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02/03/2015 – Ephemeris – Jupiter is really big and spins really fast
Ephemeris for Tuesday, February 3rd. The sun will rise at 7:59. It’ll be up for 9 hours and 54 minutes, setting at 5:53. The moon, at full today, will rise at 6:01 this evening.
Jupiter will appear to the left of the full moon tonight. The Galilean moons will be spread out with Callisto by its lonesome on one side then Europa, Io and Ganymede spaced out on the other. Jupiter’s cloud bands show the great planet’s rotation, and that the moon’s orbit over Jupiter’s equator, like most of the moons of the other planets. The clouds are whipped into parallel bands by Jupiter’s rapid rotation. Here’s a planet 11 times the diameter of the Earth, thirteen hundred times the volume, and over 300 times the mass of the Earth, rotating nearly two and a half times faster than the Earth. The equatorial rotation is 9 hours 50 minutes. The rapid rotation squishes the planet noticeably, which the cloud stripes visually enhance.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Rocking animation of the early stages of the shadow show on Jupiter. Callisto’s shadow already on the planet while Io’s shadow is just entering. Also Io’s transit is starting., following its shadow on the planet. Credit: Scott Anttila.
The above animation which I first posted last week demonstrates three of my points about Jupiter. The planet rotates rapidly, it’s polar diameter is shorter by about 7% than the equatorial diameter, and the satellites orbit over its equator. Jupiter also has a small axial tilt of 3º compared to the Earth’s 23 1/2º. As an aside we’re in the “season” where the satellites occult and eclipse each other.
Telescopic Jupiter tonight (9 p.m. February 3, 2015) as described in the text of the program. Created using Cartes du Ceil (Sky Charts).
02/02/2015 – Ephemeris – Ground Hog Day and other Cross-Quarter days
Ephemeris for Ground Hog Day, Monday, February 2nd. The sun will rise at 8:01. It’ll be up for 9 hours and 51 minutes, setting at 5:52. The moon, 1 day before full, will set at 7:26 tomorrow morning.
If Punxsutawney Phil, the groundhog in Punxsutawney, PA sees his shadow we’re supposed to be in for 6 weeks of winter, otherwise spring is just around the corner. The way the seasons really work, is that Ground Hog day is about half the way from the winter solstice to the spring equinox. In reality calendar-wise winter is about 12 weeks and 5 days, so we only have 6 weeks a few days to go of winter anyway. Groundhog day, May Day, and All Saints Day are holidays near cross quarter days, which are said to mark when seasons are half over. It seems no one cares when summer is half over around the first of August when Back to School Sales used to start. Of course now those sales seem to start the day after school lets out in June.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Poor Punxsutawney Phil, rousted out of his mid winter nap. They might be in the middle of a blizzard today. Credit: http://www.fuzzytoday.com
Bob Moler's Ephemeris Blog 