From: parish@cactus.org (Tom Parish)
Subject: SKYWATCH Dec 27-Jan 2 "New Year, Same Days"
Followup-To: poster
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date: Sat, 26 Dec 1992 00:49:02 GMT

SKYWATCH                                                     Turning Point
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This Week      December 27-January 2  "New Year, Same Days"
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Events         * Mercury is too near the sun to be seen. It reappears in
               the southeastern evening sky in early February. 
 
               * Venus is the bright "evening star" low in the southwest
               after sunset.
 
               * Mars rises just after sunset in the constellation Gemini.
 
               * Jupiter rises late in the evening in Virgo.
               
               * Saturn is very low in the southwest at sunset in
               Capricornus.
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December       27 Saturn is south of the crescent moon in the
                  southwest after sunset.
               
               28 Venus is south of the crescent moon in the
                  southwest after sunset.
               
               29 The moon is at apogee, 404,070 km (251,076 mi).
               
               31 First quarter moon.
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"Calendar      You may not realize it but the calendar you're about to
 Days"         switch out is one of the oldest and most reliable
               time-keeping devices of our civilization. In fact, it dates
               back over 400 years, to 1582, when Pope Gregory XIII set 
               out to reform the Julian calendar, which had been the
               calendar of choice since its establishment in 45 BC by
               Julius Caesar. The Julian calendar was based on the number
               of days between successive risings of the bright star
               Sirius just before sunrise (known as a "helical rising").
               This period amounted to 365.25 days. To keep synchronized
               with the seasons, the Romans addd a leap year ofn 366 days
               once every four years when the year was divisible by four.
               
               The problem with the Julian calendar was that it was 11
               minutes longer than the then-adopted length of the tropical
               year (the period from equinox to equinox) of 365.2421 days.
               While 11 minutes a year doesn't sound like much, the
               discrepancy worked out to a gain of more than 10 days in 
               1,600 years. In 1582, for example, the first day of spring
               occurred on March 11.
               
               Pope Gregory's reform recalibrated the calendar by omitting
               10 days in October. Thus, Thursday, October 4, 1582, was
               followed by Friday, October 15. Pope Gregory's modification
               brought everything back in step with the seasons, and also
               shifted the Vernal Equinox back to its rightful date of
               March 21.
               
               Additionally, a new, slightly longer length for the tropical
               year was adopted: 365.2422 days. This was just 0.0078 days
               shorter than the Julian year and amounted to a discrepancy
               of 3.14 days every 400 years. Pope Gregory therefore
               decreed that a century year could only be a leap year when 
               it is exactly divisible by 400. This meant that 3 out of 4
               century years would not be leap years. Such a system
               ensures that the calendar only moves out of step with the
               equinoxes by one day every 3,000 years.
               
               Subdividing the months are the weeks. But unlike the
               tropical year, the seven-day week is largely an arbitrary
               unit of time. The Egyptians had a 10-day week; ancient Rome
               a 9-day week. The 7-day week we observe today may have been
               derived from the interval of days between the four main 
               phases of the moon, which is approximately 7 days.
               
               Unfortunately, the time it takes for Earth to complete one
               orbit around the sun is an odd number of days. This,
               combined with the necessity of adding in an extra day for
               leap years, constantly shifts the dates over the calendar
               grid. Eventually, though, the years cycle around and the
               days and dates match up again with previous years. A
               calendar from 1981 would have sufficed for 1992. If you
               hang on to your 1992 calendar, you'll find it useful again
               in 1998 and 2009. Just scratch off the year, that's the only
               thing that won't repeat itself.
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Author         Jeff Kanipe. Jeff is also editor of Star Date Magazine.
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Publisher      McDonald Observatory at the University of Texas at Austin.
               ___________________________________________________________
     
For More       Write to Star Date at 2601 University, Room 102, the 
Information    University of Texas at Austin, Austin, TX 78712
               ___________________________________________________________
 
Contacts       sandi@astro.as.utexas.edu   Star Date Radio Station Contact
               kanipe@astro.as.utexas.edu  Editor Star Date Magazine
               damond@astro.as.utexas.edu  Star Date scripts contact
               ___________________________________________________________
 
Legal          Copyright 1992 The University of Texas McDonald Observatory.
               Material is intended for personal education and should not 
               be rebroadcast in any written or verbal form without 
               prior permission from the University of Texas.
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Provided by                T H E  T U R N I N G   P O I N T
                               *** Home of Star Date ***
  
                                  HST/DS 512-219-7828
                                  HST/DS 512-219-7848
 
                                   parish@cactus.org
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FINAL ISSUE!!! Termination of SKYWATCH is expected soon.  I have recently
               been informed by Jeff Kanipe that due to low readership
               of this weekly publication he has decided to discontinue 
               writing SKYWATCH.  However, his rational is based on 
               low readership in conventional magazines and newspapers.
 
               Jeff is not aware of the the readership that follows 
               SKYWATCH on USENET, FIDONET, and locally in Austin on 
               the Turning Point BBS.  My opinion is that readership 
               for Jeff's SKYWATCH publication on the networks is huge.
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So Vote !      So VOTE now.  Send Jeff Kanipe a note to tell him you
               want to continue seeing his weekly column on the net.
 
               Send Email to: kanipe@astro.as.utexas.edu
 
               Let's keep this column alive.  It's a labor of love for 
               Jeff.  I format and upload SKYWATCH for the same reasons.
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