Object of the Week, January 10th, 2021 – IC 2169... and Friends

[Paul Alsing]

Monoceros - Reflection Nebula
R.A.: 06h31m00.0s Dec.: +09°54'00"
Size: 25.0'

Well-placed at this time of the year, IC 2169 = IC 447, also known as Dreyer’s Nebula, is a very large diffuse reflection nebula in Monoceros, very close to the much larger and more well-known complex that encompasses the Cone Nebula, the Fox Fur Nebula, the Christmas Tree Cluster, and the variable star S Monoceros. As such, IC 2169 just does not get the attention that it deserves! Here is the April 12th, 2007 APOD of the whole area…

APOD April 2007.jpg

… and IC 2169 is the much smaller blue area on the right-hand side of the photo. Although faint, IC 2169 is still an interesting object to view, and with a long dimension of about 25’ it is almost as tall as the full moon! The brightness of the reflection nebula varies quite a bit over its irregularly-shaped surface, but only very delicately, with no sharp edges that I could detect. Here is a copy/paste from my SkyTools program, along with a cropped photo by Ken Walker that is approximately the same area…

IC 2169 pano.jpg

… and there is a 30 arc-minute circle on the chart for reference so you can get an idea about the various distances involved with the field.

There are a couple of small dark nebulae within IC 2169’s boundaries that make a triangle with a nice double star (A 2816 on the chart, 1.6” sep) and even a tiny open cluster, Alessi 14, just outside the nebulosity.

As you can see, there are several other nebulae within a degree or so, including IC 446 = IC 2167, NGC 2245, and NGC 2247 around the variable star V700 Mon. All of these are bright enough to view through telescopes of all sizes and you can spend a lot of time in this area just cruising around and enjoying an area of the sky that is mostly overlooked.


As always, give it a go and let us know.

[Uwe Glahn]

I can contribute two descriptions of IC 447, even when observed more often in the past, and one sketch of IC 446 and one sketch of NGC 2245.

IC 447
4", 31x, NELM 6m0+
bright, wonderful star field in the near of Christmas tree cluster, 1:2 N-S elongated, structureless

27", 113x, NELM 6m5+
whole object to large for the 27-inch, dark structure NW of V727 Mon

IC 446 (0,6° N of IC 447)
sketch: 27", 293x, NELM 7m0+, Seeing IV
IC446.jpg
home

NGC 2245 (0,5° NE of IC 447)
sketch: 27", 293x, NELM 7m0+, Seeing IV
NGC2245.jpg
home

[Steve Gottlieb]

Here are a couple of observations of IC 2169 = IC 447 (reported both visually and photographically by E.E. Barnard, hence the two numbers).

24" (1/31/14): picked up unfiltered at 200x, though low contrast as the entire field is patchy in faint stars and affected by some dust. Seems roughly 20'x10, elongated N-S and includes several bright stars (Cr 95) with mag 7.9 HD 46005 near the center (illuminating star), mag 8.9 HD 258853 near the south end, and a mag 9.3 star at or beyond the NW end. The contrast is significantly improved at 125x using a NPB filter and the outline is better defined, particularly at the southern end. Although the nebulosity is slightly brighter to the south of HD 46005, there are no high surface brightness sections.

18" (2/4/08): at 175x unfiltered, this is a huge, interesting reflection nebula, ~25'x18', elongated N-S with an irregular outline and subtle variations in brightness. A number of mag 8-10 stars are superimposed, including mag 8 HD 46005 (illuminating star) which is part of a 10' N-S string of four brighter stars on the east side. Nearby reflection nebulae include NGC 2245 ~30' NE, IC 446 35' N and NGC 2247 40' NE (this group forms the association Monoceros R1).

I only have an older observation of IC 2167 = IC 446 (again the two designations are from Barnard, first visually in 1888 and then photographically in 1894 at Lick Observatory):

17.5" (1/23/93): fairly faint reflection nebula surrounds a mag 10-11 star. This bi-polar nebula is fairly large, about 2.5' diameter. Appears to extend further (or is brighter) on the south side. Bordered by three collinear mag 13 stars on the south side.

William Herschel discovered NGC 2245. Here's an observation from exactly 30 years ago (almost to the day!)

17.5" (1/19/91): bright, fairly large, about 3' diameter, elongated SW-NE. Fans out to the southwest from a fairly bright mag 11 star at the northeast end. Fades smoothly into background. Located 2' WSW of mag 8.0 SAO 95816. Reflection nebula NGC 2247 lies 12' NNE.