Once in a Blue Moon

The Blue Moon of 2023

Our Blue Moon Calculator says that in 2023, there is a Blue Moon in August. Is that true in all parts of the world? After all, previous Blue Moons have fallen on different days in different parts of the world.

Let's start with the basic astronomical facts. The Full Moons for August 2023 are as follows:

1 August at 18:31 UTC
31 August at 01:35 UTC

These dates and times have been calculated rigorously using the same methods as those employed by the United States Naval Observatory and by Her Majesty's Nautical Almanac Office. They are given in Coordinated Universal Time (UTC) which is the standard time zone used by astronomers worldwide. It is effectively the same as Greenwich Mean Time (GMT).

Here are those Full Moons again, but with the dates and times adjusted for several major time zones around the world. For each time zone, the two Full Moons which fall in the same calendar month are highlighted.

City Standard Time Zone Full Moon 1 Full Moon 2
Auckland UTC + 12 hours Aug 2
06:31		 Aug 31
13:35
Sydney UTC + 10 hours Aug 2
04:31		 Aug 31
11:35
Adelaide UTC + 9 hours 30 minutes Aug 2
04:01		 Aug 31
11:05
Brisbane UTC + 10 hours Aug 2
04:31		 Aug 31
11:35
Perth UTC + 8 hours Aug 2
02:31		 Aug 31
09:35
Tokyo UTC + 9 hours Aug 2
03:31		 Aug 31
10:35
Shanghai UTC + 8 hours Aug 2
02:31		 Aug 31
09:35
Kolkata UTC + 5 hours 30 minutes Aug 2
00:01		 Aug 31
07:05
Karachi UTC + 5 hours Aug 1
23:31		 Aug 31
06:35
Moscow UTC + 3 hours Aug 1
21:31		 Aug 31
04:35
Johannesburg UTC + 2 hours Aug 1
20:31		 Aug 31
03:35
Paris UTC + 1 hours Aug 1
20:31¹		 Aug 31
03:35¹
London UTC Aug 1
19:31¹		 Aug 31
02:35¹
Sao Paulo UTC - 3 hours Aug 1
15:31		 Aug 30
22:35
Halifax UTC - 4 hours Aug 1
15:31¹		 Aug 30
22:35¹
New York UTC - 5 hours Aug 1
14:31¹		 Aug 30
21:35¹
Chicago UTC - 6 hours Aug 1
13:31¹		 Aug 30
20:35¹
Edmonton UTC - 7 hours Aug 1
12:31¹		 Aug 30
19:35¹
Los Angeles UTC - 8 hours Aug 1
11:31¹		 Aug 30
18:35¹
Hawaii UTC - 10 hours Aug 1
08:31		 Aug 30
15:35
¹ Daylight saving time is in effect.

As you can see, most of the world has a Blue Moon on 31 August. The exceptions are the Americas and eastern Pacific. Their time zones are sufficiently far behind GMT that the second Full Moon occurs in the afternoon or evening of 30 August instead.

Once in a Blue Moon Who wrote this?

Copyright © 2023 by David Harper and L.M. Stockman
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