Photo of the Week. Remembering blue skies and
autumn's trees.
Astronomy news for the week starting Friday, February 29, 2008.
It's a first for Skylights, to be starting the week on the day that
marks our
leap year, February 29. The purpose of the leap year is to
make the year's average length come out to 365 1/4 days over a four
year period, which closely matches the actual length of 365.2422...
days. The small difference is taken care of in our Gregorian
Calendar by dropping leap years in century years not divisible by
400, giving an average year-length over 400 years of 365.2425 days,
almost perfect, the error but one day in 3000 years.
And the week rather oddly finds the
Moon entirely within the waning
crescent phase, as last quarter was
passed on Thursday the 28th, and new Moon will not be hit until
Friday, March 7. The mornings of Sunday the 2nd and Monday the
3rd, the Moon will make nice pairings with
Jupiter, first to the southwest of the giant planet and then to
the southeast of it. The following morning, that of Tuesday the
4th, the Moon will lie between Jupiter and the close pairing of Venus and Mercury,
which will both at best be just above the southeastern dawn horizon
and be quite difficult to see. The Moon then not only passes Venus
and Mercury on Wednesday the 5th, but actually occults them, though
the events will not be visible. In a rather remarkable "triple,"
on the same day the Moon then invisibly occults Neptune as well. The next day, Venus and Neptune
pass conjunction with each other.
As witnessed above, Venus and Mercury play together in the dawn
hours, even once again coming into conjunction later in the month.
Mercury, which reaches greatest western elongation on Monday the
3rd, is actually the higher of the two, though with the ecliptic rather flat to the
horizon, the apparition is poor. It's far easier to admire
Jupiter, which now rises in Sagittarius before 4 AM.
Switching to the evening,
Mars, which transits the meridian
to the south a bit after 7 PM, just before twilight ends, crosses
over into Gemini near the end of
the week, where it is almost three degrees to the north of the summer solstice. It's with us most of
the night, not setting until 3 AM. Well to the east of Mars, Saturn, nicely set in
Leo to the east of Regulus, is already up at sunset,
and now transits the meridian just before local midnight.
While winter's focus is often on Orion, among the greatest of celestial sights is his
Larger Dog, Canis Major, which lies
to the southeast of the giant Hunter. With Sirius, the brightest star in the sky
twinkling madly under the effect of variable refraction in the
Earth's atmosphere, the Big Dog can hardly be missed. Sirius is
also the southern anchor of the Winter Triangle, which includes Betelgeuse in Orion and Procyon in the Smaller Dog, Canis Minor.
