Alan, > 1) Can I tell from this view when the vernal equinox is? Nothing > seemed to be unique about March 20 just by simply looking at the > animation of the sun at noon over time.
Well, the sun crosses the celestial equator at the time of the vernal (and autumnal) equinox, so if you turn the RA/DEC grid on, you can see when the sun crosses the celestial equator. > > 2)The ecliptic intersects at due E and W on 6/20 and 12/20, which I > understand. But I don't understand how to explain the intersections > at other times. For example, the eastern intersection seems too far > east right now. > By right now, I gather you mean at the right now time of the day. In fact, in a period of 24 hours the intersection of the ecliptic with the horizon will oscillate back and forth from azimuth 60 to azimuth 120 (approximately, at my latitude of 39 degree N; NE to SE, back and forth as time elapses). The variation depends on the latitude (greater excursion at higher latitudes). I believe that the extrema don't change over the course of a year, but at any given time of the year and time of day, the intersection point will be at different points. In other words, if the ecliptic intersects the East horizon point on a given day and time, on a different day at the same time, and also on the same day at a different time, the intersection will be in a different place. There's both a diurnal and an annual effect. Does this answer your question? Dick ------------------------ Yahoo! Groups Sponsor --------------------~--> Has someone you know been affected by illness or disease? Network for Good is THE place to support health awareness efforts! http://us.click.yahoo.com/RzSHvD/UOnJAA/79vVAA/1.XolB/TM --------------------------------------------------------------------~-> To Post a message, send it to: [email protected] To Unsubscribe, send a blank message to: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/skychart-discussion/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
