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Full moon tonight, or last night?

Tonight – January 24, 2016 – many will look outside and think they’re seeing a full moon. In fact, they’re seeing a waning moon.

According to astronomers, those sticklers for detail, there’s only one instant when the moon turns precisely full. It’s when when the moon is 180o opposite the sun in ecliptic longitude.

It’s the same instant worldwide, and, for us in the Americas, it was last night. That is, this month’s moon turned precisely full on January 24, 2016, at 1:46 Universal Time. According to clocks in the Americas, it was January 23 at 8:46 p.m. EST, 7:46 p.m CST, 6:46 p.m. MST and 5:46 p.m. PST.

So the moon is one day past full as it beams at early evening on January 24. No matter. The waning gibbous moon will still appear plenty full to the eye.

Want more precision? The lunar disk is 98.9% illuminated by sunshine on January 25 at 1:46 Universal Time (North American time zones: January 24 at 8:46 p.m. EST, 7:46 p.m CST, 6:46 p.m. MST and 5:46 p.m. PST).

Click here and you can also find that the waxing gibbous moon was 98.9% illuminated one day before the January, 2016, full moon (January 23 at 1:46 Universal Time).

So, no matter where you live on the globe, watch for a full-looking – but possibly already waning – moon to light up the nighttime nearly all night long. Tonight’s moon shines in the east at early evening, climbs highest up for the night around midnight and sits low in the west at the break of dawn.

Day and night sides of Earth at the instant of the January 2016 full moon (2016 January 24, at 1:46 Universal Time).

Day and night sides of Earth at the instant of the January, 2016, full moon (2016 January 24 at 1:46 Universal Time).

Beginning around January 20 - through mid-February - you can see five bright planets at once in the predawn sky.

In late January – through mid-February – you can see five bright planets at once in the predawn sky. We haven’t been able to see five planets simultaneously since 2005. Read more.

Bottom line: There’s only one instant when the moon turns precisely full in January, 2016. It’s the same instant worldwide. That instant occurred on January 24, 2016, at 1:46 Universal Time. For us in the Americas, it was last night.

Bruce McClure

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