ASTRONOMICAL CALENDAR
CALENDAR EXPLANATIONS
The calendar should well serve most North Americans, although the calculations are most exact for Arlington Heights, Illinois. The North American Central Time Zone is utilized with the appropriate standard or daylight considerations.
The Moon is depicted for the night of the two dates the image straddles. A waxing Moon is shown as it would appear midway between sunset and moonset. A waning Moon is shown as it would appear midway between moonrise and sunrise. Not only depicted is the fraction of the lunar disk that is illuminated, but also the apparent tilt, angular size, earthshine and oppositional flash.
The Moon phases in the lower right do not represent the simplistic geocentric
ecliptical longitude elongations normally published. Instead they are based on the
illuminated fraction of the apparent lunar disk as viewed from Arlington, Heights
Illinois. Half the time that would be as viewed through the Earth by a fictional
X-
A Full Moon’s brightness is noted with the formula of Jean Meeus, for which a Full Moon’s ecliptical latitude is among the important factors. The standard for brightness is 1.00 when the Moon and Sun are at their mean distances from Earth, and the Moon is in exact opposition to the Sun in both ecliptical longitude and latitude. Of course that would only occur during a lunar eclipse, so in the case of a lunar eclipse the Full Moon is assumed to be just outside the Earth’s penumbra.
Mingled with the phase dates are the dates for perigee and apogee. Those are geocentric. If instead calculated for a specific location on the Earth’s surface, the distance would gyrate daily as the Earth rotates.
For the planets, a midnight star is a planet above the horizon at local midnight, i.e. the time midway between sunset and sunrise. A morning star is a planet which at sunrise is either above the western horizon or at least 10° above the eastern horizon. An evening star is a planet which at sunset is either above the eastern horizon or at least 10° above the western horizon. A planet could be all three during a single night. If none of these, then it appears close to the Sun and is listed as lost in glare.
If on a single date there is comment similar to Mercury 0.7° Regulus, that means Mercury is in conjunction with Regulus and will pass it by 0.7°. Conjunctions and oppositions of planets relative to the Sun are also noted on the appropriate dates. Transits and greatest eastern and western elongations are noted for Mercury and Venus. Eclipses and major meteor showers are noted, as are occultations of planets and stars by the Moon. If a number appears in parentheses, that indicates a date other than the one on which the event is displayed.
© Curt Renz
