Arcturus rising...daytime...Arcturus setting

Event Date: November 13th

Time: 5:15 AM

Brief

   Arcturus has been in our evening sky since late winter, although late hours at that time, rising in the east.  Now, with the Sunsets much earlier and twilight time shortening since summer, we still have the star in our western sky for a short time, before losing it below the horizon not long after Sunset.  Try to find it entering atmospheric pollution, or if you find it quickly enough after Sunset, you may still notice a reddish-orange color for a brief time.  With a northern declination that allows us--from our latitude--to see it for over 14 hours, Arcturus will return to our pre-dawn skies shortly before 4 AM tomorrow.

   Image one shows it high in the east during civil twilight this morning, nearly the same altitude as nearby Venus.  Image two represents the star low in the west-northwest.

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

Detailed

   At 19.1º north, Arcturus can be seen circumpolar at very northern latitudes of 71º up to the pole.  Although nearly inhabitable, anyone getting this far north on our globe currently has 24 hours of twilight-ish skies, as our Sun is at a similar declination as Arcturus south of the Sun (18.2º).  Therefore, when the Sun reaches the same declination as Acturus, it will dip below the horizon at 71º, giving any viewers there slightly darker sky to see Arcturus nearly tangenting the horizon once every 23 hours, 56 minutes: a sideareal day's worth of time.  For the rest of the day, Arcturus doesn't ever get extremely high in the sky.  Of course, for any star with the same declination as the latitude viewed from, it makes a complete circle around the horizon once every sidereal day, yet stays at the horizon-- only moving below or above it as a result of very slow proper motion and precession of the Earth's axis, mentioned numerous times so far here in this blog.  That is, with precession, the spin-top motion of the Earth on its axis means that over the 26,000 year cycle, viewers at locations globe-wide, get to see a section of sky either sink below the horizon, or become more visible.  The closer to the equator we live, the less the sky changes however, since viewers there already see the two halves of the sky equally, when at the equator.