New moons on calendars?

Calendars intended for use in the U.S. will typically vary as follows:

1) They may use any of the four major U.S. time zones -- Eastern, Central, Mountain, or Pacific. I think Eastern and Central zones are both widely used.

2) They may or may not properly reflect Daylight Saving Time. The ones I've looked at so far ignore daylight time.

Some calendars are forthcoming about their time zone, but others are not.

example #1:

Sierra Club Engagement Calendar 2009

This says, "Astronomical information is given in Eastern Standard Time", and that's what it does.

example #2:

Bay Area 2009 Tide Calendar (for northern California)

This calendar doesn't specify the time zone, so I have to figure out what it's doing by studying it. The tide and sunrise/sunset information are given in local time (Pacific Standard or Daylight, whichever is in effect). On the other hand, moon-phase dates are in Pacific Standard Time (with no correction for daylight time).

example #3:

A calendar I received from a real-estate agent says, "All dates are given in terms of Central Standard Time." (For instance, there's a first-quarter moon on 10/26/2009 at 12:42 AM EST, but the calendar shows a date of 10/25.)

I doubt that many U.S. calendars base the dates on Universal Time, but there might be some.

bottom line:

Calendars are pretty loose about this, and there is no standard. If you want accurate times for moon phases, you should look at a reliable reference such as the following site:

http://aa.usno.navy.mil/data/docs/MoonPhase.php

Even if a calendar uses Eastern Standard time, it will never deviate from the major U.S. time zones by more than 3 hours. If a moon phase occurs at 2 AM EST, it would be difficult to tell by looking at the moon whether the phase really occurred on that day or the previous day; so from a practical viewpoint, it doesn't really matter.

On most U.S. printed calenders, they will use Eastern Standard Time. International ones will use UT.

Just eyeballing January 2009:

Full Moon Jan. 10 @ 10:27P.M. EST... (This would appear as January 11 on your calender if it were based on UT)

New Moon Jan 26 @ 2:55A.M. EST (This moment would be on January 25 if you were in the Pacific Time Zone)

Although it does seem a little eerire that you can visually detect the New Moon being "off by a day or more" from what your sources say.

Hi Janet,

Dr. Bob, and Dave M have the right idea. Since phases of the moon are determined by the Prime Meridian, located in Greenwich, London, the moon phases are based on Universal (or Greenwich) Time. That said, it is five hours ahead of EST. So, it will depend on three basic factors:

1) Your time zone, 2) Where your calendar is printed, 3) What is the time of the new moon in UT.

Suffice it to say, regardless, you can do your own calculations, if it is important to you, and try adding a moon phase calculator to your google toolbar. You can locate it at:

http://www.google.com/ig/adde?moduleurl=www.calcul...

Hope this helps!

I think that depends on the particular printer or manufacturer. When people ask for dates here I usually post UT dates, and maybe convert to local time if I know where the questioner is located, or Eastern Time (where I'm located).

There's only one moon. We all get to share it.