Astronomically speaking, it’s just 2451544.5 in the Julian Day reckoning. As I write this on Thanksgiving Day (the 25th of November = JD 2451507.5), there are 37 days left to the Y2K celebrations. That’s one good reason why astronomers use Julian days in their calculations: differences in time are quite easily found by subtracting Julian dates. The start of the Julian calendar, from the beginning of the year –4712 (or 4713 B.C., but more on this later), was deliberately set so long ago that any reasonable date would always be positive. The reason for the “.5” or half day is equally practical: by tradition the Julian day starts at Greenwich noon, meaning that all events of a given night happen on the same numerical date. At least that’s the way it works for European observers.

The Y2K date of most astronomical significance is 1.5 Jan 2000 or rather 2451545.0. This is J 2000.0, the epoch for current star charts, positions, orbital elements and ephemerides. Here too, the decimals have meaning, the “.0” signifying the beginning of the year. Because of precession, the wobbling of the Earth’s axis (currently near Polaris) about the pole of the ecliptic once in about 26,000 years as well as some other minor effects, the right ascension and declination—celestial longitudes and latitudes—of even the fixed stars are constantly changing. Slowly, but they are changing. The positions marked in your J2000.0 star atlas are strictly correct only for 1.5 January, or 7 am EST.

My old copy of Norton’s Star Atlas shows 1950.0 coordinates, while the newer Bright Star Atlas is in 2000.0. There is little change over most of the celestial sphere, but in some familiar places like the Big Dipper there are noticeable differences. The line of 11 h in R.A. has now shifted fully west (right) of the Pointer stars Dubhe and Beta. But much more than the Roman numerals of R.A. have changed. Numerous double stars are indicated with sigma, and all other deep sky objects are a uniform pattern of dots. Messier objects are labeled with the M after the number, and cryptic Herschel codes are used rather than the NGC numbers more familiar today. Successive charts reflect not only slow wobble of the planet, but also the much more rapid changes in amateur astronomy over the last half century. With new atlases so detailed and massive, best shelved on a CD-ROM, I wonder if the epoch 2000.0 charts will be the last printed and bound.

Who will see 2000 first? Geography gives New Zealand the honor as the first populated country just west of the Date Line. Plus, New Zealand is on daylight time, 13 h ahead of Greenwich, 18 h ahead of Eastern Time. This means the party can get going yet an hour earlier. Y2K problems? No worries. It's early summer, and New Zealanders will do what they would ordinarily do on any holiday: go to the beach!

And the first sunrise of the new year? Assuming clear skies, the Sun will rise just after 5 am in the Chatham, Pitt and Antipodes Islands. The first sunrise on the North Island will be seen from the 1752 m summit of Mt. Hikurangi at 5:40, followed seven minutes later by dawn at Gisborne, the first city to be illuminated in the new year. Needless to say, celebrations, concerts, fireworks and hakas are just some of the planned events.

Popular culture and the media are convinced that we’re about to enter a new millennium. Kevin the Cockroach is New Zealand's symbol of Y2K preparedness. Channel 3 is the “Official Millennium Broadcaster” (whatever that is...), while Air New Zealand will be flying “from one millennium to the next,” most reassuring for those aboard their flights! Denys the Little in the 6th century got it wrong and skipped counting the Year 0, following 1 B.C. with 1 A.D. Two thousand years later, we still debate whether the third millennium begins in 2000 or 2001. But revelers and corporate sponsors surely don’t want to chance being left out. Think of this New Year as a trial run, Y2K bugs and all. Since 1 January 2001 is JD 2451910.5, we have only 403 days to go to the next millennium!

With holiday wishes for clear skies in the New Year,
Moondark is written by Doug Miller and published on the web, in the Delmarva Star Gazers' Star Gazer News and in the Delaware Astronomical Society's FOCUS. Please address comments and suggestions to dmiller@udel.edu. This document was last revised on 26 November '99. All text and images copyright © 1999 Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.