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Yellow tree

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.
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