Guest guest Posted July 12, 2000 Report Share Posted July 12, 2000 In a message dated 7/12/2000 7:58:55 PM Eastern Daylight Time, chiropter writes: > As the orbit of the Earth is an ellipse of some eccentricity, with perihelion > in early January and aphelion in early July, Northern Hemisphere Summer is > actually about five days longer than Northern Hemisphere Winter, but the > dates given for the equinoxes are exactly halfway between the solstices. > > Does anyone out there know the resolution to this anomaly ? No, but -- I can tell you that the two days of the year when sunrise and sunset are as close to " exactly " 12 hrs apart are usually *near* the Equinoces rather than *on* them. Still, from the day before the Equinox through the day after -- weather permitting -- shadows will draw a virtually straight line that runs from " due " west to " due " east. Try it on the next sunny Equinox if you don't believe me. Later, Kevin/Baraka Quote Link to comment Share on other sites More sharing options...
Guest guest Posted July 13, 2000 Report Share Posted July 13, 2000 Gentlefolk, Belovéd of Our Lady and Lord, StarDate, the University of Texas McDonald Observatory's syndicated daily radio show, raised an interesting point back on 3 July. [For the full text of the article go to http://stardate.utexas.edu/radio/sd_search.taf?f=detail & id=20000703] As the orbit of the Earth is an ellipse of some eccentricity, with perihelion in early January and aphelion in early July, Northern Hemisphere Summer is actually about five days longer than Northern Hemisphere Winter, but the dates given for the equinoxes are exactly halfway between the solstices. Does anyone out there know the resolution to this anomaly ? Blesséd Be ! Bat Quote Link to comment Share on other sites More sharing options...
Guest guest Posted July 14, 2000 Report Share Posted July 14, 2000 As the orbit of the Earth is an ellipse of some eccentricity, with perihelion in early January and aphelion in early July, Northern Hemisphere Summer is actually about five days longer than Northern Hemisphere Winter, but the dates given for the equinoxes are exactly halfway between the solstices. Does anyone out there know the resolution to this anomaly ? Blesséd Be ! Bat The movement of the Sun in longitude is unequal throughout the year, due to Kepler's 2nd law which requires that equal areas be covered in equal times. At aphelion (Sun's apogee) the Sun moves slower (about 57' a day) and at perihelion (Sun's perigee) it moves faster (about 61' a day). This difference is added to the fact that the seasons are not exactly aligned with the line of apsides or semi-major axis of the orbit (the aphelion-perihelion line). In 1246 AD the Earth was in perihelion at the time of the Winter solstice (i.e., the 2 axis were perpendicular or perfectly aligned: spring=summer, fall=winter), but the seasons slowly shift with the precession of the equinoxes, and at present they form an axis of 11 degrees with the apsides line. The result is that the durational proportion of the seasons is almost never a 2:2. The duration of (northern hemisphere) Winter is now about 89.0 days, Spring 92.8 days, Summer 93.6 days, and Autumn 89.8 days. In other words, the Sun stays at present 7.6 days more in the northern hemisphere than in the southern hemisphere, and the longest season is the (northern) Summer, 4.6 days longer than the Winter, which is the shortest. The relative duration of each season changes slowly with the precession of the equinoxes. For example: the 2 axis were aligned (besides 1246 AD) in the year 4081 BC, when the Earth was in perihelion at the time of the Fall equinox (Spring=Winter, Summer=Autumn...) Asbolo. Get Mail – Free email you can access from anywhere! / Quote Link to comment Share on other sites More sharing options...
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