Astronomy Picture Of the Day (APOD)The Millennium that Defines Universe
Welcome to millennium three. During millennium two, humanity continually redefined its concept of "Universe": first as spheres centered on the Earth, in mid-millennium as the Solar System, a few centuries ago as the Galaxy, and within the last century as the matter emanating from the Big Bang.
The Millennium that Defined Earth
When the second millennium began, people generally knew that the Earth was round, but few saw much of it beyond their local village. As the millennium progressed, humans mapped the continents, circumnavigated the globe, and determined the composition of the Earth.
A Year of Resolving Backgrounds
No matter which direction you look, no matter what type of light you see, the sky glows - but why? The sources of many of these background radiations have remained long-standing puzzles, but this millennial year brought some partial resolutions.
The Dark Horsehead Nebula
While drifting through the cosmos, sculpted by stellar winds and radiation, this magnificent interstellar dust cloud has chanced to assume a recognizable shape. Fittingly named The Horsehead Nebula it is embedded in the immense complex of star forming gas and dust surrounding the Orion Nebula some 1,500 light-years distant.
Moon Mare and Montes
This arresting image of the third quarter moon in the excellent skies above the Pine Crest Farm Observatory, Dell Prairie, Wisconsin, was recorded with a 24 inch telescope and digital camera on October 19.
The Dust and Ion Tails of Comet Hale Bopp
In 1977, Comet Hale-Bopp's intrinsic brightness exceeded any comet since 1811. Since it peaked on the other side of the Earth's orbit, however, the comet appeared only brighter than any comet in two decades. Visible above are the two tails shed by Comet Hale-Bopp.
Jupiter, Io, and Shadow
Just as planets orbit our Sun, Jupiter's Moons orbit Jupiter. Pictured above is the closest of Jupiter's Galilean Satellites, Io, superposed in front of the giant planet it circles. To the left of Io is a dark spot that is its own shadow.
The Eclipse Tree
If you look closely at the shadow of this tree, you will see something quite unusual: it is composed of hundreds of images of a partially eclipsed Sun. Early today, trees across North America will be casting similar shadows as a partial eclipse of the Sun takes place.
NGC 1850: Gas Clouds and Star Clusters
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.
Summer at the South Pole
The December solstice brings the beginning of Winter to Earth's Northern Hemisphere and Summer time to the South! This view of Earth's Southern Hemisphere near the beginning of Summer was created using images from the Galileo spacecraft taken during its December 1990 flyby of our fair planet.