A spectacularly bright moon will illuminate the sky tonight. It’s called the harvest moon — the closest full moon to the autumn equinox in the Northern Hemisphere. Depending on the year, the harvest moons arrives anywhere from two weeks before to two weeks after the autumn equinox. This particular harvest moon will come 6 days shy of the 2016 equinox.
Some people believe that the harvest moon appears larger or more colorful than usual. While reports of the size difference may simply reflect people’s expectations of something special from the moon on this particular night, the moon may appear more orange because it rises closer to the horizon than usual, causing it to take on a yellow, orange, or red hue.
But what’s really special about the harvest moon is that, during this the time of year, the time difference between moonrises on successive evenings is at its yearly minimum. All of that extra light in the evenings has traditionally given farmers extra time to harvest their fall crops.
This year’s harvest moon may also be a supermoon, which is a full moon occurring at the closest point to Earth on its elliptical orbit. However, there is some uncertainty in assigning the status of supermoon, as it is unclear whether the definition refers to the closest point over a given month, or the entire year. If we look at the monthly orbit, tonight’s moon will be a supermoon, but relative to its yearly orbit, it won’t quality for the designation.
Finally, a subtle lunar eclipse, visible to sky gazers in parts of Europe, Asia, Australia and the Western Pacific, will accompany tonight’s harvest moon.
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