Astronomy Picture of the Day
APOD: 2011 October 27 - Young Suns of NGC 7129
Explanation: Young suns still lie within dusty NGC 7129, some 3,000 light-years away toward the royal constellation Cepheus. While these stars are at a relatively tender age, only a few million years old, it is likely that our own Sun formed in a similar stellar nursery some five billion years ago. Most noticeable in the sharp image are the lovely bluish dust clouds that reflect the youthful starlight. But the compact, deep red crescent shapes are also markers of energetic, young stellar objects. Known as Herbig-Haro objects, their shape and color is characteristic of glowing hydrogen gas shocked by jets streaming away from newborn stars. Paler, extended filaments of redish emission mingling with the bluish clouds are caused by dust grains effectively converting the invisible ultraviolet starlight to visible red light through photoluminesence. Ultimately the natal gas and dust in the region will be dispersed, the stars drifting apart as the loose cluster orbits the center of the Galaxy. At the estimated distance of NGC 7129, this telescopic view spans about 40 light-years.
APOD: 2009 March 7 - Comet Lulin and Distant Galaxies
Explanation: Now fading in our night sky, Comet Lulin has provided some lovely cosmic vistas. Moving rapidly against the background of stars, Lulin briefly posed with the likes of Saturn, and Regulus (Alpha Leo). But here it is seen against a field of distant galaxies. To reveal the faint background galaxies and trace the comet's fading tail, the remarkable picture is a blended composite of telescopic exposures aligned with the both the stars and the speedy comet. The largest galaxies seen left of the comet's head or coma are cataloged as NGC 3016, NGC 3019, NGC 3020 and NGC 3024 and lie at a distance of 100 million light-years or so. When the exposures were made, on February 28, the comet was about 3.6 light-minutes from Earth.
APOD: 2009 January 9 - NGC 4945 in Centaurus
Explanation: Large, dusty, spiral galaxy NGC 4945 is seen edge-on near the center of this rich telescopic image. The field of view spans nearly 2 degrees, or about 4 times the width of the Full Moon, toward the expansive southern constellation Centaurus. About 13 million light-years distant, NGC 4945 is almost the size of our own Milky Way Galaxy. But X-ray and infrared observations reveal even more high energy emission and star formation in the core of NGC 4945. The other prominent galaxy in the field, NGC 4976, is an elliptical galaxy. Left of center, NGC 4976 is much farther away, at a distance of about 35 million light-years, and not physically associated with NGC 4945.
APOD: 2008 December 4 - Venus in the Moon
Explanation: On December 1, bright planets Venus and Jupiter gathered near the young crescent Moon, an inspiring celestial scene in early evening skies around the world. But from some locations the Moon actually passed in front of Venus, interrupting the tight grouping with a lunar occultation. Captured from Wildon, Austria, this twilight view shows the silvery evening star about five minutes before it slipped behind the dark lunar limb and vanished from sight for more than hour. The image is a combination of long and short exposures showing details of the lunar surface illuminated by both faint earthshine and bright sunlight. In the inset, recorded later in darkened skies over Breil-sur-Roya in southeastern France, a dazzling Venus has reappeared below the bright lunar crescent. Of course, Jupiter, at the upper right about 2 degrees from Venus and Moon, is sporting moons of its own seen as tiny pinpricks of light on either side of the bright planet.
APOD: 2008 October 9 - Massive Stars in NGC 6357
Explanation: Massive stars lie within NGC 6357, an expansive emission nebula complex some 8,000 light-years away in the tail of the constellation Scorpius. In fact, positioned just below center in this close-up view of NGC 6357, star cluster Pismis 24 includes some of the most massive stars known in the galaxy, stars with over 100 times the mass of the Sun. The nebula's bright central region also contains dusty pillars of molecular gas, likely hiding massive protostars from the prying eyes of optical instruments. Intricate shapes in the nebula are carved by interstellar winds and energetic radiation from the young and newly forming massive stars. This alluring telescopic view spans just under 50 light-years at the estimated distance of NGC 6357.
APOD: 2008 July 19 - M16 and the Eagle Nebula
Explanation: Young star cluster M16 is surrounded by natal clouds of cosmic dust and glowing gas also known as The Eagle Nebula. This beautifully detailed image of the region includes fantastic shapes made famous in well-known Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the upper left edge of the nebula is another dusty starforming column known as the Fairy of Eagle Nebula. M16 and the Eagle Nebula lie about 7,000 light-years away, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).
APOD: 2008 April 3 - South of Orion
Explanation: This tantalizing array of nebulae and stars can be found about 2 degrees south of the famous star-forming Orion Nebula. The region abounds with energetic young stars producing jets and outflows that push through the surrounding material at speeds of hundreds of kilometers per second. The interaction creates luminous shock waves known as Herbig-Haro (HH) objects. For example, the graceful, flowing arc just right of center is cataloged as HH 222, also called the Waterfall Nebula. Seen below the Waterfall, HH 401 has a distinctive cone shape. The bright bluish nebula below and left of center is NGC 1999, a dusty cloud reflecting light from an embedded variable star. The entire cosmic vista spans over 30 light-years, near the edge of the Orion molecular cloud complex some 1,500 light-years distant.
APOD: 2008 March 29 - Spiral Galaxy NGC 2841
Explanation: Some 50 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk with tightly wound spiral arms. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way Galaxy. The galaxy's dust lanes and turbulent star-forming regions are found along the spiral arms, but X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841. Of course, the prominent stars with a spiky appearance in the picture are close foreground objects within the Milky Way and not associated with NGC 2841.
APOD: 2007 September 6 - Time Tunnel
Explanation: Spiky stars are nearby, but fuzzy galaxies are strewn far across the Universe in this cosmic view. Spanning about 1/2 degree on the sky, the pretty picture is the result of astronomer Johannes Schedler's project to look back in time, toward a quasar 12.7 billion light-years away. The quasar is just visible in the full resolution image at the position marked by short vertical lines (center). The intrinsically bright nucleus of a young, active galaxy powered by a supermassive black hole, the quasar was recently identified as one of the most distant objects known. Since light travels at a finite speed, the galaxies receding into the distance are seen as they were in the increasingly remote past. The quasar appears as it did about 12.7 billion years ago, when the Universe was just 7 percent of its present age. Of course, the expansion of the Universe has redshifted the light. Schedler added image data extending to the near-infrared, acquired by collaborator Ken Crawford, to detect the distant quasar, with a measured redshift of 6.04.
APOD: 2007 June 29 - Cat's Eye Wide and Deep
Explanation: The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of this impressive wide-angle view. But the composite image also combines many short and long exposures to reveal the nebula's extremely faint halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the right, some 50 million light-years beyond the Cat's Eye, lies spiral galaxy NGC 6552.
APOD: 2007 March 8 - Eclipsed Moon and Stars
Explanation: This dramatic image features a dark red Moon during a total lunar eclipse -- celestial shadow play enjoyed by many denizens of planet Earth last Saturday. Recorded near Wildon, Austria, the picture is a composite of two exposures; a relatively short exposure to feature the lunar surface and a longer exposure to capture background stars in the constellation Leo. Completely immersed in Earth's cone-shaped shadow during the total eclipse phase, the lunar surface is still illuminated by sunlight, reddened and refracted into the dark shadow region by a dusty atmosphere. As a result, familiar details of the Moon's nearside are easy to pick out, including the smooth lunar mare and the large ray crater Tycho. In this telescopic view, the background stars are faint and most would be invisible to the naked eye.
APOD: 2006 September 8 - Messier 110
Explanation: This very sharp telescopic vista features the last object in the modern version of Charles Messier's catalog of bright clusters and nebulae - Messier 110. A dwarf elliptical galaxy, M110 (aka NGC 205) is actually a bright satellite of the large spiral galaxy Andromeda, making M110 a fellow member of the local group of galaxies. Seen through a foreground of nearby stars, M110 is about 15,000 light-years across. That makes it comparable in size to satellite galaxies of our own Milky Way, the Large and Small Magellanic Clouds. Though elliptical galaxies are normally thought to be lacking in gas and dust to form new stars, M110 is known to contain young stars, and faint dust clouds can easily be seen in this detailed image at about the 7 and 11 o'clock positions relative to the galaxy center.
APOD: 2006 June 23 - East of Antares
Explanation: East of Antares, dark markings seem to sprawl through the crowded star fields toward the center of our Milky Way Galaxy. Cataloged in the early 20th century by astronomer E. E. Barnard, the obscuring interstellar dust clouds include B72, B77, B78, and B59, seen in silhouette against the starry background. Here, their combined shape suggests smoke rising from a pipe, and so the dark nebula's popular name is the Pipe Nebula. This gorgeous and expansive view was recorded in very dark skies over Hakos, Namibia. It covers a full 10 by 7 degree field in the pronounceable constellation Ophiuchus.
APOD: 2006 April 15 - Galaxy Wars: M81 versus M82
Explanation: In this stunning cosmic vista, galaxy M81 is on the left surrounded by blue spiral arms. On the right marked by massive gas and dust clouds, is M82. These two mammoth galaxies have been locked in gravitational combat for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. In a few billion years only one galaxy will remain.
APOD: 2006 February 16 - The Color of the Moon
Explanation: Earth's Moon is normally seen in subtle shades of grey or yellow. But small color differences have been greatly exaggerated to make this dramatic mosaic image of the Moon's gibbous phase. The familiar Sea of Tranquility (Mare Tranquillitatis) is the blue area right of center. White lines radiate from the crater Tycho at bottom left, while purplish tones mottle the crater Copernicus left of center. Though exaggerated, the different colors are recognized to correspond to real differences in the chemical makeup of the lunar surface - blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. Calibrated by rock samples from the Apollo missions, similar multicolor images from spacecraft have been used to explore the Moon's global surface composition.
APOD: 2005 June 7 - Galaxies in View
Explanation: Galaxies abound in this cosmic scene, a well chosen telescopic view toward the northern constellation of Ursa Major. Most noticeable are the striking pair of spiral galaxies - NGC 3718 (above, right) and NGC 3729 (below center) - a mere 52 million light-years distant. In particular, NGC 3718 has dramatic dust lanes sweeping through its bright central region and extensive but faint spiral arms. Seen about 150 thousand light-years apart, these two galaxies are likely interacting gravitationally, accounting for the warped and peculiar appearance of NGC 3718. While a careful study of the deep image reveals a number of fainter and more distant background galaxies, another remarkable galaxy grouping known as Hickson Group 56 can be found just to the right of NGC 3718. Hickson Group 56 contains five interacting galaxies and lies over 400 million light-years away.
APOD: 2005 May 12 - Stars, Galaxies, and Comet Tempel 1
Explanation: Faint comet Tempel 1 sports a fuzzy blue-tinted tail, just right of center in this lovely field of stars. Recorded on May 3rd slowly sweeping through the constellation Virgo, periodic comet Tempel 1 orbits the Sun once every 5.5 years. Also caught in the skyview are two galaxies at the upper left - NGC 4762 and NGC 4754 - both members of the large Virgo Cluster of galaxies. Classified as a lenticular galaxy, NGC 4762 presents an edge-on disk as a narrow gash of light while NGC 4754 is a football-shaped elliptical galaxy. Similar in apparent size, the galaxies and comet make for an intriguing visual comparison, but Tempel 1 is only about 3 light-minutes from planet Earth. The two Virgo cluster galaxies are 50 million light-years away. NASA's Deep Impact spacecraft is scheduled to encounter Tempel 1 on July 4th, launching a probe to impact the comet's nucleus.
APOD: 2004 April 8 - Elusive Jellyfish Nebula
Explanation: Normally faint and elusive, the Jellyfish Nebula is caught in the net of this spectacular wide-field telescopic view. Flanked by two yellow-tinted stars at the foot of a celestial twin - Mu and Eta Geminorum - the Jellyfish Nebula is the brighter arcing ridge of emission with dangling tentacles just right of center. Here, the cosmic jellyfish is seen to be part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from an exploded star some 5,000 light-years away. Also in view, emission nebula IC 444 nearly fills the field to the upper left, dotted with small blue reflection nebulae. Like its cousin in astrophysical waters, the Crab Nebula, IC 443 is known to harbor a neutron star, the collapsed core of the massive star that exploded over 30,000 years ago.
APOD: 2003 October 24 - Mars Moons
Explanation: This year's record close approach of Mars inspired many to enjoy telescopic views of the red planet. But while Mars was so bright it was hard to miss, spotting Mars' two diminutive moons was still a good test for observers with modest sized instruments. Mars' moons were discovered in August of 1877 by Asaph Hall at the US Naval Observatory using the large 26-inch Alvan Clark refractor. Recorded on this August 22nd, innermost moon Phobos and outermost moon Deimos are seen here against the planet's glare in a digital composite image. The picture consists of of a long exposure capturing the faint, city-sized moons and overexposing the planetary disk, combined with a well exposed image of the red planet, revealing dark markings on the surface and the white south polar cap. The images were taken by astronomer Johannes Schedler using an 11-inch Schmidt-Cassegrain telescope at his observatory in southeastern Austria. (Editor's note: For help finding Mars' moons, just put your cursor over the image.)