Once in a Blue Moon

The Double Blue Moon of 2018

Our Blue Moon Calculator says that in 2018, there is a double Blue Moon: both January and March have two Full Moons. This is true for most of the world, but not New Zealand, whilst in eastern Australia, things get a bit complicated.

Let's start with the basic astronomical facts. The Full Moons for January 2018 to April 2018 are as follows:

2 January 2018 at 02:24 UTC
31 January 2018 at 13:26 UTC
2 March 2018 at 00:51 UTC
31 March 2018 at 12:37 UTC
30 April 2018 at 00:58 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.

Here are those five 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 Full Moon 3 Full Moon 4 Full Moon 5
Places East of Greenwich
Auckland UTC + 12 hours Jan 2
15:24¹
Feb 1
02:26¹
Mar 2
13:51¹
Apr 1
01:37¹
Apr 30
12:58
Sydney UTC + 10 hours Jan 2
13:24¹
Feb 1
00:26¹
Mar 2
11:51¹
Mar 31
23:37¹
Apr 30
10:58
Brisbane UTC + 10 hours Jan 2
12:24
Jan 31
23:26
Mar 2
10:51
Mar 31
22:37
Apr 30
10:58
Adelaide UTC + 9 hours 30 minutes Jan 2
12:54¹
Jan 31
23:56¹
Mar 2
11:21¹
Mar 31
23:07¹
Apr 30
10:28
Tokyo UTC + 9 hours Jan 2
11:24
Jan 31
22:26
Mar 2
09:51
Mar 31
21:37
Apr 30
09:58
Perth UTC + 8 hours Jan 2
10:24
Jan 31
21:26
Mar 2
08:51
Mar 31
20:37
Apr 30
08:58
Kolkata UTC + 5 hours 30 minutes Jan 2
07:54
Jan 31
18:56
Mar 2
06:21
Mar 31
18:07
Apr 30
06:28
Karachi UTC + 5 hours Jan 2
07:24
Jan 31
18:26
Mar 2
05:51
Mar 31
17:37
Apr 30
05:58
Moscow UTC + 3 hours Jan 2
05:24
Jan 31
16:26
Mar 2
03:51
Mar 31
15:37
Apr 30
03:58
Johannesburg UTC + 2 hours Jan 2
04:24
Jan 31
15:26
Mar 2
02:51
Mar 31
14:37
Apr 30
02:58
Paris UTC + 1 hours Jan 2
03:24
Jan 31
14:26
Mar 2
01:51
Mar 31
14:37¹
Apr 30
02:58¹
The Greenwich Meridian
London UTC Jan 2
02:24
Jan 31
13:26
Mar 2
00:51
Mar 31
13:37¹
Apr 30
01:58¹
Places West of Greenwich
Sao Paulo UTC - 3 hours Jan 2
00:24¹
Jan 31
11:26¹
Mar 1
21:51
Mar 31
09:37
Apr 29
21:58
Halifax UTC - 4 hours Jan 1
22:24
Jan 31
09:26
Mar 1
20:51
Mar 31
09:37¹
Apr 29
21:58¹
New York UTC - 5 hours Jan 1
21:24
Jan 31
08:26
Mar 1
19:51
Mar 31
08:37¹
Apr 29
20:58¹
Chicago UTC - 6 hours Jan 1
20:24
Jan 31
07:26
Mar 1
18:51
Mar 31
07:37¹
Apr 29
19:58¹
Edmonton UTC - 7 hours Jan 1
19:24
Jan 31
06:26
Mar 1
17:51
Mar 31
06:37¹
Apr 29
18:58¹
Los Angeles UTC - 8 hours Jan 1
18:24
Jan 31
05:26
Mar 1
16:51
Mar 31
05:37¹
Apr 29
17:58¹
Hawaii UTC - 10 hours Jan 1
16:24
Jan 31
03:26
Mar 1
14:51
Mar 31
02:37
Apr 29
14:58
¹ Daylight saving time is in effect.

As you can see, Europe, Africa, the Americas and Asia have a Double Blue Moon in 2018. So does western and central Australia, as well as the state of Queensland in eastern Australia and the town of Broken Hill in New South Wales.

However, eastern Australia (except Queensland and Broken Hill) and New Zealand have only one Blue Moon. It falls in March in eastern Australia (except Queensland and Broken Hill) and in April in New Zealand. This happens because the Full Moons which the rest of the world sees on January 31 and March 31 are shifted to the following month in time zones that are 11 or more hours ahead of UTC.

What is special about Queensland? It doesn't observe daylight saving time, so it is only 10 hours ahead of UTC whilst the other states of eastern Australia are 11 hours ahead.

And Broken Hill, a mining town in western new South Wales, keeps the same time as South Australia, so it is 10.5 hours ahead of UTC in summer and 9.5 hours ahead during the rest of the year.