From: bcollins@utdallas.edu (ARLIN B COLLINS)
Subject: Sky&Telescope Weekly News Bulletin
Organization: Univ. of Texas at Dallas
Date: Tue, 12 Jan 1993 02:52:17 GMT

****
 SKY & TELESCOPE NEWS BULLETIN -- JANUARY 9

 DEFINITELY DARK MATTER
 More than 1,500 astronomers gathered in Phoenix this past week for the
 winter meeting of the American Astronomical Society. One of the most
 exciting results announced there was the discovery of what appears to
 be a huge reservoir of dark matter in the NGC 2300 group, a trio of
 galaxies in Cepheus. Using the orbiting Rosat observatory, a team led
 by John Mulchaey of the Space Telescope Science Institute observed
 intense X-ray emission from hot gas in the system. The three visible
 galaxies contain far too little mass to keep the gas from dispersing
 into space, so it must be held in place by the gravitational pull of
 unseen matter. Mulchaey and his associates estimate that this dark
 stuff, of unknown origin, is 10 to 30 times more massive than the
 galaxies themselves. If the NGC 2300 group is typical, this could mean
 that most of the dark matter in the universe exists in small groupings
 of galaxies like the one to which our Milky Way belongs. Before this
 discovery, large quantities of dark matter were inferred to exist only
 in rich clusters containing hundreds of galaxies. 

 BETTER BLACKBODY 
 Another important announcement came from scientists working with the
 Cosmic Background Explorer, or COBE, satellite. John Mather of NASA's
 Goddard Space Flight Center presented an improved spectrum of the
 cosmic microwave background radiation, the faint relic of the Big Bang.
 The spectrum is exactly that of a so-called blackbody, or perfect
 radiator, with a temperature of 2.726 degrees Kelvin. The radiation
 deviates from a pure blackbody spectrum by less than 0.03%, compared
 with previous COBE measurements that were uncertain at the 1% level.
 This implies that the eventual formation of large-scale structure in
 the eons after the Big Bang could not have been triggered by explosive
 events such as supernovae from an early generation of stars. Any such
 blasts would have distorted the spectrum of the cosmic background
 radiation. But as COBE has now shown, no such distortions exist. 

 MARS AFTER OPPOSITION 
 Mars reached opposition this past Thursday, hence it is visible all
 night long and is high overhead at midnight. The red planet isn't as
 well situated as it was during the previous two oppositions, so it is
 only about 14 arc seconds in diameter and shines at magnitude minus
 1.4. Mars is easy to find, smack in the middle of Gemini. Observers
 should continue to watch Mars for orographic cloud activity over the
 Tharsis volcanoes. Try looking this week around 5 to 7 hours Universal
 time and use a blue filter. Also, the north polar cap could be starting
 to shine through breaks in its hazy hood. 

 ----- THIS WEEK'S "SKY AT A GLANCE"

 JAN 10 -- SUN
 The waning gibbous Moon rises near Regulus late tonight. 

 JAN 11 -- MON
 The orange-red long-period variable star R Hydrae should be at maximum
 light (4th or 5th magnitude) near this date. 

 JAN 12 -- TUE
 * 

 JAN 13 -- WED
 The nearly last-quarter Moon shines near Jupiter and Spica in the south
 before dawn Thursday morning. 

 JAN 14 -- THU
 Last quarter moon. 

 JAN 15 -- FRI
 Jupiter's moon Io disappears into eclipse a little west of Jupiter
 around 8:07 p.m. Eastern Standard Time. It reappears from occultation
 behind the planet's east limb at 11:31 p.m. EST. 

 JAN 16 -- SAT
 Jupiter's moon Ganymede reappears from eclipse a little southwest of
 the planet around 7:26 p.m. EST. The shadow of Io leaves Jupiter's disk
 14 minutes later. 

 ----- THIS WEEK'S PLANET ROUNDUP

 MERCURY is hidden in the glare of the Sun. 

 VENUS blazes in the southwest as the bright "evening star." 

 MARS, orange and very bright, shines in Gemini near the fainter stars
 Pollux and Castor. Mars was at opposition on January 7th; it rises
 around sunset, glares high overhead in the middle of the night, and
 sets in the west around sunrise. In a telescope its disk appears 14.6
 arc seconds wide. 

 JUPITER, in Virgo, rises around 11:30 p.m. and is the brightest "star"
 in the south at dawn. 

 SATURN is getting very low in the west-southwest at disk, far to the
 lower right of much brighter Venus. 

 URANUS and NEPTUNE are hidden behind the glare of the Sun. 

 PLUTO, extremely faint at 14th magnitude, is low in the southeast
 before dawn. 

 -----
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 provided with permission from Sky & Telescope Magazine.
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-- 
 Arlin B Collins    Mon 11 Jan   Sun   Civil  Naut   Astro
 bcollins@utdallas.edu   rise:  07:31  07:04  06:34  06:04
 lat N32.9 long W096.9    set:  17:40  18:07  18:38  19:07