Summer Triangle setting late at night

Event Date: October 12th
Time: 1:00 AM


Brief

   Let's speed up the clock to past midnight from yesterday's entry, about 5 1/2 hours later, and look at the location of the Summer Triangle.  While transiting at about 7:30 this week, it is still high enough to see all three stars at the time above, albeit barely if obstruction from trees and tall buildings are an issue.  Taking a look, Vega and Altair reach the same altitude as seen from out latitude when about 20º high.  Deneb, being further north and east of Vega, sets later, and is the lone star of the triangle still barely above the horizon at the break of dawn.

click on image to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

   The way we see the triangle above, is about where we see the stars once dark enough in mid-winter.  By then, it seems to get lower faster, since the Sun starts setting later and twilight lasts longer.  For now, we can enjoy seeing it high in the sky for the evening until about early November.  At that time, we have the end of daylight savings, meaning that in just one day, we see the triangle at the same position an hour and four minutes earlier.  That is as if two weeks suddenly pass by!  As we know, stars rise and set about four minutes earlier each day, so an hour earlier about every 15 days, or a little over two weeks.  Once we start losing the Triangle early in the evening during winter, there is still an upside: we start seeing it rise before Sunrise: Vega and Deneb further north than Altair, spend less time below the horizon, while Altair is visible to the unaided eye again rising in the east by late January.