(meteorobs) Semi OT- Change of Astronomical Time

Richard Taibi rjtaibi at hotmail.com
Thu Jan 26 11:26:32 EST 2012

Several months ago someone on the list asked (as I remember) when the time convention that astronomers used changed.  Before the change, astronomers, like Charles P. Olivier (founder of the American Meteor Soc'y) for one, 'began' their observational day at noon.  So, in that scheme, 1 p.m.= 1 h, 1 a.m.=13h, 2 a.m.=14h, and so on, until the next 12 noon, when the following observing day began.  Those of you familiar with Olivier's meteor rate catalogs are familiar with this system because he used the system for what we now would term the 'early morning hours.'  The virtue of the system, it was argued, was that the issue of which 'day' the observation occurred on was simplified, because the numeration was continuous over the night-time hours.
This all changed on January 1, 1925 after an international dialog about changing the system had been conducted.  So, long story short, time 'changed' on Jan. 1, 1925!  Now, we use 'January 26/27', for tonight for example, to specify the night we are specifying.  
I hope this is still of some interest.  You can read an astronomer's discussion of the issue at: http://adsabs.harvard.edu/article_service.html.  Once you are at this site, click on 'Scanned journals service'.  At the next page, click on Popular Astronomy and enter volume 33, page 1 in the appropriate places. Best wishes,  Rich

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