Rhea: Saturns Second Largest Moon
5.12.1999

Rhea is the second largest moon of Saturn, behind Titan, and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea's rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn.

Star Trails in Southern Skies
15.07.2000

As the Earth spins on its axis, the stars seem to rotate around us. This motion produces the beautiful concentric arcs traced out by the stars in this time exposure of the southern hemisphere night sky. In the foreground is the dome of the Anglo-Australian Telescope in central New South Wales, Australia.

Rhea: Saturn's Second Largest Moon
8.06.2003

Rhea is the second largest moon of Saturn, behind Titan, and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea's rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn.

Rhea: Saturn's Second Largest Moon
14.10.1995

Rhea is the second largest moon of Saturn, behind Titan, and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea's rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn.

Mercury from Passing BepiColombo
28.06.2022

Which part of the Moon is this? No part -- because this is the planet Mercury. Mercury's old surface is heavily cratered like that of Earth's Moon. Mercury, while only slightly larger than Luna, is much denser and more massive than any Solar System moon because it is made mostly of iron.

Saturns Moon Rhea from Cassini
15.02.2005

Each moon of Saturn seems to come with its own mystery. Rhea, Saturn's second largest moon behind Titan, shows unusual wisps, visible above as light colored streaks. Higher resolution images of the wisps show them to be made of long braided fractures.

The Sun Unleashed: Monster Filament in Ultraviolet
9.04.2018

One of the most spectacular solar sights is an explosive flare. In 2011 June, the Sun unleashed somewhat impressive, medium-sized solar flare as rotation carried active regions of sunpots toward the solar limb. That...

In Motion: Uranus and Moons
30.11.2021

What's that moving across the sky? A planet just a bit too faint to see with the unaided eye: Uranus. The gas giant out past Saturn was tracked earlier this month near opposition -- when it was closest to Earth and at its brightest.

The Far Side of the Moon
25.02.2007

Does this moon look familiar? Possibly not, even though it is Earth's Moon. Locked in synchronous rotation, the Moon always presents its well-known near side to Earth. But from lunar orbit, Apollo astronauts also grew to know the Moon's far side.

APOD: 2023 January 11 Б Spiral Aurora over Iceland
11.01.2023

The scene may look like a fantasy, but it's really Iceland. The rock arch is named Gatklettur and located on the island's northwest coast. Some of the larger rocks in the foreground span a meter across. The fog over the rocks is really moving waves averaged over long exposures.