Saturn: Shadows of a Seasonal Sundial
12.10.2011

Saturn's rings form one of the larger sundials known. This sundial, however, determines only the season of Saturn, not the time of day. In 2009, during Saturn's last equinox, Saturn's thin rings threw almost no shadows onto Saturn, since the ring plane pointed directly toward the Sun.

Sigmoids Predict Solar Eruptions
16.03.1999

On the Sun, S marks the spot. Solar explosions have been discovered to explode preferentially from regions marked with this letter. The surface of the quiet Sun is a maze of hot gas and flowing magnetic fields. When two regions of high magnetic field strength approach each other, they typically pass uneventfully.

Southwest Mercury
13.02.2000

The planet Mercury resembles a moon. Mercury's old surface is heavily cratered like many moons. Mercury is larger than most moons but smaller than Jupiter's moon Ganymede and Saturn's moon Titan. Mercury is much denser and more massive than any moon, though, because it is made mostly of iron.

A Zodiacal Sky over Horseshoe Bend
22.05.2017

What's causing the unusual ray of white light extending upward from the central horizon? Dust orbiting the Sun. At certain times of the year, a band of sun-reflecting dust from the inner Solar System rises prominently before sunrise and is called zodiacal light.

APOD: 2024 December 3 Б Ice Clouds over a Red Planet
3.12.2024

If you could stand on Mars -- what might you see? You might look out over a vast orange landscape covered with rocks under a dusty orange sky, with a blue-tinted Sun setting over the horizon, and odd-shaped water clouds hovering high overhead.

APOD: 2025 December 28 Б NGC 1898: Globular Cluster in the Large Magellanic Cloud
28.12.2025

Jewels don't shine this bright -- only stars do. And almost every spot in this jewel-box of an image from the Hubble Space Telescope is a star. Now, some stars are more red than our Sun, and some more blue -- but all of them are much farther away.

Palm Tree Partial Eclipse
13.04.2024

Only those along the narrow track of the Moon's shadow on April 8 saw a total solar eclipse. But most of North America still saw a partial eclipse of the Sun. From Clearwater, Florida, USA this single snapshot captured multiple images of that more widely viewed celestial event without observing the Sun directly.

Moonset from Taiwan
14.08.2013

It took three worlds to create this simple image. The first world was the Earth, which was quite prominent. The dividing line running horizontally below the middle separates sea from sky. On this part of the Earth, it was almost nighttime. The second world was the Moon, which was almost invisible.

The Gegenschein Over Chile
14.01.2014

Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles.

A Solar Prominence from SOHO
30.01.2022

How can gas float above the Sun? Twisted magnetic fields arching from the solar surface can trap ionized gas, suspending it in huge looping structures. These majestic plasma arches are seen as prominences above the solar limb.