The Spider and the Fly...

NGC 1931 and IC 417

Objects: NGC 1931 (star cluster with emission/reflection nebula Sharpless 2-237, IC 417 (Sh2-234, Spider nebula, with star cluster Stock 8)
Type: Emission Nebulae 
Constellation: Auriga
Distance: 7500 light years

Dates: 12th. March 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 3 x Red (300s, 2x2 binned), 3 x Green (300s, 2x2 binned), 6 x Blue (450s, 2x2 binned), 9 x 600s H-alpha, flats for each channel, no darks (hot pixel removal in Astroart).

Stellarium map showing field of IC 417

Between Theta Aurigae and Iota Aurigae (the two southernmost stars of the “kite” of the constellation of Auriga) lies a string of emission nebulae. The above image shows another two faint areas of nebulosity lying between the brighter and better known nebulae IC 410 and IC 405 and the "Pumpkin Patch".

Two large OB associations have traditionally been identified in the constellation of Auriga, aligned one behind the other. The first is indicated with the abbreviation Auriga OB1.  Twelve stars of the spectral classes O and B were initially designated as effective members of the association, to which are added three red supergiants at the end of their life cycle. The suggested distance was about 1750 parsecs and was therefore placed on the galactic Arm of Perseus.  The second association is indicated as Auriga OB2 and eight class O and B stars were associated to it, mostly on the main sequence; its distance was indicated at least 6300 parsecs, i.e. in a remote area of the outer disk of the Milky Way, on the Cygnus Arm.


The estimated distance of IC 417 suggests it to be close to the Auriga OB1 association.

The image itself is fairy noisy, as clouds cut short the imaging session and I was only able to grab nine Ha frames to use as luminance: not that I would have been able to get to many more anyway, as the object was sinking into the western horizon.