Prepare for the third and final supermoon of 2025 this month. Also known as the Cold Moon (a nod to winter’s arrival), it will appear full on December 4 and slightly bigger than usual due to its position around Earth. The Cold Moon will also be high in the night sky because a winter full Moon mirrors the Sun, which is heading toward the solstice on December 21. Since the Sun is at its lowest in December during the solstice, the full Moon will be at its highest point.
What is a supermoon?
A supermoon occurs when a full Moon coincides with its closest approach to Earth on its 27-day orbit. The Moon circles our planet on an elliptical path, which sometimes brings it closer to Earth and sometimes takes it farther. When it’s at the closest point, the Moon is at perigee and when it’s the farthest, that’s called being at apogee.
According to NASA, the Moon’s closest distance to Earth is about 3,63,000 km whereas it’s more than 4 lakh km away at the farthest.
But the interesting thing is, all supermoons do not occur exactly at the moment of perigee. Scientists say the Moon can be called a supermoon even if it is or close (within 90%) to perigee. Sometimes, perigee and full moon line up within a few hours or even a day or more apart.
The December 4 supermoon, for example, will be fully lit about 12 hours after reaching perigee. As a result, it will be the second-biggest and brightest supermoon of the year after the one in November.
Viewing the Cold Supermoon
For the best viewing experience, step outside shortly after sunset and look toward east. The supermoon will rise just above the horizon as a huge golden orb with unusually high brightness. Estimates suggest it will be nearly 8% larger than an average full Moon and up to 17% brighter. The difference will be noticeable to the naked eye, especially when the Moon is low on the horizon.
The Jupiter-Moon conjunction
A few days after the supermoon event, the Moon will meet up with Jupiter in the night sky. NASA says the two will meet during a conjunction on the evening of December 7 in the eastern sky.
During a conjunction, two objects seem to be separated by just a few degrees from our perspective when they are actually hundreds of millions of kilometres apart. To witness the rare event, look up east around 11 pm where Jupiter will shine like a bright dot just above the Moon.
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