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Fall 2004 Issue |
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Moondata Update 2005
By Derwin King,* W5LUU |
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While a number of factors affect EME communications, the distance from the Earth to the Moon and the cosmic-noise temperature in the direction of the Moon are predictable, cyclical variables that set the basic day-to-day quality of the Earth-Moon path. Other effects being equal, best EME conditions occur when: (1) the Earth-Moon distance is at the absolute minimum; and (2) the moon is positioned, in RA and DEC (see definitions below), in the coldest part of the sky along the Earth-Moon path. In practice, this ideal occurs very rarely, and the EME signal-to-noise ratio is reduced by the DGRD factor (see below), which varies relatively slowly, but continuously with time. DGRD along with other pertinent data are tabulated in the accompanying table for each Sunday at 0000 UT to provide a guide to weekend EME conditions—particularly for 144 and 432 MHz. In 2005 the average DGRD remains higher than normal as Moon perigee occurs at southern declinations in the region of high sky noise (temperature), and Moon apogee occurs near the maximum lunar northern declination. There are no Good weekend days before May 15. However, after mid-year conditions improve somewhat. From May 15 – November 11 there are three Very Good and five Good weekends, but all of these have low declination and are not ideal contest dates. Selection of contest dates will again be a problem and a compromise in 2005.
EME conditions will improve slowly over the
next two years as perigee, on the average, moves ~ 2.7 hours RA per year
along its ~9 year cycle. In 2007–10 DGRD will be much lower for many days
each month as perigee occurs at north declinations and within a few hours
of cold sky.
DEC (deg): Moon declination in degrees north
and south (–) of the equator. This is cyclical with an average period of
27.212221 days. The maximum declination during a monthly cycle is also
cyclic, with a range of 18.15 to 28.72 degrees and a period of about 19
years. The next maximum will be in September 2006. |
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