Object of the Week, September 17, 2017

The UMi dwarf galaxy (UGC 9749) and IC 1110

Dwarf galaxy and edge on galaxy
Ursa Minor
RA 15h 12m 05s
DEC +67d 21m 45s
Magnitude 14.9
Size: 1.4 x 0.4 arc minutes
(coordinates, magnitude, and size are for IC 1110 because it’s much easier to see than the UMi dwarf galaxy, UGC 9749.)

UMiDwarfand IC1110_wikisky.JPG

These two mismatched galaxies could hardly be more different. The UMi dwarf is a satellite galaxy of the Milky Way and is about 225,000 light years away, while IC 1110 is an edge-on galaxy approximately 157 million light years away.

Their apparent sizes are vastly different too – IC 1110 is a respectable 1.4 x 04 arc minutes but the UMi dwarf is a huge 30 x 19 arc minutes. So even though it's listed magnitude is 11.9, it has a surface brightness so low I can’t find any reference of it. Suffice to say it’s barely brighter than the sky background.

My observing notes from 2013 bear this out:

“IC 1110 was immediately obvious at 131x but not UGC 9749. Only when centering IC 1110 in the field of view did I notice the area where 9749 should be was ever so slightly brighter than elsewhere. The lack of foreground stars here is a help too. This effect was even more pronounced at 253x. 21.77 SQM.”

UMiDwarfandIC1110_crop.jpg

My sketch shows only about half the length of the UMi dwarf, but compared to the photo from Wikisky.org it seems to be brightest part.

IC 1110 is just two degrees west from the magnitude 5.13 star, HD 136064 so it’s easy to star hop to, so on the next dark and transparent night…

"GIVE IT A GO AND LET US KNOW"