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Re: Is VMA Wrong?

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  • jimmosher
    Travis, Yes, it looks like VMA is telling you the time of the Moon s phases in your current local time, Central Daylight Savings Time (CDT), which I believe
    Message 1 of 12 , Aug 1, 2010
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      Travis,

      Yes, it looks like VMA is telling you the time of the Moon's phases in your current local time, "Central Daylight Savings Time" (CDT), which I believe is obtained by subtracting 5 hours from UT (including changing the date as required by the subtraction). To go the other way, you add 5 hours. So 22:08 (or "10:08 pm") CDT on August 9, 2010 is completely consistent with 03:08 UT on August 10, 2010, the official moment of New Moon. They signify the same instant.

      Yes, your moonset is at around 19:37 CDT, at which local time the Moon is just below your western horizon and the Sun slightly over 4° above it (making the Moon impossible to see, even if it weren't hidden by the horizon).

      And yes, your moonset is about 2-1/2 hours before the official moment of New Moon mentioned above. But the conclusion that VMA is saying the New Moon in some sense "occurs" 2-1/2 hours west of your location is not really valid, or perhaps I don't understand what you mean by that. If one stayed at your latitude but moved 2-1/2 time zones west, to a point in the ocean a bit west of Oregon at a longitude of 125.5° west (each hour-wide time zone spanning 15° in longitude), and looked 2-1/2 hours later (at the official moment of New Moon), one would essentially be chasing the movement of the Moon, and what one would see would again be the Moon setting on the western horizon, but this time with the Sun even closer to it and (this month) a bit to the Moon's north. So you could indeed see the Moon at its moment of "Newness" from that location, but it would be very low.

      As previously indicated, the place on Earth where you would have to stand to see the Moon (and Sun) directly overhead at 2010 Aug 10 03:08 UT (the official moment of "New Moon") is in the ocean east of the Philippines (near 133.4°E, 12.9°N, to be precise). Whether that means the New Moon "occurs" there, any more than it "occurs" in the water off Oregon, is a matter of taste. To my taste the New Moon is something that "occurs" at a specific time (2010 Aug 10 03:08 UT, in this case) but not at any particular place.

      -- Jim


      --- "Travis" <travisedwin@...> wrote:

      > Jim--

      > Thanks again for your observations.

      > I'm not sure of what, exactly, VMA is trying to tell me. But
      > now that you've mentioned the time, I find VMA says the new
      > moon will occur at 22:08 (this is Chicago, IL, approximately
      > 42 degrees north and 88 degrees west). I assume this is local
      > time.

      > The moon sets at 19h37m on Aug. 9, so the new moon occurs
      > about 2-1/2 hours after moon set. So the new moon will occur
      > about 2-1/2 hours west of Chicago, according to VMA.

      > I don't think this should affect the date. But, just as a
      > final note, this morning's Chicago Tribune identified
      > August's new moon as occuring on August 9!

      > Oh well!

      > Travis
    • OldWolf
      The newspapers never use UT (unless your in the UK and the Clocks have gone back to GMT!) they are always on local time Nick
      Message 2 of 12 , Aug 2, 2010
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        The newspapers never use UT (unless your in the UK and the Clocks have gone back to GMT!) they are always on local time

        Nick

        --- In lunar-observing@yahoogroups.com, "Travis" <travisedwin@...> wrote:
        >
        > Jim--
        >
        > Thanks again for your observations.
        >
        > I'm not sure of what, exactly, VMA is trying to tell me. But now that you've mentioned the time, I find VMA says the new moon will occur at 22:08 (this is Chicago, IL, approximately 42 degrees north and 88 degrees west). I assume this is local time.
        >
        > The moon sets at 19h37m on Aug. 9, so the new moon occurs about 2-1/2 hours after moon set. So the new moon will occur about 2-1/2 hours west of Chicago, according to VMA.
        >
        > I don't think this should affect the date. But, just as a final note, this morning's Chicago Tribune identified August's new moon as occuring on August 9!
        >
        > Oh well!
        >
        > Travis
        >
        >
        > --- In lunar-observing@yahoogroups.com, Jim Mosher <jimmosher@> wrote:
        > >
        > > --- In lunar-observing@yahoogroups.com, "Travis" <travisedwin@> wrote:
        > >
        > > > When I go to the "Date/Time" screen in my VMA I can uncheck the
        > > > "Use computer date and time" box, but when I do there's no way to
        > > > adjust the hours offset. My copy continues to say "Country: United
        > > > States, Time Zone: America/Chicago."
        > >
        > > Sorry about the confusion! I wrote the earlier reply based on my mental recollection of VMA (I normally use Version 4), and their on-line documentation, without having access to a computer on which I could run VMA at the time.
        > >
        > > > I have VMA Ver. 5.5, if that affects anything.
        > > > I didn't note in my original post that my confusion was caused by
        > > > the fact that all of VMAs other new moon dates seem to be correct.
        > > > Only the August date is wrong.
        > >
        > > I'm not familiar with VMA Ver. 5.5, but I'm attaching a screenshot of Ver. 5.0. The left panel shows (at "1") how you use the "Configuration" menu to set VMA to operate in Universal Time (called "GMT" there). When this is done the "Ephemeris" display gives (at "2") the same UT information as the USNO for the upcoming New Moon (geocentric conjunction). Before taking the screenshot, the "Now" button had been pressed, which gives the information show at lower left. In particular, you can see how your local time is converted to Ephemeris Time ("TT", close to UT) at "3". Everything above "3" (including the New Moon display) lists *local* dates and times, which will change depending on your time zone setting at "1".
        > >
        > > It's possible that Ver. 5.5 works differently, or has a programming flaw, but it is perhaps important to emphasize again that "New Moon" in the astronomical sense means a precisely defined, but somewhat arbitrarily moment in time. A consequence of the definition as "the moment of geocentric conjunction" is that not all observers' local calendars will give the same date, nor will their watches give the same time.
        > >
        > > In this particular case, "New Moon" describes the state of affairs at 2010 Aug 10 03:08 UT. According to LTVT the Moon will be over a point in the Pacific Ocean a little east of the Philippines. It will be visible, at that instant, from half the world, including Honolulu, Hawaii, where I believe local clocks will read "5:08 pm on Aug. 9, 2010" (UT - 10 h), and from Tokyo, Japan where (at the same instant) they will read "12:08 pm on Aug. 10, 2010" (UT + 9 h). In Greenwich, UK the Moon will not be visible but the clocks will read "4:08 am on Aug. 10, 2010" (UT + 1 h due to "British Summer Time"). Note that the local date is different in Hawaii from what it is in Japan or the UK.
        > >
        > > This is not atypical: at *any* instant of time (such as the moment of most any astronomical phenomenon) there are going to be places on Earth where the date shown on local calendars differs by one day. As a result it is impossible for calendar makers to correctly assign Moon phase symbols to specific dates without knowing the locality where they will be used.
        > >
        > > Since in your postings you express concern about the date but not the time, perhaps this is the root of the problem you are referring to?
        > >
        > > -- Jim
        > >
        > >
        > >
        > >
        > >
        > > --
        > >
        >
      • Travis
        Nick and Jim-- Thanks for your thoughts. When I originally posted here I didn t realize there is a VMA site It s here:
        Message 3 of 12 , Aug 2, 2010
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          Nick and Jim--

          Thanks for your thoughts.

          When I originally posted here I didn't realize there is a VMA site' It's here:

          http://tech.groups.yahoo.com/group/virtualmoon/

          When I found out the group existed I posted my question there and Patrick Chevalley sent this answer:

          "It depend the time zone you use.
          The new moon is August 10 3h08 GMT.
          This is August 9 22h08 local time for you.

          "VMA show your local time if you set your time in Configuration/General menu.
          Check "Use computer date"
          Select "United States" for Country and "America/Chicago" for Time zone.

          "Patrick"

          This cleared things up and agrees with the answers the people here provided.

          Thanks again all.

          Travis



          --- In lunar-observing@yahoogroups.com, "Travis" <travisedwin@...> wrote:
          >
          > Jim--
          >
          > Thanks again for your observations.
          >
          > I'm not sure of what, exactly, VMA is trying to tell me. But now that you've mentioned the time, I find VMA says the new moon will occur at 22:08 (this is Chicago, IL, approximately 42 degrees north and 88 degrees west). I assume this is local time.
          >
          > The moon sets at 19h37m on Aug. 9, so the new moon occurs about 2-1/2 hours after moon set. So the new moon will occur about 2-1/2 hours west of Chicago, according to VMA.
          >
          > I don't think this should affect the date. But, just as a final note, this morning's Chicago Tribune identified August's new moon as occuring on August 9!
          >
          > Oh well!
          >
          > Travis
          >
          >
          > --- In lunar-observing@yahoogroups.com, Jim Mosher <jimmosher@> wrote:
          > >
          > > --- In lunar-observing@yahoogroups.com, "Travis" <travisedwin@> wrote:
          > >
          > > > When I go to the "Date/Time" screen in my VMA I can uncheck the
          > > > "Use computer date and time" box, but when I do there's no way to
          > > > adjust the hours offset. My copy continues to say "Country: United
          > > > States, Time Zone: America/Chicago."
          > >
          > > Sorry about the confusion! I wrote the earlier reply based on my mental recollection of VMA (I normally use Version 4), and their on-line documentation, without having access to a computer on which I could run VMA at the time.
          > >
          > > > I have VMA Ver. 5.5, if that affects anything.
          > > > I didn't note in my original post that my confusion was caused by
          > > > the fact that all of VMAs other new moon dates seem to be correct.
          > > > Only the August date is wrong.
          > >
          > > I'm not familiar with VMA Ver. 5.5, but I'm attaching a screenshot of Ver. 5.0. The left panel shows (at "1") how you use the "Configuration" menu to set VMA to operate in Universal Time (called "GMT" there). When this is done the "Ephemeris" display gives (at "2") the same UT information as the USNO for the upcoming New Moon (geocentric conjunction). Before taking the screenshot, the "Now" button had been pressed, which gives the information show at lower left. In particular, you can see how your local time is converted to Ephemeris Time ("TT", close to UT) at "3". Everything above "3" (including the New Moon display) lists *local* dates and times, which will change depending on your time zone setting at "1".
          > >
          > > It's possible that Ver. 5.5 works differently, or has a programming flaw, but it is perhaps important to emphasize again that "New Moon" in the astronomical sense means a precisely defined, but somewhat arbitrarily moment in time. A consequence of the definition as "the moment of geocentric conjunction" is that not all observers' local calendars will give the same date, nor will their watches give the same time.
          > >
          > > In this particular case, "New Moon" describes the state of affairs at 2010 Aug 10 03:08 UT. According to LTVT the Moon will be over a point in the Pacific Ocean a little east of the Philippines. It will be visible, at that instant, from half the world, including Honolulu, Hawaii, where I believe local clocks will read "5:08 pm on Aug. 9, 2010" (UT - 10 h), and from Tokyo, Japan where (at the same instant) they will read "12:08 pm on Aug. 10, 2010" (UT + 9 h). In Greenwich, UK the Moon will not be visible but the clocks will read "4:08 am on Aug. 10, 2010" (UT + 1 h due to "British Summer Time"). Note that the local date is different in Hawaii from what it is in Japan or the UK.
          > >
          > > This is not atypical: at *any* instant of time (such as the moment of most any astronomical phenomenon) there are going to be places on Earth where the date shown on local calendars differs by one day. As a result it is impossible for calendar makers to correctly assign Moon phase symbols to specific dates without knowing the locality where they will be used.
          > >
          > > Since in your postings you express concern about the date but not the time, perhaps this is the root of the problem you are referring to?
          > >
          > > -- Jim
          > >
          > >
          > >
          > >
          > >
          > > --
          > >
          >
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