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From: djb@cbosgd.UUCP
Newsgroups: net.astro
Subject: Halley's Comet
Message-ID: <1020@cbosgd.UUCP>
Date: Sat, 25-Feb-84 23:35:14 EST
Article-I.D.: cbosgd.1020
Posted: Sat Feb 25 23:35:14 1984
Date-Received: Sun, 26-Feb-84 23:17:49 EST
Distribution: net
Organization: AT&T Bell Laboratories, Columbus
Lines: 70

I just recently received my copy of the "International Halley Watch
Amateur Observers' Manual for Scientific Comet Studies" (by Stephen J.
Edberg) and am quite pleased.  It is a treasure trove of information on
comet watching in general, and on Halley's Comet and its 1986 appearance.  
The first part of the book is on methods, including information on
visual, photographic, astrometric, spectroscopic and photometric
studies.  The second half contains a day-by-day ephemeris from 6/4/1985
through 5/4/1987, and a sequence of 19 specially modified AAVSO star
charts that show Halley's position in the sky from Nov. 1985 through
May 1986.

In addition, there is a section that describes the International Halley
Watch, an organization that will allow amateur astronomers to network
together and particpate significantly in the study of Halley's Comet.
Forms are included that allow you to register yourself as a member of
the network, and also for recording and reporting your observations.

A quick pass through the book is enough to convince you of the great
discrepancy between the appearance for northern hemisphere observers
and for those in the southern hemisphere.   For example:

 Date 	      Dark Hours vs. Observers Latitude	    Magnitude*
(1986)		45 N.	30 N.	30 S.	45 S.		
-------------------------------------------------------------	(* Recent study
Mar.	7	0.2	0.9	2.0	2.0		4.5	(indicates that
       17	0.5	1.5	3.3	3.7		4.5	(Halley's may be
       27	0.7	2.3	5.3	6.2		4.3	(as much as two
Apr.	6	0	3.8	9.1	9.4		4.0	(magnitudes
       16	6.0	8.3    10.0	9.9		4.4	(brighter than
       26	6.2	8.0	9.2    10.0		5.5	(these values!
-------------------------------------------------------------
Dark hours are the interval during which the Sun is below the local
horizon by at least 18 degrees and the comet is simultaneously visible
above the local horizon.  Notice the difference between the values for
observers at northern latitudes and those at southern latitudes.  As
you would expect from the above table, the altitude of the comet is
similarly much better for southern observers:

 Date		Comet Altitude vs. Observers Latitude
(1986)		40 N.	30 N.	20 N.	20 S.	30 S.
------------------------------------------------------
March	6	 5	10	15	22	22
       16	 8	15	24	40	40
       26	10	20	30	59	60
April   5	 6	15	27	65	73
       10	 -	10	15	49	55
------------------------------------------------------
Altitude is given in degrees at the beginning of morning astronomical
twilight.

I highly recommend this book to anyone planning to take more than
casual notice of Halley's Comet.  It does assume some rudimentary
astronomical knowledge, but encourages any amateur observer to particpate 
in the Halley's Watch network, regardless of skill level or equipment.
Dedication and patience are all that is required.

If you are interested, the book is available through Sky Publishing
(check any recent issue of Sky & Telescope for ordering info).
Me, I'm taking March 1986 off and heading for Australia or New Zealand.


       *         * 
				David Bryant
				AT&T Bell Laboratories
               *		Columbus, OH 43213
            *			(614) 860-4516
	 *  .
            .			djb@cbosgd.UUCP
                		cbosgd!djb@Berkeley.ARPA
       *         *