Summer is almost here. Here in midwestern Europe, that means the end of astronomical twilight will not happen again until the third week of July. Serious deepsky observing this time of year at this latitude will require travel; not to just escape clouds, light pollution and poor transparency but also to be able to enjoy total darkness.
Observers at lower latitudes have no such trouble. But those of use under the grey nighttime skies of northern hemisphere summer need not to worry: everyone will be able to enjoy this week's OotW as it's plenty bright.
This spring, I went on a six night astrotrip to northern France. The skies allowed for 4 nights of observing, of which 2 were very good and 2 were magnificent. I blogged about it.
The final night, even the second to last observation of the entire trip, I logged what I found to be the best observation of them all. A surprising one.
The constellation is Hercules. A large patch of sky that packs a heck of a lot of objects. 3 Bright globulars, lots and lots of galaxies and quite a few planetary nebulae, too.
Hugging the constellation's eastern border, close to a fox and an arrow and with a lyre overhead, is one of them.
18:49:48 +20:50:39 is the position. The name is Humason 2-1. It also goes by Vorontsov-Vel'yaminov 458, PK 051+09.1 and PN G051.4+09.6. Nearest bright star is 112 Herculis, shining bright white at mag. 5.3, just under a degree of arc due northeast. Exactly one degree west-southwest is 110 Herculis a.k.a. John Herschel's 2839th double (WDS18457+2033).
Milton Humason, a high school dropout who became a janitor who became an astronomer who worked with Edwin Hubble, discovered it over a century ago:
Direct photographs made with the Hooker telescope on June 23, 1922, show the planetary image to be slightly elongated as compared with the perfectly round images of the adjacent stars. With the same instrument a minute disk about 3" in diameter is discernible visually. No central star seen. A rough estimate of the visual magnitude of the nebula as a whole is about 11.5.
There's not a lot of imagery available for our OotW and the images that can be found, are all overexposed. That means it's up to us stargazers to take a closer look and to find out what this nebula is all about.
It was in August 2019 when I first observed this planetary. As the images in the observing guide reveal, there's a mag. 11 star (TYC1596-02617-1) just to the south-southwest, which makes for an easy comparison and will leave no doubt as to the nature of its nebular neighbor, that at first sight may appear stellar.
17mm Nagler T4: Stellar without AV, resembles a mag. 10.5 star. Just not stellar with AV, a small sphere when compared to stars in the vicinity. A small but nice nebula, not very faint.
17mm Nagler T4, Lumicon OIII / UHC: The OIII filter has a marginally better effect than the UHC filter.
9mm Nagler T6: Using this magnification the nebula is not stellar without AV, with AV the nebula is clearly larger and is gradually subtly brighter towards the middle. Centrally subtly darker, a ring shape seems to be subtly discernible.
9mm Nagler T6, Lumicon OIII: Using this filter, without AV, the nebula is clearly not stellar.
9mm Nagler T6, Lumicon UHC: Using this filter the nebula is even in brightness.
Back then, I did not up the magnification any more. Working out the observation, I did add it to my notes, to make another attempt in a future session, as I suspected there could be more to this object.
The early morning of 30 April of this year, at the end of a very rewarding session with my 14" SCT, filter slider in place and Naglers for high magnifications within arm's reach, I observed it once more.
17mm Nagler T4, Lumicon UHC: Using this filter the nebula is not stellar without AV and is slightly elongated east to west, seems to consist of two lobes, a slightly larger eastern and a smaller western. Somewhat resembles a double star, which is notable.
17mm Nagler T4, Lumicon OIII: The effect of this filter, without AV, is equal to that of the UHC filter with AV. With AV the nebula is more elongated.
Hmmm... two lobes? Let's investigate that.
5mm Nagler T6: Using this magnification, unfiltered, the nebula is just not stellar and is slightly elongated east to west with AV. No lobe is discernible but there is a faint outer halo.
5mm Nagler T6, Lumicon UHC: Using this filter a ring-shape is clearly visible, the ring is brightest on the SE side. the SE half of the ring is brighter than the NW side of the ring is.
I knew it!
5mm Nagler T6, Lumicon OIII: Using this filter a ring-shape is unmistakably visible, centrally clearly dark and it is evident that the SE 3/5 of the nebula (more than half of the ring shape) is brighter than the NW 2/5. This is suspected to be the reason that two lobes seemed to be visible at lower magnifications. A extraordinarily nice and surprising observation! A remarkable object.
I was mesmerized. Truly stunned. Spent a good fifteen minutes staring at this object. Switched back and forth between magnifications, filtered and unfiltered and twisted my focus knob to the point of overheating as I want to be sure that what I was seeing was not an image like an out-of-focus star.
The nebula is a ring, there's no doubt about that. A ring of uneven brightness. At first, I described it as the southeastern half of that ring appearing brighter. But it's more than half. Using an OIII filter it's dark as the night in the middle. As it is so very bright, it even appeared a bit sparkly with use of the OIII filter.
Truly a ringside view.
3.5mm Nagler T6: Using this magnification, unfiltered, the nebula is a round glow and an outer halo is very faintly visible.
3.5mm Nagler T6, Lumicon UHC: Using this filter the ring shape is visible, but the shape is clearer with 5mm., there is barely anything of the dark central part visible anymore.
3.5mm Nagler T6, Lumicon OIII: Using this filter no dark central part is visible, but is clear that the SE half of the nebula is brightest.
I switched back to 5 mils and remained glued to my eyepiece into morning astronomical twilight.
As I post this, Humason 2-1 transits around the middle of the night and will continue to be positioned optimally well into October.
I hope I convinced you it's one to bag this summer or early fall. So have a go at it! And please be sure to report back.
