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Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
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1996 December 21

Sun and Winter Solstice 1996
Credit
: EIT Consortium, SOHO project, ESA, NASA

Today is the Winter Solstice for 1996. After steadily sinking in Northern Hemisphere skies, the Sun is now at its lowest declination - marking the first day of Northern Winter (but Southern Summer!). The Earth is actually closer to the Sun during this season, a fact not usually appreciated by those who dwell on the planet's Northern half. Two days ago, the EIT camera onboard the SOHO spacecraft recorded this image of the Sun in the light of highly ionized Iron atoms. This extreme ultraviolet picture emphasizes magnetic field lines and active regions in the hot plasma above the solar surface. For today's Solar images at many wavelengths, check out the Solar Data Analysis Center's web site.
1996 December 22

18 Miles From Deimos
Credit:
The Viking Project, NASA

Diminutive Deimos is the smallest of the two tiny Moons of Mars. Potato shaped and barely 6 miles wide this asteroid-like body was visited by the Viking 2 orbiter in 1977. This image was made when the spacecraft approached to within 18 miles of Deimos' surface. It is one of the most detailed pictures of a celestial body ever taken by an orbiting spacecraft - the field of view is less than a square mile and features just under 10 feet across are visible. Craters and large chunks of rock are seen scattered on the surface. Some of the craters appear to have been covered by a layer of regolith (soil and broken rock).
1996 December 23

The Hills of Ganymede
Credit:
The Galileo Project, NASA

This computer generated 3D close-up view of Jupiter's large moon Ganymede was created using image data from NASA's Galileo spacecraft. Simulating stereo vision by combining two recent images recorded from different angles, 3 dimensional information was reconstructed for a section of Ganymede's surface. The result shows the furrows, craters, and hills in the region appropriately known as "Galileo Regio" with a resolution of about 250 feet. Currently exploring the Jovian System, the Galileo spacecraft just completed a flyby of Europa. It is scheduled to return to Ganymede in April next year.
1996 December 24

A Mirry Christmas
Credit:
STS-79 Crew, NASA

Thinking about spending the Holiday Season in low Earth orbit? Astronaut John Blaha and his cosmonaut colleagues Valeri Korzun and Alexander Kaleri are doing just that onboard the Russian Mir spacestation. You can e-mail them Seasons Greetings. Blaha replaced Shanon Lucid as a Mir resident during the STS-79 mission flown by the Space Shuttle Atlantis and is scheduled to be replaced by Jerry Linenger when Atlantis makes another shuttle run to Mir during the STS-81 mission. The Mir is seen here 200 miles above the Earth as the sun sets following the latest Atlantis undocking. NASA shuttle flights to the Mir are part of the Phase 1 program for construction of the International Space Station.
1996 December 25

An Earth Ornament
Credit
: The Clementine Project, U.S. Geological Survey

The Apollo 8 astronauts spent the 1968 Christmas Season in lunar orbit, returning with striking images of the Moon and Earth from space which inspired the world. While in lunar orbit in 1994, the prospecting Clementine spacecraft also turned its cameras toward the home world - the result was this mosaic of 70 high resolution images of our planet from a cosmic perspective. The swirling clouds and dramatic colors give the Earth the appearance of a delicate, painted ornament hanging in space. Best Wishes and Seasons Greetings!
1996 December 26

Carl Sagan 1934-1996
Credit and Copyright
: 1994 by Michael Okoniewski

Carl Sagan died last Friday at the age of 62. Sagan was the world's most famous astronomer. Among his many activities as a scientist, he contributed to the discovery that the atmosphere of Venus is prohibitively hot and dense, and found evidence that Saturn's moon Titan contains oceans stocked with the building blocks of life. Sagan was an outspoken proponent of the search for extra-terrestrial life, including sending probes to other planets and listening with large radio telescopes for signals from intelligent aliens. Sagan's outstanding ability to explain allowed almost a billion people to better understand the cosmos in which they live.
1996 December 27

HET: The New Largest Optical Telescope
Credit:
UT Austin, PSU, Stanford, GAUG, & LMUM

Most of our universe is too dim to see. To peer into our cosmos' unknown depths, astronomers must deploy new tools - and the classic new tool is a larger telescope. Pictured above is the new Hobby-Eberly Telescope (HET) which recently declared "first light" in western Texas. HET currently has the largest single mirror of any optical telescope -- 11 meters in diameter. Telescopes in space, like the Hubble Space Telescope, are much smaller but avoid the Earth's atmosphere blurring out fine detail. HET's huge size, on the other hand, allows it to see very dim objects and determine their spectrum. HET's unusual design allows the primary mirror to stay put during an observation! Only smaller focusing instruments suspending above the primary move to track an astronomical object.
1996 December 28

CG4: A Ruptured Cometary Globule
Credit and Copyright
: David Malin, Anglo Australian Observartory

The odd looking "creature" to the right of center in the above photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails. These features cause cometary globules to have visual similarities to comets, but in reality they are very much different. Cometary globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not completely known. The galaxy to the left of center is very far in the distance and is only placed near CG4 by chance superposition.
1996 December 29

Dark Bok Globules in IC 2944
Credit and Copyright
: David Malin, Anglo Australian Observartory

The dark spots in the above picture are not photographic defects but an unusual type of interstellar cloud known as a Bok globule. Bok globules, named after astronomer Bart Bok who studied them extensively, are small dark clouds made of gas and dust that are typically condensing to form a star or stars. These Bok globules are found in front of a glowing H II region known as IC 2944.
1996 December 30

X-Ray Earth
Credit:
Polar, PIXIE, NASA

The Earth glows in many kinds of light, including the energetic X-ray band. Actually, the Earth itself does not glow - only aurora produced high in the Earth's atmosphere. Above is the first picture of the Earth in X-rays, taken in March with the orbiting Polar satellite. Bright X-ray emission is shown in red. Energetic ions from the Sun cause aurora and energize electrons in the Earth's magnetosphere. These electrons move along the Earth's magnetic field and eventually strike the Earth's ionosphere, causing the X-ray emission. These X-rays are not dangerous because they are absorbed by lower parts of the Earth's atmosphere.
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1996 December 31

Io Rotating
Credit:
The Galileo Project, JPL, NASA

Are any volcanoes on Io currently erupting? To help answer this, scientists instructed the robot spacecraft Galileo to take hourly pictures of this moon of Jupiter prior to its most recent encounter. The most obvious changes in Io are due to the changing amount of sunlight reflected from the moon to the spacecraft. More careful inspection does verify continuous volcanic plumes. The most prominent plume visible is from Prometheus, visible just below Io's equator. This plume was first photographed in 1979 by Voyager, so Prometheus appears to have been erupting continuously for at least 18 years! On most browsers, the above picture will appear animated. To stop the movie, click on your broswer's "stop" button.
1997 January 1

Aurora Over Circle, Alaska
Credit and Copyright:
Dick Hutchinson

Aurora can make spectacular sights. This particular aurora was photographed hovering over the town of Circle, Alaska. Although Aurora might first appear to be moonlit clouds, they only add light to the sky, and hence can not block background stars from view. Called "northern lights" in the northern hemisphere of the Earth, aurora are caused by charged particles streaming from the Sun entering the Earth's atmosphere. If viewed from space, aurora glow in X-ray light as well as in the visible! Several WWW sites can tell you if aurora are predicted to be visible in your area.
1997 January 2

Bubbles and Arcs in NGC 2359
Credit and Copyright:
P. Berlind & P. Challis (CfA), 1.2-m Telescope, Whipple Obs.

What caused the bubbles and arcs in NGC 2359? The main suspect is the Wolf-Rayet star in the center of one of the bubbles - visible slightly below and to the right of the center of the above photograph. Most Wolf-Rayet stars are known to be massive, highly luminous stars that continually cast off material in a stellar wind - which commonly form bubbles in the interstellar medium. But the unusual structure of the NGC 2359 arcs indicate something more complex is going on. Is the star moving supersonically? Is there another energetic star in the vicinity? Future observations may give more pieces to this picturesque puzzle.
1997 January 3

A Wolf-Rayet Star Blows Bubbles
Credit and Copyright
: P. Berlind & P. Challis (CfA), 1.2-m Telescope, Whipple Obs.

Wolf-Rayet stars can blow bubbles. These unusual stars are much hotter and more luminous than our Sun. All extremely massive stars will eventually evolve though a Wolf-Rayet phase. Approximately 200 Wolf-Rayet stars are known in our Milky Way Galaxy. Wolf-Rayet stars generate bubbles because they continually eject their outer atmosphere as a stellar wind. This outgoing wind of particles typically carries away more than the mass of our Earth each year! The wind is caused by atmospheric particles absorbing outgoing starlight, although many details of this process are unknown. The Wolf-Rayet is the brightest star in the above picture and is in the center of the large bubble in the nebula known as NGC 2359.
1997 January 4

A Star Where Photons Orbit
Credit and Copyright
: Robert Nemiroff (MTU)

The above computer animated picture depicts how a very compact star would look to a nearby observer. The star pictured is actually more compact that any known except a black hole, so it is only hypothetical. The observer is situated at the photon sphere, where photons can orbit in a circle. To help the viewer better visualize the great distortions created by gravity, a map of the Earth was projected onto the star, and a map of the familiar night sky was projected above. From here one can either look down and see several duplicate images of the entire surface of the star, look up and see several duplicate images of the entire night sky, or look along the photon sphere and see the back of one's own head.
1997 January 5

Too Close to a Black Hole
Credit and Copyright
: Robert Nemiroff (MTU)

What would you see if you went right up to a black hole? Above are two computer generated pictures highlighting how strange things would look. On the left is a normal star field containing the constellation Orion. Notice the three stars of nearly equal brightness that make up Orion's Belt. On the right is the same star field but this time with a black hole superposed in the center of the frame. The black hole has such strong gravity that light is noticeably bent towards it - causing some very unusual visual distortion. In the distorted frame, every star in the normal frame has at least two bright images - one on each side of the black hole. In fact, near the black hole, you can see the whole sky - light from every direction is bent around and comes back to you. Black holes are thought to be the densest state of matter, and there is indirect evidence for their presence in stellar binary systems and the centers of globular clusters, galaxies, and quasars.
1997 January 6

Blue Sun Glaring
Credit:
EIT, SOHO, ESA, NASA

The Sun is a bubbling ball of extremely hot gas. In this false-color picture, light blue regions are extremely hot - over 1 million degrees, while dark blue regions are slightly cooler. The camera filter used was highly sensitive to the emission of highly charged iron ions, which trace the magnetic field of the Sun. The rich structure of the image shows the great complexity of the Sun's inner corona. A small active region can be seen just to the right and above center. This picture was taken in ultraviolet (extremely blue) light by the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft, which is orbiting the Sun just ahead of the Earth, at the L1 point. SOHO was launched in 1995 and will continually monitor the Sun for several years.
1997 January 7

Red Sun Streaming
Credit
: LASCO, SOHO, ESA, NASA

The Sun is leaking. In fact, it is gushing: particles stream away from the Sun at hundreds of kilometers per second. Some of these particles strike the Earth and cause aurora. Most particles, however, either surround the Sun as a huge solar corona or glide into interstellar space as the solar wind. Don't worry about the Sun totally evaporating - it loses too little mass to have any lasting effect. The above false-color picture was taken with the Large Angle and Spectrometric Coronograph on board the SOlar and Heliospheric Observatory (SOHO). This instruments blocks out the central solar disk so it can image the regions surrounding the Sun. The large streamers visible are typical. Where these charged ions get their enormous streaming energy is still a mystery!
1997 January 8

Grey Sun Seething
Credit:
Big Bear Observatory, Caltech

The Sun's surface is not smooth. It has thousands of bumps called granules and usually a few dark depressions called sunspots. Each of the numerous granules is the size of an Earth continent, but much shorter lived. A granule can only be expected to last a few minutes before dissipating and being replaced by a newly rising granule. In this way a granule acts much like a rising bubble in boiling water. The above black and white, visible-light picture is quite unusual because the usual relative darkening visible near the edges of the Solar disk have been digitally removed. Visible near the center are two large sunspots while the computer enhancement brings out two bright plages close to the right solar limb.
1997 January 9

Hazing Jupiter
Credit
: The Galileo Project, JPL, NASA

A dramatic mosaic of recent images from the Galileo spacecraft reveals details of swirling clouds and a thick stratospheric haze in the atmosphere of Jupiter, the Solar System's largest planet. This false color representation is keyed to altitude - red indicates cloud features near the top of the gas giant's extensive atmosphere while blue corresponds to features at depth. North is up in the mosaic, centered at about 50 degrees northern Jovian latitude, and the limb or edge of the planet arcs across the upper right. The line of sight looking toward the limb emphasizes the high altitude, red haze. What causes the red haze? It may well be created as energetic electrons and other charged particles swept up by Jupiter's magnetosphere are funneled along magnetic field lines and bombard the atmosphere near the polar regions. Charged magnetospheric particles can also create Aurora.
1997 January 10

Eclipsed Moon in Infrared
Credit:
DCATT Team, MSX Project, BMDO

Last September's total lunar eclipse disappointed many observers in the Eastern and Midwestern US who were cursed with cloudy skies. However, the Midcourse Space Experiment (MSX) satellite had a spectacular view from Earth orbit and SPIRIT III, an onboard imaging infrared telescope, was used to repeatedly image the moon during the eclipse. Above is one of the images taken during the 70 minute totality, the Moon completely immersed in the Earth's shadow. Infrared light has wavelengths longer than visible light - human's can not see it but feel it as heat. The bright spots correspond to the warm areas on the lunar surface, dark areas are cooler. The brightest spot below and left of center is the crater Tycho, the dark region at the upper right is the Mare Crisium. The series of SPIRIT III images allow the determination of cooling curves for geologically different areas, exploring the physical properties of the Moon's surface.