Astronomy Picture Of the Day (APOD)Andromeda Island Universe
The most distant object easily visible to the eye is M31, the great Andromeda Galaxy some two and a half million light-years away. But without a telescope, even this immense spiral galaxy - spanning over 200,000 light years - appears as a faint, nebulous cloud in the constellation Andromeda.
The Mystery of the Fading Star
Every 27 years Epsilon Aurigae fades, remaining dim for roughly two years before growing bright again. Since the 19th century, astronomers have studied the mystery star, eventually arguing that Epsilon Aur, centered in this telescopic skyview, was actually undergoing a long eclipse by a dark companion object.
The Tail of the Small Magellanic Cloud
A satellite galaxy of our Milky Way, the Small Magellanic Cloud is wonder of the southern sky, named for 16th century Portuguese circumnavigator Ferdinand Magellan. Some 200,000 light-years distant in the constellation Tucana...
The Spotty Surface of Betelgeuse
Betelgeuse really is a big star. If placed at the center of our Solar System it would extend to the orbit of Jupiter. But like all stars except the Sun, Betelgeuse is so distant it usually appears as a single point of light, even in large telescopes.
A Roll Cloud Over Uruguay
What kind of cloud is this? A roll cloud. These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form a cloud.
Comet Halleys Nucleus: An Orbiting Iceberg
What does a comet nucleus look like? Formed from the primordial stuff of the Solar System, comet nuclei were thought to resemble very dirty icebergs. But ground-based telescopes revealed only the surrounding cloud of gas and dust of active comets nearing the Sun, clearly resolving only the comet's coma, and the characteristic cometary tails.
A Force from Empty Space: The Casimir Effect
This tiny ball provides evidence that the universe will expand forever. Measuring slightly over one tenth of a millimeter, the ball moves toward a smooth plate in response to energy fluctuations in the vacuum of empty space.
Blue Moon Eclipse
The International Year of Astronomy 2009 ended with a Blue Moon and a partial lunar eclipse, as the second Full Moon of December grazed the Earth's shadow on December 31st. The New Year...
Not a Blue Moon
This bright Full Moon was captured on December 2nd, shining above a church overlooking the River Po, in Turin, Italy, It was the first Full Moon in December. Shining on celebrations of New Year...
Dust and the Helix Nebula
Dust makes this cosmic eye look red. The eerie Spitzer Space Telescope image shows infrared radiation from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation Aquarius.