Event Date: September 28th
Time: 6:30 PM
Brief
We approach the harvest moon over the next several hours, as it will be the closest full moon to the September equinox. A little less than a week ago was the equinox, and the small intervals between moon rises over the last few days, remind us why this Moon gets its name. As a reminder, the Moon increases in declination as it becomes full this month and next. As it does, it spends less time below the horizon and above it to provide light after Sunset. This was--and still may be today in many parts of the world--significant for farmers to finish their harvest. Even the few days following a full Moon have it big enough to provide enough light. Even more importantly, the full Moon and gibbous-phase ones sandwiching it spend alot of time high in the sky, making that light a little more helpful.
Here is the Moon already above the horizon as a 99% waxing gibbous before the Sun goes down, with its orbit, celestial equator and ecliptic showing also.
Time: 6:30 PM
Brief
We approach the harvest moon over the next several hours, as it will be the closest full moon to the September equinox. A little less than a week ago was the equinox, and the small intervals between moon rises over the last few days, remind us why this Moon gets its name. As a reminder, the Moon increases in declination as it becomes full this month and next. As it does, it spends less time below the horizon and above it to provide light after Sunset. This was--and still may be today in many parts of the world--significant for farmers to finish their harvest. Even the few days following a full Moon have it big enough to provide enough light. Even more importantly, the full Moon and gibbous-phase ones sandwiching it spend alot of time high in the sky, making that light a little more helpful.
Here is the Moon already above the horizon as a 99% waxing gibbous before the Sun goes down, with its orbit, celestial equator and ecliptic showing also.
Detailed
Although our satellite is just barely north of the celestial equator, it will slowly move further north and east against the stars. Looking at the angle of the ecliptic with the celestial equator and horizon, that is a reminder, as well as the Moon's orbit still a few degrees north of the ecliptic. Although the Moon approaches descending node this week, that will only partially slow down its declination "rise" north.
A few years ago, we were seeing an even more interesting scenario, in which the Moon's ascending node was closer to this part of the sky, and the time between rises was a few minutes less than now. Moonrise is officially seconds before 6:40 PM, and tomorrow, can you predict what time it will be? Taking our latitude into account as well as what I mentioned about the Moon's position on the celestial equator, try taking a guess. I will show it again tomorrow very near full the crest of fullness, on the rise.
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