SKYLIGHTS
Astronomy news for the week starting Friday, December 31, 1999.
Skylight's week begins on December 31, 1999, a momentous date
indeed, the last date of the 1990s, the pin on which turns the
beginning of the new millennium. Or not, depending on how you feel
about when the millennium actually begins. Technically, as has
been cited so many times, the millennium does not actually start
until 2001. But who is counting? The new round number is
impressive indeed, and whether 2000 is the last year of the second
millennium or the first of the third (and hardly in all
calendars!), it is a fine year to contemplate. So Happy New Year
to all, with wishes for a fine 2000.
The year 2000 is also highly unusual in that it is a leap year. To
keep our common Gregorian calendar pinned to the equinoxes and
solstices, we skip leap years in century years NOT divisible by
400. The year 1900 was not a leap year, nor will 2100, 2200, or
2300 be leap years, but 2000 will. This system produces a long-
term average of 365.2425 days per year, preciously close to the
actual value of 364.2422... days.
We begin 2000 with the Moon in its waning crescent phase heading
for new, the Moon passing more or less between us and the Sun (no
eclipse) on Thursday, January 6. Two days before, on Tuesday the
4th, the Moon passes its apogee. While the perigean Moon produced
especially high tides during the last full phase in December, the
apogean Moon will make especially small-scale tides. Before
reaching the Sun, the Moon will pass to the north of Venus the
night of Sunday the 2nd, appearing to the northeast of the planet
the morning of Monday the 3rd. The same day it will occult, or
pass over, the asteroid Vesta, the event not visible in North
America.
The night of Sunday, January 2, marks a special time of year, the
date (this year) when the Earth passes its perihelion, its closest
point to the Sun, at a distance of 147,102,790 km (91,405,436
miles), 1.70 percent closer than average. At this moment, Earth
globally receives the greatest solar heat. Given that perihelion
occurs during the dead of northern winter, the solar distance
clearly has little effect on the seasons (the sole cause of which
is the 23.5 degree tilt of the Earth's rotation axis). The most
noticeable effect is that at perihelion, the Earth moves faster in
its elliptical orbit, the result a shortening of winter, which is
four days shorter than northern summer.
Jupiter and Saturn are now high to the south at 7 PM. By 11 PM
they have shifted to the west, their glory replaced by Orion and
its crew. Keep your eye out too for the Quadrantids the morning of
Tuesday, January 4th. One of the best meteor showers of the year,
the Quadrantids -- named after Quadrans, a defunct constellation
near the Big Dipper -- can produce 100 meteors per minute. Only
cold skies keep it from being as well known as August's Perseids.
