660921Occultation1_p1

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                     THE ROYAL ASTRONOMECAL SOCIETY OF CANADA

                                                                      Bulletin No. 1
                             LUNAR OCCULTATIONS SECTION


This bulletin is one of several to be issted reporting the activities of the Lunar
Occultations Section. It is hoped that through this bufletin a number of Centres
will be encouraged to participate in this fascinating and useful program. Wherever
a Centre has not already done so, I would ask that the name of a member be submitted
who can provide a liaison between the Centre and the Lunar Occultations Co-ordinator.
Proper recognition can then be given to those already active in the program and a
means provided whereby new observing groups can be established. Please appoint
your representative no later than your October meeting.


Why observe lunar occultations?

The precise timing of the moon crossing our line of sight to a star is valuable in-
formation which the amateur can provide to the professional astronomer. The irregular
period of rotation of the earth was first discovered from occultation timings. The
small variation in its rotation period led to the introduction of ephemeris time.

Analysis of occultation work may reveal in the future the effect on the earth's
period of rotation of glaciation and internal crust movements. Man' s activities
on the moon will require an accurate determination of the details of the orbit of
our satellite which can also be obtained from lunar occultations.  The observation
of "grazes", where the star skirts the edge of the moon's limb, are now considered
important as they provide precise information on the moon's celestial latitude and
polar topography.


What equipment is required?

Occultation predicti ons supplied by the H.M. Nautical Almanac Office, Royal Green-
wich Observatory, generally covers these events for stars brighter than +7.5;
therefore, a relatively small telescope can be used. Magnifications from 50 to
200 are most common. In addition to the telescope, a stopwatch reading to 1/10 sec.
is required. A short-wave radio should be used to monitor the radio time signals
from WWV in Washington or CHU in Ottawa. If a radio is not available on the
observing site, a telephone call to a friend with a short-wave radio would be quite
acceptable. A small photograph or drawing of the full moon is useful in determining
the position angle of the star's disappearance. This is the point on the edge of
the moon's disk where the star makes "contact", and is measured in degrees (through
360°) from the North through East. "Fixes" may be made on certain lunar craters
to obtain position angles with reasonable accuracy.


How do you get started in observing lunar occultations?

After acquiring the necessary physical equipment - telescope, stopwatch and radio -
occultation predictions for your locality are required. In the OBSERVER'S HANDBOOK
occultations are listed for Halifax, Montreal, Toronto, Winnipeg, Edmonton and Van-
couver. If you are located within 300 miles of any of these cities, these predic-
tion times may be used but will only be approximate for your station. A mOre precise