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Sunday, December 31, 2017


The Perigee Moon ("Super Moon") of Tuesday January 2, What Can You See?

The  Full Moon of Tuesday, 2 January is a perigee Moon when the Full Moon is closest to the Earth. This is hot on the heels of the Monday, December 4 perigee Moon.

A full Moon at perigee has been called a "Super Moon", this is not an astronomical term (the astronomical term is perigee syzygy, but that doesn't trip off the tongue so nicely), but an astrological one first coined in 1979 (see here).

Still, it is a good excuse to get people out and looking at the Moon.

Chart comparing the binocular/telescopic appearance of the December 2017 Full Perigee Moon and the 2 January 2018 Full Perigee Moon with the apogee Moon of  July 27 2018, all times are at local astronomical twilight, 90 minutes after sunset. . As you can see the January 2 Perigee Moon is slightly larger than the 4 December 2017 Perigee Moon. Click to embiggen.

While perigee (closest approach) of the Moon is actually during daylight hours on the 2nd, the rising Moon is still closer than the December 4 perigee Moon at its closest approach (356946 km at astronomical twilight vs 357493 km on 4 December at closest approach (which was before the Moon rose here in Australia).

Even so it will be hard to distinguish from most normal full Moons. However, if you have a good memory you should be able to distinguish it from the apogee mini-Full Moon of June 8 2017, or keep it is mind for the upcoming apogee mini-Full Moon 27 July 2018.
However, this will be a good opportunity to image the full moon through telescopes or binoculars. During the night the full Moon will recede from Earth, and images taken at hourly intervals (and at the same scale) should show the Moon shrinking. If you then image the Moon at the same scale on the night of the apogee Full Moon of 27 July, the difference in size will be obvious.

Full details and links to hints on imaging the perigee Moon are at the 4 December Perigee Moon page.

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