#184 Tomorrow's picture: December 20, 1995
“Sometimes it takes a keen eye to see a good mirage. Around the center of the red galaxy image in the above photograph lie four blue "smudges." Each smudge is actually a different image of the same background quasar. The central galaxy happens to fall directly in the light path of the quasar. Consequently, the huge mass of the galaxy is able to pull separate images of the quasar around it - an effect called gravitational lensing. Hence we see a gravitational mirage! Astronomers have hopes of using light differences between these quasar images to not only "weigh" the central galaxy but even provide clues about the expansion rate and composition of the universe."
Copyright: Public domain
#185 Tomorrow's picture: December 21, 1995
“In the center of the glowing red gas on the Trifid Nebula lies an open cluster of young hot stars. The energetic light from these stars strikes hydrogen atoms in the surrounding nebula causing them to lose their electrons. When an electron finds its way back to a hydrogen proton, it emits light at very specific colors - one of which is the red color of the nebula seen here. The red glow is thus indicative of an emission nebula. The dramatic dark sheets are made of interstellar dust grains, tiny needle shaped pellets which are thought to be created and expelled in the atmospheres of cooler stars."
Copyright: Anglo-Australian Telescope
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#186 Tomorrow's picture: December 22, 1995
“December 22 marks the"
Copyright: Public domain
#187 Tomorrow's picture: December 23, 1995
“The third and fourth innermost moons of Saturn were unexpectedly discovered to be gravitational "shepards." The inner moon Prometheus and the outer moon Pandora use their gravitational attraction to define Saturn's outermost ring. Were any of the smaller chunks of ice and rock that compose Saturn's F Ring to stray, the ring particle would be gravitationally pulled back into place by one of these passing moons. This complex interaction creates a ring structure with two narrow braids and several unusual knots."
Copyright: Public domain
#188 Tomorrow's picture: December 24, 1995
“NASA's robot spacecraft Voyager 2 passed the planet Uranus and its moons in 1986. While the cloud tops of Uranus proved to be rather featureless, the surface of Miranda, the innermost of Uranus' large moons, showed several interesting features. Voyager 2 passed closer to Miranda than to any Solar System body and hence photographed it with the clearest resolution. Miranda's heavily cratered terrain shows grooves like Jupiter's moon Ganymede and several valleys and cliffs. Miranda is made of a roughly equal mix of ice and rock. Miranda was discovered by Gerard Kuiper in 1948."
Copyright: Public domain
#189 Tomorrow's picture: December 25, 1995
“During the 1968 Christmas season Frank Borman, James Lovell, and William Anders flew the Apollo 8 command module From the Earth to the Moon and back (launched Dec. 21, achieved 10 lunar orbits, landed Dec. 27). The Apollo 8 mission's impressive list of firsts includes; the first manned flight using the Saturn V rocket, the first humans to journey to the Earth's Moon, and the first to photograph the Earth from deep space."
Copyright: Public domain
#190 Tomorrow's picture: December 26, 1995
“Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems. In a binary system, the higher mass star will evolve faster and will eventually become a compact object - either a white dwarf star, a neutron star, or black hole. When the lower mass star later evolves into an expansion phase, it may be so close to the compact star that its outer atmosphere actually falls onto the compact star. Such is the case diagrammed above. Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. Gas in the accretion disk swirls around, heats up, and eventually falls onto the compact star. Extreme conditions frequently occur on the surface of the compact star as gas falls in, many times causing detectable X-rays, gamma-rays, or even cataclysmic novae explosions. Studying the extreme conditions in these systems tells us about the inner properties of ordinary matter around us."
Copyright: Public domain
#191 Tomorrow's picture: December 27, 1995
“In 1992 a tremendous explosion occurred in the constellation of Cygnus. Dubbed Nova Cygni 1992, this event most probably occurred in an accretion disk binary system. Astronomers hypothesize that this system's white dwarf had so much gas dumped onto it's surface that conditions became ripe for nuclear fusion. The resulting thermonuclear detonation blasted much of the surrounding gas into an expanding shell. The Hubble Space Telescope photographed this expanding shell in 1994. Nova Cygni 1992 was the brightest nova in recent history - at its brightest it could be seen without a telescope. It was observed in every part of the electromagnetic spectrum."
Copyright: Public domain
#192 Tomorrow's picture: December 28, 1995
“Sometimes even galaxies can suffer a fatal attraction. Here gravity causes two galaxies to collide in a spectacular display of energetic gas, dust, and light. When galaxies collide it is rare that any stars in the galaxies themselves collide, or that any change will be seen in a human lifetime. Rather the structure of one or both galaxies gets slowly disrupted, while interior gas condenses to new star forming regions. Stellar motions in the center of the NGC 6240 frenetic mix are among the highest in any stellar system. Galaxy mergers may emit energetic radiations across the electromagnetic spectrum. This galactic jumble is, in fact, extremely bright in infrared light."
Copyright: Public domain
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