Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. The carbon star
W Orionis stares
redly back at us from the middle of the picture. Orion's Bellatrix is at upper left, while the right
hand star of the belt shines at lower left.
Astronomy news for 9 days starting Friday, February 27, 2004.
Skylights will next appear on Sunday, March 7.
The Moon waxes through its gibbous
phase during this extended period, beginning with first quarter
on Friday, February 27 (during mid evening in North America), and
ending with
full on Saturday, March 6 (just before moonrise). The evening
of Monday the 1st, the Moon will be seen to the north of Saturn, while on
the nights of Friday the 5th and Saturday the 6th it will bracket
much brighter Jupiter.
This week, on the night of Wednesday March 3rd, Jupiter passes
opposition with the Sun, when it
rises at sunset, sets at sunrise, crosses the meridian to the south
at midnight (roughly when formal opposition is actually taking
place), and is in the middle of its
retrograde, or backward, motion. About two hours after
sundown, around 8 PM, Saturn crosses the meridian. Then only three
hours before Jupiter comes into formal solar opposition, Mercury passes
its superior conjunction with the Sun, when it is on the other side
of the Sun from us and completely invisible. Meanwhile, Mars and brilliant
Venus hang out
in the western sky drawing ever closer, Venus now setting around
9:30, Mars two hours later, the early evening sky now containing
all the ancient planets but Mercury.
As a special treat, the week gives us February 29, this "leap
year" occurring only once every four years. The purpose is to
reconcile the days in the calendar to the actual length of the
year, which is close to 365 and a quarter days long. Over a four
year period, the calendar therefore averages 365.25 days. The
problem is that the actual number of days in the year is
365.2422..., so given this simple system (of the original Julian
calendar, after Julius
Caesar), the dates of the equinoxes and solstices creep
forward. This problem is solved in our Gregorian
calendar (after Pope Gregory
XIII of the late 16th century) by dropping leap years in
century years not divisible by 400. Thus 1900 (which falls on the
four year cycle), was not a leap year, 2000 was, and 2100 will not
be. The result is a 400 year average of 365.2425 days, very close
to reality.
What dominates the early evening sky now more than anything else is
Orion (which is starting to slip
a bit west) and his two hunting dogs, Canis Major (the Larger Dog, with Sirius, the brightest star of the
sky) and Canis Minor (the Smaller
Dog, with Procyon). With Orion's
reddish Betelgeuse, these two
stars make the prominent "Winter
Triangle," Procyon east of Betelgeuse, Sirius to the southeast.
Due west of Sirius is the box-like set of stars that make Lepus, the Hare, while directly
below Lepus find the flat triangle that forms Columba, the Dove.
