Spring Arc pre-dawn setting

Date: May 9th
Time: 4:00 AM

Brief

   Back in February and March not long after dark, we saw the Spring Arc stars rising in the eastern half of the sky.  Now, a couple months later and not long before dawn, those stars of the Big Dipper, Arcturus and Virgo are still above the horizon, yet in the west and getting lower.  As seen from our latitude and other mid-northern ones, Spica is first to set first, even though it is the last to rise, after the Dipper handle stars and Arcturus.

Detailed

Looking at the celestial grid in the image, it reminds us why Spica is the last to rise and first to set: it is the furthest south of the stars. 

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

   As seen from the mid-southern latitudes, it would be the first to rise and last to set, while the Big Dipper would spend alot less time above the horizon.  Arcturus, at 19º north, is best viewed from that hemisphere, but can still be viewed easily at southern latitudes near the equator.  For how long southern viewers see this bright orange star, depends on what evening of the year they start viewing.  When seeing Arcturus when it is at opposition, rising at Sunset in the spring, it is up all night long; this is the same as planets being at opposition, although the stars are fixed.  If a viewer there--or even from the northern hemisphere--starts viewing Arcturus when it is in the west at Sundown, it will only be seen for a small amount of time.  Time Arcturus and the other spring arc stars daily, as they are seen in the same part of the sky about four minutes earlier each day. 
What other asterisms do you see during the night?  Tomorrow, I will remind of one very popular one, which is now rising very shortly after dark, and high in the sky for the entire night after that!