C2, Bow-Tie Nebula in Cepheus

Non-Messier Deep Sky Objects C2, Bow-Tie Nebula in Cepheus

Target	Type	R. A.	Dec.	Constellation	Magnitude	Size
C2 (NGC 40)	Planetary Nebula	00h 13m 01s	+72° 31′ 20″	Cepheus	10.6	0.6×0.6 arcmins

Overview

The Silver Needle galaxy is a beautiful edge-on spiral discovered by William Herschel in November 1788.

The star in the centre of this glowing veil of gas is dying and lighting up its formerly-ejected outer layers. It’s a small object, only one light-year across, and about 2,700 light-years away. It will gradually fade over time with the Earth-sized white dwarf being all that’s left of it in about 30,000 years from now.

The central star is about 7,000 times brighter than our sun but is only half its size.

C2, planetary nebula in Cepheus (source).

Finder Charts

C2 is a hard object to find without binoculars. It’s small and faint, and there aren’t many guiding stars to help you close in on it.

This first sky chart, from SkySafari 6, shows the sky looking west at 10:00 p.m. in mid-August. Stars on this chart are shown to magnitude 5.0 and the moon and planets are not shown.

The best way to identify area to search for C2 is to locate the easily identified ‘W’ of Cassiopeia, and use it and Ursa Minor (the Little Dipper) to locate Cepheus. This constellation looks like a child’s drawing of a house. We need the star at the tip of the ‘roof’, called Errai. You should also locate Kappa Cassiopeiae, which is above the central star of the ‘W’ shape.

All of these features, along with the Big Dipper, are highlighted in this first chart.

[C2-1] Refine your search to the area between Errai and Kappa Cassiopeiae. Click for full-screen.

In this second chart. you can see that C2 (shown as NGC 40) lies almost exactly on the line connecting Kappa Cassiopeiae to Errai. It’s closer to Errai and the three faint stars also hugging the line (shown with the dashed oval) give a clearer view of where to look.

Note that the stars in this chart are shown to magnitude seven. The fainter ones will only be visible through a magnifying finderscope or with binoculars.

[C2-2] A line of three magnitude six stars shows the route from Errai to C2 (NGC 40). Click for full-screen.

Finally, we can see that a 1° field of view, marked by the blue ring, contains both the most southwesterly of the previously identified three stars (shown inside dashed circles) and NGC 40. Note Errai is still in the top left hand corner of the chart.

[C2-3] NGC 40 fits inside the same 1° field of view as the southeastern most of the three mag. 6 stars. Click for full-screen or download the pdf below.

Now you have this faint spectacle in your eyepiece, what should you expect to see?

Individual Telescope Views

The following views will help you find C2 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Stars are shown to magnitude 11.0 and the star referenced above in the 1° field of view is the brightest one diagonally opposite NGC 40, midway between N and W in the 1.5° field of view rings, in these charts.

Each image can be clicked on for a full-screen version.

Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope

Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal

Mirrored View – Refractors and Cassegrain models with a star diagonal show this view

Observation

First of all, remember this is a small object. On first pass on a low magnification, it looks little different to a star. Only averted vision gives a clue as to its unimposing presence.

With increased magnification it becomes more obvious with averted vision, but far from stand out.

To separate out the nebulosity from the central star here, we need good seeing conditions and a high to very high magnification. It’s only under these conditions that you can challenge yourself to see some shape and texture in the nebula. You’ll see two brighter spots on opposite sides to each other, and the fact that this nebula is not quite circular.

Do not be too hard on yourself if you don’t succeed at first; this is one of the toughest challenges inside the VAC and I for one wonder why Sir Patrick Moore included this view in his list.

PDFs for Printing

Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [C2-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.