Arcturus rising late evening

Event Date: January 24th

Time: 12:00 AM

Brief

   During this time of year, we welcome back a bright star to the post-midnight skies, rising shortly before that, as seen from locations west in their time zones.  Arcturus!  I mentioned this star several times at the beginning of this blog last spring, as it marked the center of the Spring "arc", sandwiched by the last handle stars of the Big Dipper and Spica.  The latter doesn't rise until later in the morning, being further south and east of Arcturus.  As for the Big Dipper, it is already high in the northeast before midnight.  The image here shows the Dipper with no stick figure.  Look where Arcturus is low in the north-northeast, and look to its upper left for the Dipper stars.

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

Detailed

   According to this table Arcturus is the forth brightest star as seen from Earth, at about magnitude

-0.04, although it and later-to-rise-Vega are nearly identical in apparent magnitude; the latter only very slightly "dimmer" and magnitude +0.03.  There isn't a noticeable difference through optical aid, and especially with the eye between these two.  At 37 light years away, I can personally say as I write this, that when I look at Arcturus early in the morning sky, I am seeing the light the way it was when I was either an infant, or just before I was born, depending exactly how far the star really is. Stars are usually estimated to the nearest whole value for light year distance.  In any case, I can accurately say that I have lived (about) as long as it has taken for Arcturus' light to go from the star to Earth-viewers eyes...pretty cool!  I passed this already with some other bright stars such as Alpha Centauri (4 years), Sirius (8), Altair (17) ,Vega (25), just to name a few.  The next 1st magnitude star that I can look forward to doesn't happen for a few more years: Capella, at 41 years, which is just "a hair" dimmer than Arcturus and Vega.

   Getting back to the star itself, it has an unusual characteristic which makes it very different than many other stars that we see easily: it is "cutting perpendicularly through our galactic disc".  You may remember when I was discussing the Mayan Calendar topic, that I was showing the galactic equator, marking the Milky Way as it circled around us.  To learn more about Arcturus' motion read this excellent description.  It may seem abstract, yet all we really need to know is that Arcturus will be very slightly closer to our solar system in a few thousand years, yet not noticeably.  More obvious, millions of years from now, we will not see this very fast moving star.  In the sky, it is completely unnoticeable on a night-to-night basis, yet it is happening!