Fall 2006 Issue
Moondata Update 2007
One of the
most important factors in EME communications is knowing when
By Derwin King, W5LUU
The Earth-Moon distance and the cosmic (sky) noise temperatures in the direction of the Moon are predictable, cyclical variables that set the basic day-to-day quality of Earth-Moon-Earth (EME) communications for frequencies below 1.0 GHz. The best conditions occur when: (1) the Range Factor (Earth-Moon distance) is at an absolute minimum, and (2) the Sky Temperature behind the Moon, as viewed from Earth, is the coldest along the moon path. While Range Factor is frequency independent, Sky Temperature rapidly decreases with frequency, up to ~1 GHz, and levels out. The EME signal-to-noise ratio, in dB, is usually degraded from the ideal by a factor (DGRD, see below) which varies over hourly, daily, weekly, monthly, and yearly time periods. The DGRD factors, in dB, for 144 and 432 MHz, and other pertinent EME data, are tabulated in the W5LUU Weekend Moondata for 0000 UT on each Sunday of the upcoming year and provide a general guide to the basic EME weekend conditions (see the accompanying table). Ionospheric disturbances, local noise, and polarization mismatch will increase the “apparent” DGRD.
Get active on EME by 2007. Conditions will
improve over the next three years as Moon perigees are at +declinations
and approach the best cold sky region (8–9 hr. RA) at ~ 2.7 hrs RA per
year. These will peak in 2010 and then begin to decrease, but will still
be good for approximately two more years. In 2007 two Very Good and four
Good weekend days will occur in the first half of the year, and seven in
the second half. Some days during the week may be rated better. Several
weekends between September 2 and November 25 look good for the 2007 fall
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, plus and minus, ranges from 18.15 up to 28.72 degrees with a period (maximum to minimum and back to maximum) in about 19 years. The last maximum was on 09/15/2006.
RA (hrs): Right Ascension, in hours,
gives the east-west position of the Moon against the sky background. The
average period of RA cycle is 27.321662 days, but it can vary by a day or
so due to the Earth and Moon motion.
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