OR: Lake Sonoma - October 23 2025 - Part 2
Muriel Dulieu Holzer
M 76, the Little Dumbbell Nebula in Perseus, is a small planetary nebula with a curious two lobe shape. Its particular dumbbell shape is due to the fact that it is a bipolar planetary nebula meaning that the dying central star ejected gas more strongly along its poles than along its equator. The cause was probably that the central star had once had a binary companion star. The hypothetical companion star isn’t seen in the Hubble images, but it could have been swallowed by the central star.
The Little Dumbbell Nebula was originally discovered by Mechain in 1780, who reported it to Messier. Later on when William Herschel observed it, he thought it was two nebulae side by side so the two lobes were catalogued separately as NGC 650 and NGC 651. It was only found in 1891, by Isaac Roberts, that M 76 is a single nebula.
The real three dimensional shape of the Little Dumbbell Nebula is of a torus or dense ring of gas and dust surrounding the central star, with two large faint bubbles of gas on both sides of it. But we see the planetary nebula edge-on, with the central bar being the waist of the torus, and the two lobes being the expanding bubbles of gas flowing away from the poles.
Looking at it both in the 10” and in Steve’s 14.5”, I could see the nebula’s distinct hourglass shape and its two lobes with the lower one being a little bit brighter and more defined. Then I looked at it again with a NPB nebula filter that Steve kindly offered me to borrow. A NPB filter (Narrowband Pass Filter) is a filter that lets through only a narrow range of wavelength, H-Beta (Hydrogen-beta) and O-III (doubly ionized oxygen), which correspond to the range emitted by ionized gases in emission nebulae. With the filter, the background appears darker which makes the nebula pop. With it, it was easier to see the outer glow around, that extends left and right around the nebula.
I was curious to try the filter on other objects, so I looked at the Helix Nebula in Aquarius, also called the eye of God. This is also a planetary nebula, one of the largest and the closest from us, lying at a distance of around 650 light years.
Contrarily to the other planetary nebulae I was looking at that night, the Helix Nebula is a polypolar planetary nebula and not a binary planetary nebula, which means that it went through multiple, episodic bipolar outflow events at different orientations due to precession of the bipolar outflow. But its central white dwarf also has a candidate low-mass binary companion in a few days' orbit.
Without the filter I couldn’t see it, probably because, even though its magnitude is 7.3, its light is spread over a large area so its surface brightness is extremely low.
With the NPB filter it suddenly appeared as a white large ring. The middle of the ring was not as dark as I expected, only slightly darker than the ring.
My biggest surprise was to see the colors appear on the picture taken by the Seestar S50, from red on the outer ring, to yellow and green in the middle. The Seestar has built-in RGB filters and does a beautiful job amplifying the oxygen and hydrogen emission lines through stacking (see picture below).
After looking at the Little Dumbbell Nebula, I had to look at the other Dumbbell Nebula, M 27, in Vulpecula.
The Dumbbell Nebula was the first planetary nebula ever discovered. Its central star is one of the hottest known, about 85 000 K. K.M. Cudworth of Yerkes Observatory noted that the central star may have a yellowish star as a companion. It is similar to the Little Dumbbell Nebula as they are both bipolar planetary nebulae. The differences lie in the fact that M 27’s absolute size is larger than the little dumbbell nebula and its surface brightness is lower probably because it is older. The size of the Dumbbell Nebula appears even larger as it is closer to us than the Little Dumbbell Nebula. Their appearance also differs from the fact that the Dumbbell Nebula is seen side-on (60-70 degrees from the polar axis) while the Little Dumbbell Nebula is seen edge-on (85 degrees from the polar axis).
In my 10” with the NPB filter, I could see a bright core in the shape of an apple core with a round glow around it.
I was reading about the cusped knots and dark tails embedded in the Dumbbell Nebula’s bright region. The knots are small dense clumps of gas that glow where ultraviolet light from the central star ionizes the gas. Behind each knot, the dense material blocks the radiation creating a dark tail. I tried to check those knots and dark tails on my Seestar picture but even though the image of the nebula looks mottled, I couldn’t see them.
Like M 76, the Little Dumbbell Nebula, and M 27, the Dumbbell Nebula, M 57, the Ring Nebula, is a bipolar planetary nebula except that in this case, we are looking at it almost along its axis (30 degrees tilted). The ring is a torus and when looking through the middle, we are actually looking through the fainter polar lobes. Like most of the other bipolar nebulae likely created by systems of binary stars, the central star of the Ring Nebula has a low-mass companion orbiting at a distance comparable to the distance between earth and Pluto.
Looking at it through my 10” with the NPB filter, I could see it clearly but the center part was filled in and looked only slightly darker.
With the NPB filter, I could see the Pacman Nebula’s shape faintly in the 10”.
I’ll have to look again to check if I can see its 8th magnitude primary, HD 5005, and its four companions (that are part of the open cluster IC 1590). The renowned double star observer Sherburne Wesley Burnham discovered its multiplicity in 1871 with his 6” refractor. I also want to check if I can see the dark lanes of obscuring dust and dense knots of gas and dust, bok globules, in which stars may currently be forming. Maybe next time.
The North American Nebula is a large emission nebula in the constellation Cygnus, close to Deneb. It measures 3 degrees North to South, 2.3 degrees East to West, and covers an area more than four times the size of the full Moon. I am using a Baader 8-24 mm hyperion universal zoom Mark IV eyepiece with the NPB filter and the nebula does not fit in the eyepiece at its lowest power, but I could see it. On top of it, I could see a roundish black area which is a dark nebula (LDN 935) supposed to represent the gulf of Mexico.
NGC 7129, the Flower Bud Nebula, is a reflection nebula in cygnus. I couldn’t see it with the 10” and the NPB filter. This makes sense since a reflection nebula shines by reflecting starlight, which is broadband, meaning its light range is spread across the entire visible spectrum. As the NPB filter blocks most of the spectrum of light to pass only specific wavelengths, it blocks most of the light from the reflection nebula as well.
The Cocoon Nebula is an emission nebula and star cluster in Cygnus. It holds a bright red emission nebula, a blue reflection nebula, and a dark absorption nebula. Inside the Cocoon Nebula is a newly developing cluster of stars. There is also a dark nebula, Barnard 168, that looks like a trail going around it and behind it. I could not see the emission nebula with the NPB filter in my 10” dob. Maybe I should have tried to look at this without the filter in order to see the blue reflection nebula, or try with a different filter.
The total magnitude of IC 5146 is 7.2 but this refers to the combined brightness of the central star cluster and the nebula. The nebula alone is much fainter, with a magnitude around 10.0. Apparently it is a challenging object to look at. I will try again when I get access to a bigger scope.
Extremely large cluster (170 arcmin across), very bright, loose, irregular, and awash with a faint nebulous background mixed with dark lanes. The nebulosity sprawls across roughly 3 degrees of the sky. It is difficult to see visually and indeed I could not see the nebula with the NPB filter. SkySafari recommends using an O-III filter, I’ll try that next time on a bigger scope.
I have seen this planetary nebula in Steve’s 14.5” scope with a night vision device before. It is named like this because of its extended ansae (Latin for “handles”) that make it look like Saturn and its rings. But I could not find it this time. Maybe it looks too small in my 10” or maybe I am getting tired.
All of a sudden three cars arrived with blazing lights, driven by a group of young noisy people obviously having a good time. They started doing what I learned to be donuts, raising clouds of dust in the air at full speed in circles. I have never seen or heard of this before. I did not feel too comfortable. It was already 11.30 pm and we wrapped up quickly. A little bit earlier than planned but with almost a two hour drive back, this was not a bad time to leave. The end of a great evening!
