Is the Full Moon seen the same everywhere on the same date?


Astronomers define when a Full Moon occurs by its phase as seen at the so-called Standard Meridian on Earth which passes through Greenwich England. All predictions and forecasts are based on planetary positions and celestial events on this time standard. As you know, traveling west of Greenwich puts you into time zones that are earlier in time than Greenwich Standard Time and 'Universal Time' by an amount that depends on your longitude at the rate of 1 hour earlier for every 15 degrees of longitude and fractions thereof.

If Full Moon is reported to occur at 3 hours Universal Time by the calculations, a lucky bloke living in England will see it at 3:00 AM, but someone in New York will have seen it the previous day at 10:00 PM because of the 5 hour time zone difference. So, Full Moons do not have to occur on the same calendar date, but will occur on the same evening over the Earth. You just have to know what it's universal time will be, and know what your current universal time is to anticipate it.

Return to Dr. Odenwald's FAQ page at the Astronomy Cafe Blog.