At 05:33 PM 8/14/96 -0500, you wrote: >I am a sundial enthusiast an have been an on-looker of this list for somew >time. Now I need some help from all of you. I am planning on getting >married in september of 97. I hope to get married on the equinox >(autumnal) I would like to know the exact time of the equinox given in US >Central time zone. Also, I wonder what is the tolerence for the equinox. >i.e. can the whole day be considered as the equinox or even three days, >one before and one after? > >My point is that if the equinox happens on a tuesday and we want to get >married on a sunday can we call it the equinox? > >hope to hear from many of you > >bart >
Hi Bart First congratualtions to you and your fiancee on the decision to marry and congratulations on the decision to tie your personal event with the astronomical event. Now the answer: In 1997 the autumnal equinox will occur on Monday, Sep 22 at 2348 GMT You asked for the time in US Central and this is 1748 but since in September the daylight time is in use in your zone this will be 1848 US Central Daylight Time. Now some explanations: 1. The moment of equinox is the time when the center of the solar disk crosses the Celestial Equator which is the projection of the Earth equator on the Celestial Sphere. This is precisely one instant of time for everyone on the Earth but how it relates to your date and local time depends on your longitude. 2. This year, 1996, the autumnal equinox occurs on Sunday Sep 22 at 1800 GMT (1200 US Central, 1300 US Central Daylight) so if you moved your marriage to this year it would be exactly on the very equinox day. 3. Tolerance. The tolerance depends on the accuracy you need. In the Central Time zone the Sun on Sunday Sep 21, 1997 won't even start grazing the equator which could be considered the starting of the equinox. The process from the monent when the Sun touches the Celestial Equator till it leaves it altogether takes more than 32 hours. The equinox, as mentioned earlier is the moment when the Sun's center reaches the Equator. So unfortunately Sun, Sep 21 1997 is not going to be the equinox day. 4. I think that you can easily marry on Sunday even if it is not exactly the equinox day (making it on Monday would be impractical). If you really want to marry on Sunday that is the day of the equinox do it either this year (one year earlier or later does not make much difference if you plan your marriage for life) or do it in 1997 but on Hawaii. Hawaii is 10 hours slow on GMT so the exact equinox in 1997 in Hawaii will occur Mon Sep 22 at 1348 Hawaiian time (they do not use daylight saving time) which is still Monday but the process of "equinoxing" shall start on Sun, Sep 21 at about 2126 Hawaiian time (again this is the time when the solar disk touches the equator). This may be considered as a demonstration of relation (non-relativistic) between space and time. You either marry this year at home or do it next year but on Hawaii. 5. I took my data from the Nautical Almanach 1996 issued by her Majesties Nautical Almanach Office, London, England. Nautical Almanachs give methods for using them for the following year for the Sun and stars (sometimes it may be hard to get the new almanach when at sea). You may try to reach professional astronomers but this may be hard. 6. Someone on the Sundials mailing list, please check my calculations and consideration. After all marriage is very important matter. Sincerely - Slawek Grzechnik
