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APOD: 2008 July 4 - SN 1006 Supernova Remnant

A new star, likely the brightest supernova in recorded human history, lit up planet Earth’s sky in the year 1006 AD. The expanding debris cloud from the stellar explosion, found in the southerly constellation of Lupus, still puts on a cosmic light show across the electromagnetic spectrum. In fact, this composite view includes X-ray data in blue from the Chandra Observatory, optical data in yellowish hues, and radio image data in red. Now known as the SN 1006 supernova remnant, the debris cloud appears to be about 60 light-years across and is understood to represent the remains of a white dwarf star. Part of a binary star system, the compact white dwarf gradually captured material from its companion star. The buildup in mass finally triggered a thermonuclear explosion that destroyed the dwarf star. Because the distance to the supernova remnant is about 7,000 light-years, that explosion actually happened 7,000 years before the light reached Earth in 1006. Shockwaves in the remnant accelerate particles to extreme energies and are thought to be a source of the mysterious cosmic rays.

EO Newsroom: New Images - Smoke Plume

Can you guess what is shown in this photo? What is the plume extending upward from the ground? Why is the top of the plume brighter than its bottom? What is the bright object in the lower righthand corner of the picture, and what is the dark, cone-shaped feature that seems to be leaving the plume and converging on the bright object? Examine the picture carefully, look at the high-resolution version if you want to, and see if you can figure out the answers to these questions. Then, read the caption below to test yourself.

What is the Plume?
This is a photograph of the Space Shuttle (STS-98) launch on February 7, 2001, at 6:13 p.m. eastern time. The whitish plume is the pillar of smoke and steam left behind by the solid rocket boosters. Looking carefully, you can see a very bright dot at the top of the column of smoke, which is the flame still visible at the base of the solid rocket boosters. Even as the Space Shuttle is blasting into orbit, lower-level winds have begun to twist its pillar of smoke.

Why is the top part of the plume brighter?
This photo was taken near sunset, when the sun was relatively low on the western horizon. In the photo, you are looking eastward. The top portion of the plume is much brighter because it is being illuminated directly by sunlight, whereas the bottom portion of the plume lies within the Earth’s shadow.

What is the bright object?
The bright orb in the lower righthand corner of the picture is the full, sunlit face of the moon which has already risen above the eastern horizon.

What is the dark feature?
The dark, cone-shaped feature extending downward and eastward from the pillar of smoke is its shadow, known as the Burgeron Effect (not uncommon when launches are around sunrise or sunset). The shadow exists in the air because there are aerosol particles in the air that reflect and scatter sunlight everywhere except where the sunlight is being blocked by the pillar of smoke. Thus, that part of the sky appears darker.

Why does the shadow point at the moon?
Because the launch took place on the evening of a full moon, any shadow cast would have to appear to end at the moon since the Earth, moon, and sun were naturally in alignment. Remember, you are looking eastward at the moon and the sun is above and behind you in this perspective.

APOD: 2008 July 2 - Night Shinings

In the early morning hours of June 30th, ghostly clouds hovered in the east in this view of near dawn skies over western France. The noctilucent or night-shining clouds lie near the edge of space, reflecting sunlight from about 80 kilometers above Earth’s surface. Usually spotted above the poles in summer, they are now seen with increasing frequency farther from the poles, in this case extending to the photographer’s latitude of about 48 degrees north. The trend could be a telltale sign of global changes in the atmosphere. Another 400,000 kilometers away, the Moon’s sunlit crescent shines brightly, its night side illuminated by Earthshine. Of course, as a bonus for early risers June’s old crescent Moon was followed closely across the sky by the lovely Pleiades star cluster, surrounded by cosmic dust clouds and shining from a mere 400 light-years away.

APOD: 2008 July 1 - Pickering’s Triangle from Kitt Peak

Wisps like this are all that remain visible of a Milky Way star. About 7,500 years ago that star exploded in a supernova leaving the Veil Nebula, also known as the Cygnus Loop. At the time, the expanding cloud was likely as bright as a crescent Moon, remaining visible for weeks to people living at the dawn of recorded history. Today, the resulting supernova remnant has faded and is now visible only through a small telescope directed toward the constellation of Cygnus. The remaining Veil Nebula is physically huge, however, and even though it lies about 1,400 light-years distant, it covers over five times the size of the full Moon. In images of the complete Veil Nebula, studious readers should be able to identify the Pickering’s Triangle component pictured above, a component named for a famous astronomer and the wisp’s approximate shape. The above image is a mosaic from the 4-meter Mayall telescope at the Kitt Peak National Observatory located in Arizona, USA.

APOD: 2008 June 26 - M27: Not A Comet

Born on June 26th in 1730, astronomer Charles Messier scanned 18th century French skies for comets. To avoid confusion and aid his comet hunting, he diligently recorded this object as number 27 on his list of things which are definitely not comets. In fact, 21st century astronomers would classify it as a Planetary Nebula, but it’s not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is now known to be an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star’s outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star’s intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is over 2.5 light-years across and about 1,200 light-years away in the constellation Vulpecula. This impressive color composite highlights subtle jet features in the nebula. It was recorded with a robotic telescope sited in Hawaii using narrow band filters sensitive to emission from oxygen atoms (shown in green) and hydrogen atoms. The hydrogen emission is seen as red (H-alpha) and fainter bluish hues (H-beta).

APOD: 2008 June 14 - M51 Hubble Remix

The 51st entry in Charles Messier’s famous catalog is perhaps the original spiral nebula - a large galaxy with a well defined spiral structure also cataloged as NGC 5194. Over 60,000 light-years across, M51’s spiral arms and dust lanes clearly sweep in front of its companion galaxy (right), NGC 5195. Image data from the Hubble’s Advanced Camera for Surveys has been reprocessed to produce this alternative portrait of the well-known interacting galaxy pair. The processing has further sharpened details and enhanced color and contrast in otherwise faint areas, bringing out dust lanes and extended streams that cross the small companion, along with features in the surroundings and core of M51 itself. The pair are about 31 million light-years distant. Not far on the sky from the handle of the Big Dipper, they officially lie within the boundaries of the small constellation Canes Venatici.