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Object of the Week October 18, 2015 - NGC 2022
Object of the Week October 18, 2015 – NGC 2022
NGC 2022, PK 196-10.1, PN G196.6-10.9
Constellation: Orion
Type: Planetary Nebula
RA: 5h 42m 5s
Dec: +09° 05’ 11”
Size: 22” x 17”
Mag: 11.7
Central Star Mag: 14.9
Mean Surface Brightness: 18.7 mag/arcsec2
A certain harbinger of the winter season in the Northern Hemisphere is the sight of the constellation Orion in the southeastern sky. Although Orion is a winter constellation which doesn’t transit the meridian until January, I have found the autumn months to be an ideal time to observe it as it rises during the early morning hours; the time when the skies are often at their steadiest and light pollution the least impactful. Not to mention that the outdoor temperatures are much warmer in October than in January. So it was earlier this month in just such a situation, I turned my 15” f/4.5 reflector to Orion and quite accidentally came across NGC 2022, until that moment unknown to me.
After conducting a literature search through observing guides and handbooks, then researching this object on the web, it is safe to say that NGC 2022 is a lesser known, if not an obscure object. Why I’m still not sure, but it isn’t because of its magnitude of 11.7, or even its mean surface brightness of 18.7. It is a bit small, however it takes to high power quite well particularly under the best sky conditions.
William Herschel discovered NGC 2022 on December 28, 1785. In his discovery notes he records for H IV-34: “Considerably bright, nearly round, like a star with a large diameter, like an ill-defined planetary nebula.” Indeed NGC 2022 is a planetary nebula.
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NGC 2022’s shape is a prolate spheroid (like an American football) which is surrounded by a spherical shell of fainter matter. The planetary nebula’s characteristics place it rather early in its evolutionary cycle. At a distance of approximately 8,100 light-years the true physical extent of the its central ring measures approximately 0.8 x 0.6 light-years, while the much fainter outer ring measures 1 light-year in diameter. The HST image of NGC 2022 shows remarkable structure within the planetary. This dynamic structure is attributed to “interacting winds”, i.e., the interaction of different temperature gases.
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Also visible in the HST image is the central star with a nominal magnitude of 14.9. The 1988 paper "Magnitudes of central stars of planetary nebulae" by Gathier and Pottasch gives a visual magnitude of 15.92, though also refers to the earlier results of 14.9 and 14.8. That's a pretty large discrepancy. In any case, a magnitude like this is always going to be misleading based on the bright background of the nebula.
Locating NGC 2022 is easy - it lies in a prominent part of northern Orion just 1.8 degrees southeast of the 3rd magnitude star Meissa (Lambda Orionis).
With my 15” at 214x, under heavily light polluted skies (SQM 18.98) and less than average transparency I saw NGC 2022 easily. My notes reflect that I found the planetary to be surprisingly bright, nearly circular in shape, having a ghostly appearance with uniform brightness throughout, other than a smidgen of brighter circumference in one small arc, strong hint of bluish tint, no inner structure visible, central star not visible. Tried 286x with no significant differences observed.
A survey of observing reports on the web reflects observations in scopes ranging from 5” to 48”. In the smaller scopes the planetary takes on a stellar appearance and can easily be missed. Once located it can be detected at low power. In Deep Sky Companion: Hidden Treasures, Stephen O’Meara says: ”At 60x, the nebula is a very small, pale gray, and highly noticeable disk, nicely condensed; it truly look like a distant gas-giant planet.” At 282x in a 5” scope O’Meara can start to detect structure within the core. Another observer with a 13” scope under exceptional transparency and seeing reports: “A truly great night 100X--obvious dot. 220X--pretty bright, pretty small, little elongated 1.5X1 in PA 0. There is no central star at 220X. 330X--some difficult structure is seen, mostly averted vision only. The east side is consistently brighter than the west side. There are brief glimpses of a stellar spot offset to SE. All this detail is at the limit of the 13". The central star is never held steady, averted vision helps it to stand out and it is seen about 30% of the time at high power.” It seems to require scopes of 18” or larger and high power to ferret out structure in the nebula. Detecting the central star is even more challenging it seems. Though aperture is certainly an enable, it is the overall sky conditions that will make or break the observation of the central star
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Now it is your turn to chase NGC 2022. You have plenty of time and hopefully many opportunities this observing season to catch the brightest planetary nebula in Orion.
As always,
"Give it a go and let us know!
Good luck and great viewing!"
