21.07.2020

What is creating the structure in Comet NEOWISE's tails? Of the two tails evident, the blue ion tail on the left points directly away from the Sun and is pushed out by the flowing and charged solar wind.

Kepler's Supernova Remnant in X Rays
15.05.2013

What caused this mess? Some type of star exploded to create the unusually shaped nebula known as Kepler's supernova remnant, but which type? Light from the stellar explosion that created this energized cosmic cloud was first seen on planet Earth in October 1604, a mere four hundred years ago.

The Dark River to Antares
15.05.2020

A dark river seems to flow through this sky from the horizon toward colorful clouds near red giant star Antares. Murky looking, the dark river is a dusty nebula obscuring background starlight near the central Milky Way, although the dark dust nebula contains mostly hydrogen molecular gas.

Dark Matter Ring Modeled around Galaxy Cluster CL0024 17
16.05.2007

How do we know that dark matter isn't just normal matter exhibiting strange gravity? A new observation of gravitationally magnified faint galaxies far in the distance behind a massive cluster of galaxies is shedding new dark on the subject.

Saturns Iapetus: Painted Moon
13.01.2012

What has happened to Saturn's moon Iapetus? Vast sections of this strange world are dark as coal, while others are as bright as ice. The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon.