Today, October 17, marks the appearance of the “supermoon” in the night sky, offering the public a chance to witness the largest and closest full moon of the year.
At 7:26 PM, the moon will reach its full phase, known in astronomical terms as “opposition.” Engineer Wang Kechao from the Purple Mountain Observatory of the Chinese Academy of Sciences explains, “In astronomy, we define the moment when the moon appears the roundest as ‘opposition.’ This refers to the moon and the sun having a difference of 180 degrees in their geocentric longitude. At this time, the moon, Earth, and sun are nearly aligned in a straight line, making the moon appear its fullest.”
Astronomy experts note that the moon’s orbit around the Earth is slightly elliptical. The point at which the moon is closest to Earth is called perigee, approximately 360,000 kilometers away, while the farthest point is apogee, about 400,000 kilometers away. This variation in distance causes us to perceive differences in the moon’s size. Therefore, when a full moon occurs close to perigee, it appears larger and brighter, qualifying it as a “supermoon.”
Notably, just ten hours before the moon reaches its “opposition” at 7:26 PM, it will pass through perigee at 8:51 AM, making this year’s full moon moment the closest one to the perigee occurrence. As a result, this full moon is not only the largest of the year but also a “supermoon.”
It’s important to highlight that supermoons are not rare events. Experts say that they can occur one to four times a year. In fact, there are a total of four supermoons this year, with the last one occurring on November 16. So, even if you miss today’s supermoon, there will be plenty of opportunities to catch the next ones.
Observing a supermoon is relatively straightforward. When the moon rises just above the eastern horizon, it appears larger and rounder against ground references and may exhibit a slight reddish hue. As it ascends higher in the sky, the color gradually changes to white or off-white. For astronomy enthusiasts, using a small telescope can enhance the view of the moon’s surface details, or you can capture stunning photographs to create your own masterpiece of the supermoon.
