The Blue Moon of 2004

Our Blue Moon Calculator says that in 2004, there is a Blue Moon in July. You may have heard or read reports which said that the Blue Moon really occurs in August. Who is right?

Well, you could see Blue Moons in both months, but it depends where in the world you live.

Let's start with the basic astronomical facts. The three Full Moons in July and August 2004 are as follows:

2 July	at	11:09 GMT
31 July	at	18:05 GMT
30 August	at	02:22 GMT

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 Greenwich Mean Time (GMT) which is the standard time zone used by astronomers worldwide.

Notice that the second Full Moon in the list occurs less than six hours before the end of 31 July. Changing the time zone by six hours or more to the east of Greenwich changes the month in which the Full Moon falls. In Australia, New Zealand and the Far East, the Full Moon is on 1 August, not 31 July.

Here are those three 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 fell in the same calendar month are highlighted.

City	Time zone	Full Moon 1	Full Moon 2	Full Moon 3
Places East of Greenwich
Sydney	GMT + 10 hours	Jul. 2 21:09	Aug. 1 04:05	Aug. 30 12:22
Tokyo	GMT + 9 hours	Jul. 2 20:09	Aug. 1 03:05	Aug. 30 11:22
Islamabad (Pakistan)	GMT + 5 hours	Jul. 2 16:09	Jul. 31 23:05	Aug. 30 07:22
Moscow¹	GMT + 4 hours	Jul. 2 15:09	Jul. 31 22:05	Aug. 30 06:22
The Greenwich Meridian
London¹	GMT + 1 hour	Jul. 2 12:09	Jul. 31 19:05	Aug. 30 03:22
Places West of Greenwich
New York¹	GMT - 4 hours	Jul. 2 07:09	Jul. 31 14:05	Aug. 29 22:22
Chicago¹	GMT - 5 hours	Jul. 2 06:09	Jul. 31 13:05	Aug. 29 21:22
Los Angeles¹	GMT - 7 hours	Jul. 2 04:09	Jul. 31 11:05	Aug. 29 19:22
Hawaii	GMT - 10 hours	Jul. 2 01:09	Jul. 31 08:05	Aug. 29 16:22
¹ These places observe daylight saving time in July and August.

As you can see, Australia, New Zealand and the Far East see two Full Moons in August, whilst the rest of the world sees two Full Moons in July instead.

Obliquity is proud to be a partner with Hawthorn Press in the creation of The Stargazers' Almanac 2008, your monthly guide to the stars and planets.

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