#2005 june

2005 June 19

Noctilucent Clouds

Credit & Copyright: Pekka Parviainen (Polar Image)

Explanation: Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above. Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark. Pictured above, a network of noctilucent clouds casts a colorful but eerie glow visible above the dark. Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them. Recent evidence indicates that at least some noctilucent clouds result from freezing water exhaust from Space Shuttles.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 22

Saturn's Rings from the Other Side

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What do Saturn's rings look like from the other side? From Earth, we usually see Saturn's rings from the same side of the ring plane that the Sun illuminates them. Geometrically, in the above picture taken in April by the robot Cassini spacecraft now orbiting Saturn, the Sun is behind the camera but on the other side of the ring plane. Such a vantage point gives a breathtaking views of the most splendid ring system in the Solar System. Strangely, the rings have similarities to a photographic negative of a front view. For example, the dark band in the middle is actually the normally bright B-ring. The ring brightness as recorded from different angles indicates ring thickness and particle density of ring particles. Images like these are also interesting for what they do not show: spokes. The unexpected shadowy regions once recorded by the Voyager missions when they passed Saturn in the early 1980s are not, so far, being seen by Cassini. Extra credit: Can you spot the small moon (Prometheus) among the rings?

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 30

Three Planets from Mt. Hamilton

Credit & Copyright: R. Jay GaBany

Explanation: Venus, Mercury, and Saturn wandered close together in western evening skies last week. On Saturnday, June 25, astronomer R. Jay GaBany recorded this snapshot of their eye-catching planetary conjunction, from historic Lick Observatory on Mt. Hamilton, California, USA. The view looks toward the Pacific shortly after sunset with the lights of San Jose and the southern San Francisco Bay area in the foreground. Of course, Venus is the brightest of the trio. Mercury is nearby on the right and Saturn is below and left, closest to the horizon. Farther to the right of the planetary triangle are Pollux and Castor, twin stars of Gemini, with Regulus, bright star of the constellation Leo, at the very upper left corner of the picture. In the coming days, Venus and Mercury remain close, while Saturn continues to drop below them, toward the horizon.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 28

The Giant Radio Lobes of Fornax A

Credit: Ed Fomalont (NRAO) et al., VLA, NRAO, AUI, NSF

Explanation: Together, the radio lobes span over one million light years -- what caused them? In the center is a large but peculiar elliptical galaxy dubbed NGC 1316. Detailed inspection of the NGC 1316 system indicates that it began absorbing a small neighboring galaxy about 100 million years ago. Gas from the galactic collision has fallen inward toward the massive central black hole, with friction heating the gas to 10 million degrees. For reasons not yet well understood, two oppositely pointed fast moving jets of particles then developed, eventually smashing into the ambient material on either side of the giant elliptical galaxy. The result is a huge reservoir of hot gas that emits radio waves, observed as the orange (false-color) radio lobes in the above image. The radio image is superposed on an optical survey image of the same part of the sky. Strange patterns in the radio lobes likely indicate slight changes in the directions of the jets.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 27

Globular Cluster M22 from CFHT

Credit & Copyright: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT

Explanation: The globular cluster M22, pictured above, contains over 100,000 stars. These stars formed together and are gravitationally bound. Stars orbit the center of the cluster, and the cluster orbits the center of our Galaxy. So far, about 140 globular clusters are known to exist in a roughly spherical halo around the Galactic center. Globular clusters do not appear spherically distributed as viewed from the Earth, and this fact was a key point in the determination that our Sun is not at the center of our Galaxy. Globular clusters are very old. There is a straightforward method of determining their age, and this nearly matches the 13.7 billion-year age of our entire universe.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 11

Earth at Twilight

Credit: ISS Crew, Earth Sciences and Image Analysis Lab, JSC, NASA

Explanation: No sudden, sharp boundary marks the passage of day into night in this gorgeous view of ocean and clouds over our fair planet Earth. Instead, the shadow line or terminator is diffuse and shows the gradual transition to darkness we experience as twilight. With the Sun illuminating the scene from the right, the cloud tops reflect gently reddened sunlight filtered through the dusty troposphere, the lowest layer of the planet's nurturing atmosphere. A clear high altitude layer, visible along the dayside's upper edge, scatters blue sunlight and fades into the blackness of space. This picture actually is a single digital photograph taken in June of 2001 from the International Space Station orbiting at an altitude of 211 nautical miles.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 4

First U.S. Spacewalk

Credit Gemini 4 Mission, NASA

Explanation: In 1965, forty years ago on June 3rd, astronaut Edward White made the first U.S. spacewalk. Tethered to his Gemini IV capsule, White is pictured above holding a compressed gas "zip gun" for maneuvers in his right hand. His spacewalk began over the Pacific Ocean near Hawaii and ended 23 minutes later above the Gulf of Mexico. Of course, the term spacewalk is a bit deceiving as White was falling freely in low earth orbit alongside his capsule manned by fellow astronaut James McDivitt. In free-fall, White was able to control his motions by firing bursts from his gun until its supply of compressed gas ran out. He ultimately returned, exhausted, to the two-man Gemini capsule.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC

2005 June 12

M2-9: Wings of a Butterfly Nebula

Credit: B. Balick (U. Washington) et al., WFPC2, HST, NASA

Explanation: Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays as they die. In the case of low-mass stars like our Sun and M2-9 pictured above, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousand of years. M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale. In the center, two stars orbit inside a gaseous disk 10 times the orbit of Pluto. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance. Much remains unknown about the physical processes that cause planetary nebulae.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

NASA Official: Jay Norris.

A service of: EUD at NASA / GSFC