Posts Tagged ‘Orion Arm’

02/13/2018 – Ephemeris – Looking out the thin side of the Milky Way’s disk

February 13, 2018 Comments off

Ephemeris for Fat Tuesday, February 13th. The Sun will rise at 7:46. It’ll be up for 10 hours and 22 minutes, setting at 6:08. The Moon, 2 days before new, will rise at 7:07 tomorrow morning.

With Orion and the winter stars grabbing our attention in the south, let’s look to the northeast to southeast where the stars are not as many, and with the exception of the Big Dipper and some other stars, not as bright. The inner stars of the Big Dipper are part of a sparse star cluster only about 80 light years away. The reason for the sparseness is that here we are looking out the thin side of the Milky Way’s disk.  It will be our spring sky. To the west is the autumn evening skies. The thick part of the disk runs from the south-southeastern horizon, to just west of the zenith to the northwestern horizon. The reason the Milky Way isn’t as bright as the summer sections, is that we are looking away from the center to the outer spiral arms. We are in a small arm with the Great Orion Nebula.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


he dome of the sky

The dome of the sky at 9 p.m. February 13, 2018 showing an enhanced Milky Way. Showing also the drop off in stars off that band to the east and west. Click on image to enlarge.  Created using Stellarium.

Our place in the Milky Way.

Our place in the Milky Way. Note that we appear to be in a barred spiral galaxy.  The arms are numbered and named.  3kpc is the 3 kiloparsec arm. 1 parsec = 3.26 light years. The Sun is about 27,000 light years from the center. Credit NASA and Wikimedia Commons, via

Our galactic neighborhood

Our galactic neighborhood on the Orion spur or arm. Credit R. Hurt on Wikimedia Commons, via

The summer and winter Milky Way viewing directions.

The summer and winter Milky Way viewing directions. During Spring and Autumn, we look out the sides to the universe beyond. Credit: NASA with annotations by Bob King at Universe Today.