APOD@coRank: Featured

The Matter of the Bullet Cluster

APOD — Thu, 28 Aug 2008 01:57:13 GMT

The matter in galaxy cluster 1E 0657-56, fondly known as the "bullet cluster", is shown in this composite image . A mere 3.4 billion light-years away, the bullet cluster's individual galaxies are seen in the optical image data, but their total mass adds up to far less than the mass of the cluster's two clouds of hot x-ray emitting gas shown in red. Representing even more mass than the optical galaxies and x-ray gas combined, the blue hues show the distribution of dark matter in the cluster . Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. In a text book example of a shock front, the bullet-shaped cloud of gas at the right was distorted during the titanic collision between two galaxy clusters that created the larger bullet cluster itself. But the dark matter present has not interacted with the cluster gas except by gravity. The clear separation of dark matter and gas clouds is considered direct evidence that dark matter exists .

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August Moons

APOD — Thu, 28 Aug 2008 01:57:13 GMT

This August was eclipse season . The month's first New Moon and Full Moon were both seen in darkened skies during a solar and lunar eclipse. Blocking the Sun, the left panel's New Moon was captured during the total solar eclipse of August 1 from the path of totality overlooking Novosibirsk (Siberia) Reservoir, locally known as the Ob Sea. A lovely solar corona and bright inner planets Mercury and Venus emerged during the total eclipse phase, while the flickering view screens of eclipse watchers' digital cameras dotted the landscape. On the right, the Full Moon grazed Earth's shadow nearly 15 days later in a partial lunar eclipse. That serene view was recorded during an early evening stroll along the shores of the Odet River near the city of Quimper in western France. For planet Earth there are about two seasons each year during which the orientation of the Moon's orbit is favorable for solar and lunar eclipses. The next eclipse season begins in January 2009 with an annular solar eclipse .

Read more... | Original picture | Votes so far: 47 / 3

August Moons

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Read more... | Original picture | Votes so far: 47 / 3

Active Galaxy NGC 1275

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Active galaxy NGC 1275 is the central, dominant member of the large and relatively nearby Perseus Cluster of Galaxies . A prodigious source of x-rays and radio emission, NGC 1275 accretes matter as entire galaxies fall into it, ultimately feeding a supermassive black hole at the galaxy's core. This stunning visible light image from the Hubble Space Telescope shows galactic debris and filaments of glowing gas, some up to 20,000 light-years long. The filaments persist in NGC 1275, even though the turmoil of galactic collisions should destroy them. What keeps the filaments together? Recent work indicates that the structures, pushed out from the galaxy's center by the black hole's activity, are held together by magnetic fields. To add x-ray data from the Chandra Observatory and radio data from the Very Large Array to the Hubble image, just slide your cursor over the picture. In the resulting composite , x-rays highlight the shells of hot gas surrounding the center of the galaxy, with radio emission filling giant bubble-shaped cavities. Also known as Perseus A, NGC 1275 spans over 100,000 light years and lies about 230 million light years away.

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NGC 6960: The Witch's Broom Nebula

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Ten thousand years ago, before the dawn of recorded human history, a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star and record the colorful expanding cloud as the Veil Nebula. Pictured above is the west end of the Veil Nebula known technically as NGC 6960 but less formally as the Witch's Broom Nebula. The expanding debris cloud gains its colors by sweeping up and exciting existing nearby gas. The supernova remnant lies about 1400 light-years away towards the constellation of Cygnus. This Witch's Broom actually spans over three times the angular size of the full Moon. The bright star 52 Cygnus is visible with the unaided eye from a dark location but unrelated to the ancient supernova.

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Earth's Shadow

APOD — Thu, 28 Aug 2008 01:57:13 GMT

The dark, inner shadow of planet Earth is called the umbra. Shaped like a cone extending into space, the umbra has a circular cross section that can be most easily seen during a lunar eclipse. For example, last Saturday the Full Moon slid across the northern edge of the umbra. Entertaining moon watchers throughout Earth's eastern hemisphere, the lunar passage created a deep but partial lunar eclipse. This composite image uses successive pictures recorded during the eclipse from Athens, Greece to trace out a large part of the umbra's curved edge. The result nicely illustrates the relative size of the umbra's cross section at the distance of the Moon, as well as the Moon's path through the Earth's shadow.

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NGC 6960: The Witch's Broom Nebula

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Read more... | Original picture | Votes so far: 53 / 3

Baily's Beads near Solar Eclipse Totality

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Just before the Sun blacks out, something strange occurs. As the Moon moves to completely cover the Sun in a total solar eclipse, beads of bright sunlight stream around the edge of the Moon. This effect, known as Baily's beads, is named after Francis Baily who called attention to the phenomenon in 1836. Although, the number and brightness of Baily's beads used to be unpredictable, today the Moon is so well mapped that general features regarding Baily's beads are expected. When a single bead dominates, it is called the diamond ring effect, and is typically seen just before totality. Pictured above, a series of images recorded Baily's beads at times surrounding the recent total solar eclipse visible from Novosibirsk, Russia. The complete series can be seen by scrolling right. At the end of totality, as the Sun again emerges from behind the moon, Baily's beads may again be visible -- but now on the other side of the Moon.

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Baily's Beads near Solar Eclipse Totality

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Read more... | Original picture | Votes so far: 52 / 3

Io's Surface: Under Construction

APOD — Thu, 28 Aug 2008 01:57:13 GMT

Like the downtown area of your favorite city, the roads you drive to work on, and any self-respecting web site ... Io's surface is constantly under construction. This moon of Jupiter holds the distinction of being the Solar System's most volcanically active body -- its bizarre looking surface continuously formed and reformed by lava flows. Generated using 1996 data from NASA's Galileo spacecraft, this high resolution composite image is centered on the side of Io that always faces away from Jupiter. It has been enhanced to emphasize Io's surface brightness and color variations, revealing features as small as 1.5 miles across. The notable absence of impact craters suggests that the entire surface is covered with new volcanic deposits much more rapidly than craters are created. What drives this volcanic powerhouse? A likely energy source is the changing gravitational tides caused by Jupiter and the other Galilean moons as Io orbits the massive gas giant planet. Heating Io's interior, the pumping tides would generate the sulfurous volcanic activity.

Read more... | Original picture | Votes so far: 52 / 4