A Filament Across the Sun
20.08.2012

Is that a cloud hovering over the Sun? Yes, but it is quite different than a cloud hovering over the Earth. The long light feature on the left of the above color-inverted image is actually a solar filament and is composed of mostly charged hydrogen gas held aloft by the Sun's looping magnetic field.

Wringing a Wet Towel in Orbit
24.04.2013

What happens if you wring out a wet towel while floating in space? The water shouldn't fall toward the floor because while orbiting the Earth, free falling objects will appear to float. But will the water fly out from the towel, or what? The answer may surprise you.

Flowing Auroras Over Norway
9.06.2013

Have you ever seen an aurora? Auroras are occurring again with increasing frequency. With the Sun peaking at its eleven year maximum in aurora-triggering activity, it is exhibiting a greater abundance of sunspots, flares, and coronal mass ejections.

A Mercury Transit Sequence
3.05.2016

This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006. Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun.

Winter Hexagon over Manla Reservoir
22.01.2017

If you can find Orion, you might be able to find the Winter Hexagon. The Winter Hexagon involves some of the brightest stars visible, together forming a large and easily found pattern in the winter sky of Earth's northern hemisphere.

Blue Comet Meets Blue Stars
11.02.2018

What's that heading for the Pleiades star cluster? It appears to be Comet C/2016 R2 (PanSTARRS), but here, appearances are deceiving. On the right and far in the background, the famous Pleiades star cluster is dominated by blue light from massive young stars.

LDN 1471: A Windblown Star Cavity
5.05.2020

What is the cause of this unusual parabolic structure? This illuminated cavity, known as LDN 1471, was created by a newly forming star, seen as the bright source at the peak of the parabola.

APOD: 2024 June 25 Б The Dark Doodad Nebula
24.06.2024

What is that strange brown ribbon on the sky? When observing the star cluster NGC 4372, observers frequently take note of an unusual dark streak nearby running about three degrees in length. The streak, actually a long molecular cloud, has become known as the Dark Doodad Nebula.

APOD: 2024 August 11 Б Animation: Perseid Meteor Shower
10.08.2024

Where do Perseid meteors come from? Mostly small bits of stony grit, Perseid meteoroids were once expelled from Comet Swift-Tuttle and continue to follow this comet's orbit as they slowly disperse. The featured animation depicts the entire meteoroid stream as it orbits our Sun.

NGC 1850: Gas Clouds and Star Clusters
29.03.1999

There's nothing like it in our own Galaxy. Globular clusters as young as NGC 1850 don't exist here. Globular clusters only 40 millions of years old can still be found in the neighboring LMC galaxy, though, but perhaps none so unusual as NGC 1850.