|NGC 7092 (Caldwell 39)||Planetary Nebula||07h 29m 11s||+20° 54′ 37″||Gemini||9.19||0.8×0.7 arcmins|
This is a tough challenge for any scope. Not to see it as a star – it’s bright and shows up in all scopes – but to observe the nebulosity. The Clown Face nebula is a small but bright nebula eight degrees southwest of Pollux, one of the star ‘twins’ in Gemini.
William Herschel discovered the nebula in January 1787 and noted it as a “star of 9th magnitude with a pretty bright nebulosity all around it”. More intriguingly, his notes also refer to it as “a very remarkable phenomenon.”
This nebula has various names, commonly known as the Eskimo, Clown Face, or Lion nebula.
At its center is the star that created the outer filaments of blue gas we see today. Once upon a time, the star was like our sun but, reaching the end of its life as a red dwarf, it exploded away its outer shells of gas in a cataclysmic event, leaving the nebulosity we see today. The gas filaments are steadily expanding away from the central star, which is still clearly visible, at about 35 mph (60 kmh).
NGC 2392 is about 6,500 light-years away from us.
This first sky chart, from SkySafari 6, shows the sky looking east at 10 pm in the middle of December. Our nebula is about a third of the way towards overhead from the eastern horizon. Orientate yourself using Orion to jump to Gemini and its two brightest stars, Castor and Pollux.
Stars on this chart are shown to magnitude 5.0 and the moon and planets are not shown.
We need to find a triangle of three similarly bright stars. Zeta, Lambda, and Delta Geminorum are all about magnitude 4 and clearly visible to the naked eye. Locate these and pay particular attention to Delta Geminorum (Wasat) because this is the star that will take us the final part of the journey.
This last star chart shows stars to magnitude 7.0. We need to locate a kite shape of magnitude five stars which has Wasat at its tail. From there, position your view so that 63 Gem. is at the northern side of a 1-degree field. On the southern side, you’ll have NGC 2392 in view.
Now you have this nebula in your eyepiece, what should you expect to see?
The following views will help you find NGC 4392 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 12.0 and the circle is a 1° field of view. 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
You’ll notice a bright star in the lower right hand corner of the image at the top of this page. Because the picture is so ‘zoomed in’ it’s hard to grasp that this star is so close to the nebula that through binoculars, they look like the same star.
Indeed, in a small telescope, you’re more likely to notice an apparent double star than you are the nebula.
What’s great about this nebula is the amount of magnification it’ll tolerate. Don’t be afraid to act as if you’re trying to crack a tight double star apart and use a high powered eyepiece. This will reveal a blue-grey ‘fatness’ to one of the stars, which is what gives away its nebulosity.
You’ll need to use averted vision to study the effect in detail. Looking away from the nebula remarkably switches it on. Out the side of your eye, note the delicate mottled appearance of the shading around the bright central star.
NGC 2392 is known as the Eskimo nebula because photos of it make the central star look like a face surrounded by a fur-lined parka hood. We see that effect because there’s a darker ring between the star and the outer halo. Try and observe this darkening. It will perhaps be impossible in a smaller scope, but a larger model will reveal it under eye aversion.
If you have access to an OIII or light pollution filter, use it to look at this sight. It will help reveal some details in the shells glow, even in a 6″ telescope.
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 [M48-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.