Target Fun Facts
Sharpless 157, sometimes referred to as the Lobster Claw Nebula, is an emission nebula in the constellation Cassiopeia, approximately 11050 light years (3390 parsecs) from the Earth. It is located on the Perseus Arm and is directly connected to the large OB Cassiopeia OB2 association. The northern part of the cloud has a ring shape, caused by the action of the stellar wind of several giant stars, while the southern sector appears excited by the bright radiation of stars of spectral class O.
NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region emission nebula in the constellation Cassiopeia. It lies close to the open cluster Messier 52. The “bubble” is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575. The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in November 1787 by William Herschel.
SH2-161 lies close to SH2-162 also known as The Bubble Nebula. SH2-161 is a large diffuse nebula surrounding the much smaller (and better studied) SH2-158. The BFS catalog argues that SH2-161 is actually two distinct nebulae in the same line of sight, which they designate SH2-161a and SH2-161b. (Sharpless himself made no such distinction.) Curiously, however, the distance estimates given in the scientific literature for the two nebulae are almost identical despite the quite different velocities quoted for the gas in this direction.
SH2-161a and SH2-161b are separate nebulae at different distances in the same line of sight. One possible reason for the distance confusion involving SH2-161a and SH2-161b might be that some authorities assign the 2800 pc distance estimate given in the original 1982 BFS study to SH2-161a and others to SH2-161b. The BFS note for these nebulae states “It is unclear which HII region is at the distance given in ref. 8”.
SH2-158 is the very bright nebula that is seen at the one o’clock position “on top of” SH2-161. It is also designated as NGC7538 Northern Lagoon Nebula, is in the constellation Cepheus. It is located about 9,100 light-years from Earth. It is home to the biggest yet discovered protostar which is about 300 times the size of the Solar System. It is located in the Perseus Arm of the Milky Way and is probably part of the Cassiopeia OB2 complex. It is a region of active star formation including several luminous near-IR and far-IR sources. Stars in NGC 7538 are mainly low-mass pre-main-sequence stars.
Messier 52 or M52, the Cassiopeia Salt and Pepper Cluster, is an open cluster of stars in the highly northern constellation of Cassiopeia. It was discovered by Charles Messier in 1774. It can be seen from Earth under a good night sky with binoculars. The brightness of the cluster is influenced by extinction, which is stronger in the southern half. The core of the cluster shows a lack of interstellar matter, which may be due to supernovae explosion(s) early in the cluster’s history.
Distance:
- SH2-157 Lobster Claw Nebula (Californietto Nebula): 11,050 light years
- NGC7635 Bubble Nebula: 11,090 light years
- SH2-161: Distance estimates 2800 pc [1982ApJS…49..183B] or 2800 pc +/- 900 [2003ApJ…598.1005F]. 1 parsec = 3.26156 light years.
- SH2-161: 9133 +/- 2935 light years
- NGC7538 Northern Lagoon Nebula: 9100 light years
- M52 Cassiopeia Salt and Pepper Cluster: 500 light years
Constellation: Cassiopeia & Cepheus (NGC7538)
Designations:
- SH2-157 Lobster Claw Nebula (Californietto Nebula), LBN537
- NGC7635 Bubble Nebula, C11, SH2-162, LBN548, Ced210
- SH2-161, LBN547
- NGC7538 Northern Lagoon Nebula (Brain Nebula – Dreyer’s Object), SH2-158, LBN542, Ced209
- M52 Cassiopeia Salt and Pepper Cluster (October Salt and Pepper Cluster, The Scorpion Cluster), NGC7654, CR455, Mel243
{From https://skyandtelescope.org/online-gallery/sh2-157-lobster-claw-nebula-in-sho-palette/ , https://it.wikipedia.org/wiki/Sh2-157 http://galaxymap.org/cat/view/sharpless/161 https://en.wikipedia.org/wiki/NGC_7538 https://en.wikipedia.org/wiki/Messier_52 and Stellarium}
Capture Notes
SH2-157 Lobster Claw and its neighbors were the first targets for the Southern Cross on our first night at the Comanche National Grasslands Camel Rock camping site during our October dark skies trip.
After a late arrival at the campsite, we set up the camp (first clearing the cactus and large rocks). I didn’t start setting up the AP equipment until about 1800. I finished setting up Big Bertha in the dark and then got the Southern Cross going on its first target.
It was quite windy causing power issues with the Southern Cross, which was connected to the cigarette lighter plug that Paul had installed drawing power from the vehicle’s battery. The connection has never been very secure. I didn’t realize that the wind would have such a deleterious effect on it. When I came out to change Southern Cross targets at about 00:30MDT, I discovered that while the mount was still powered and tracking, the laptop had shut down, thus was not collecting data after 23:08MDT. When I went to reboot it, I got errors that the battery was low and needed to be plugged it…it would not recognize that it was plugged in.
I also discovered when I polar aligned the equipment on the second night, that it was out of alignment more than the settling overnight would account for – so all the images captured during the first night on both rigs have a substantial amount of star trails.
Sequence Plan (5Oct2024): Gain: 158, Temp: -0°C, offset=30. 27x300sec. Total: 135 minutes. 2:15hrs. Captured 5Oct2024, 2051MDT – 5Oct2024, 23:08MDT.
Equipment
Equipment: All equipment controlled by HP Probook running Sequence Generator Pro v4.4.1.1441
- Imaging (ASI2400-SC): ZWO ASI2400MC imaging camera on (Southern Cross) Askar FRA600 108mm f/5.6 Quintuplet Petzval Flat-Field Astrograph
- Autofocuser: ZWO EAF Electronic Automatic Focuser (EAF-5V-STD)
- Mount: Rainbow Astro RST-135E (controlled by iHubo ASCOM driver)
- Polar alignment: QHYCCD camera (controlled by Polemaster for polar alignment)
- Autoguiding: Orion 60mm Multi-Use Guide Scope with Orion StarShoot AutoGuider Pro Mono Astrophotography Camera (controlled by PHD2)
Summary
Captured: 5 October 2024; Total capture: 2:15hrs
Shooting location: Comanche National Grasslands’ Camel Rock
Equipment: Big Bertha on Rainbow Astro RST-300
Processing summary: Captured in SGP, stacked in APP (Adaptive Airy), star removal with Starnet++, processing with LR/PS