Archive for February 2021

My Quest to Observe the Entire Herschel Catalog: By “Guest Host Larry McHenry” From Pittsburgh

February 18, 2021

It is Done!

As of May 13th, 2020, I have now completed observing all 2,482 identifiable objects of the Herschel 2500 Catalog.

My last catch was ‘H II-840’ a pretty little one-arm galaxy – NGC3978 in the Great Bear – Ursa Major.

The idea for this ‘Herschel Objects’ project started back at the end of 2012, as I was wrapping up a Constellation survey based on the “Night Sky Observers Handbook“. I realized that my observations would already include a large number of the Herschel-400 objects. So after identifying all the ‘400’ objects that I had previously observed, it only took me less than a year to finish the ‘Herschel 400’ list. For this phase of the project, I utilized the Astronomical League’s “Herschel 400 by Constellation” list and their “Observe the Herschel Objects” booklet. I then downloaded the AL’s “Herschel-II” list of the next 400 objects and began hunting those. 

By the fall of 2016, I was down to the last 60 objects and was wondering what my next project should be. Flipping thru some old “Sky & Telescope” magazines, I ran across an article from the August 2012 issue by Rod Mollise on observing the entire Herschel Catalog of 2500 objects using a deep-sky video camera. This was the inspiration (and project), that I needed, as I was already a videoastronomer, so I began a multi-year effort to observe the entire Herschel Catalog.

So today, we’ll discuss what I’ve learned during that journey among the Herschel Objects. Hopefully, when we are done, you will find them as interesting to hunt as I do.

First, a little background on the Herschel’s:

After the Messier List, the Herschel Object’s are the next most observed deep-sky objects. 
Most amateur astronomers know them by their NGC numbers, but they started out as a list created by British amateur astronomer William Herschel and his sister Caroline, two of the greatest astronomers from the ‘Age of Enlightenment’, which marked the birth of modern science.  

From 1782 to 1790, the Herschel’s conducted systematic surveys of the night sky, in search of “deep sky” objects, and discovered over 2500. Herschel used two telescopes for his survey, a “20-foot Reflector”, which had an 18.5” speculum-metal mirror, and later the great “40-foot Reflector” with a 48” mirror.  Most of Herschel’s recorded observations were made using the ’20-foot’ telescope, as the larger ’40-foot’ was cumbersome to use and suffered from tube current distortions.

Herschel’s telescopes didn’t have clock drives to track the stars, so instead, he would point the telescope to the meridian and let the Earth’s rotation carry objects across his field of view while he was up on a ladder observing. William would then call down to Caroline, at the bottom of the telescope, whenever he saw anything interesting, and she would write down his descriptions and time and where the telescope was pointing. Caroline would then quickly read this back to William and he would confirm the observation while the object was still in the eyepiece. This method allowed them to observe and record a nightly east-west strip of sky. The next day, the two of them would use their recorded observation to calculate the objects position on a star atlas. They would then move the telescope’s elevation up or down, in preparation of the next nights survey run.  Using this method, they were eventually able to observe all of the sky visible from England.

The Herschel’s observing technique of surveying, cataloguing, and classifying what they found, and then using that data to try and understand the structure of the universe, has become one of the most important tools of modern astronomy.

How I accomplished the project:

So back in 2016, as I began a multi-year effort to observe the entire Herschel 2500 Catalog, the first thing I needed to do was come up with a list of the Herschel Objects! While during the process of William and Caroline Herschel’s original recording and publishing of their observations from 1786 thru 1802, along with subsequent reprints and revisions over the 19th century, there have been a number of discrepancies over misidentified or non-existent objects. Depending on the source, of the Herschel’s 2500 objects cataloged, there are anywhere from the low 2400’s to over 2500 actual objects. Mark Bratton, in his book “The Complete Guide to the Herschel Objects“, gives a good review of the issues and historical attempts to rectify Herschel’s list of objects. He eventually settles on there being only 2,435 identifiable Herschel Objects. (I utilize his book’s visual descriptions and DSS images to help in comparing and confirming my personal observations). In addition to the above book, I also utilized George Kepple & Glen Sanner’s “Night Sky Observers Guide Handbook” and internet resources ‘WIKISKY‘ and ‘The NGC/IC Project’ to validate my observations. 

To help tackle this project, I downloaded several lists from various websites, and after combining, distilling, and sorting, I generated a personal spreadsheet/logbook to help in my tracking & logging. The core data for my logbook comes from a list of 2,482 Herschel Objects by Steve Gottlieb. 


All of my Herschel Object observations can be found in their individual constellations in my website under my ‘Constellation Tour’ page. To see the entire list together, I’ve created a specific page for the Herschel Project: “Herschel Tour”  

http://www.stellar-journeys.org/herschel-tour.htm


Over the course of this project, I have spent a total of 239 nights working my way thru observing all of the Herschel Objects. 

Even though I really didn’t get serious about completing the list until 2012, my observations stretch all the way back to 1984. 

All of the early observations are visual sketches, (78 objects), made at the telescope eyepiece, with everything after 2001 using videoastronomy (EAA) short-exposure lucky imaging technique. I eventually used a total of ten different telescopes for this project. Six visually – 80mm f3.2 refractor, 8″ f4.5 dob, 10″ f5.6 dob, 13.1″ f4.5 dob, and a 8″ & 12″ SCT at f10. The dobs and small refractor were manual telescopes, with the two SCT’s being motorized, but all required using star-charts and star-hopping techniques to locate the objects. 

For the videoastronomy observations, I used four telescopes – 50mm f3 refractor, 80mm f6 refractor, 6″ RC at f9, f6.3 & f5, and a 8″ SCT at f10, f6.3 & f3.3.  All these telescopes were on either SCT or CGEM mounts that could track and later utilize GOTO.

The cameras used were a StellaCam-EX (2.5 seconds exposure), StellaCam-II (8 seconds exp), a Samsung SDC435 (8 seconds exp), a peltier cooled, wireless controlled StellaCam-3 (unlimited exp), and finally a ZWO ASI294MC Pro camera used in EAA mode (generally for around 120 second exposure). 

While I prefer going to dark sky locations, such as Pennsylvania’s Cherry Springs State Park, for my observing, utilizing near-realtime deep-sky videoastronomy cameras has allowed me to pull in faint 14th magnitude plus galaxies not visually possible from my backyard observatory located within 10 miles of downtown Pittsburgh, PA. This greatly expanded the number of clear evenings available for working on this project. 

Having spent time over the past several years following in the Herschel’s tracks, you could begin to pick-up on how they were doing their observing run for that particular night back in the 1780’s, slowly letting the Earth’s rotation bring each object into their sweep. Using today’s modern equipment, there’s no need to wait; all you had to do was hop down the sweep path to the next observable object. When you think about that, it’s sort of inspiring to think that in your own way you are following in their footsteps!

In retrospect, I have learned a lot about the lives of William and Caroline Herschel, along with the objects that they discovered. While there are a number of nice large, bright objects including galaxies, star clusters, and nebula, the majority of Herschel’s objects are small, faint, dim smudges of galaxies. It gives you an appreciation for the brighter Messier Objects. Still, there is a wide variety of shapes and sizes of interesting deep sky objects for any type of telescope. I now have a much greater respect for all those faint fuzzies and the work of the Herschel’s! So I encourage everyone to get out tonight and try your hand at finding and observing the deep-sky objects of William and Caroline Herschel!!

An examples of my many sketches:

My equipment used for this project: Telescopes, observatory and camper : Larry McHenry, Pittsburgh, Pa


Hope you enjoyed my story: Larry McHenry

Herschel 400 Notes: By “Guest Host Sue French” From New York

February 16, 2021

Sue and Alan French

Click on to enlarge: The latest Herschel 400 book (above) from the Astronomical League. Consider ordering your copy today.

NGC 1893 Open Cluster + IC 410 Emission Nebula – February 2021 Observer’s Challenge Report – Auriga #145

February 5, 2021

MONTHLY OBSERVER’S CHALLENGE

Compiled by:

Roger Ivester, North Carolina

&

Sue French, New York

February 2021

Report #145

IC 1893 and IC 410, Cluster and Emission Nebula in Auriga

Sharing Observations and Bringing Amateur Astronomers Together

Introduction

The purpose of the Observer’s Challenge is to encourage the pursuit of visual observing. It’s open to everyone who’s interested, and if you’re able to contribute notes and/or drawings, we’ll be happy to include them in our monthly summary. Visual astronomy depends on what’s seen through the eyepiece. Not only does it satisfy an innate curiosity, but it allows the visual observer to discover the beauty and the wonderment of the night sky. Before photography, all observations depended on what astronomers saw in the eyepiece, and how they recorded their observations. This was done through notes and drawings, and that’s the tradition we’re stressing in the Observer’s Challenge. And for folks with an interest in astrophotography, your digital images and notes are just as welcome. The hope is that you’ll read through these reports and become inspired to take more time at the eyepiece, study each object, and look for those subtle details that you might never have noticed before.

This month’s target

John Herschel discovered the open cluster IC 1893 in 1827 with the 18¼-inch reflector at Slough in Buckinghamshire, England. His handwritten journal reads: “Rich, coarse, scattered and straggling. It more than fills the field. The stars are 9…15 magnitude.”  The engulfing nebula, IC 410, wasn’t discovered until 1892, when Max Wolf found some new extended nebulae on photographic plates taken with a 6-inch Voigtländer portrait lens. My paraphrased translation of the pertinent section of his discovery says: The ribbon-rich nebula shown on the plates around the star cluster surrounds the star BD+33 1023 [HD 242908] should also be new. It largely encloses the whole group.

The nebula is roughly 11,000 to 12,000 light-years distant, and the adolescent cluster within it is at least 4-million years old.

Mario Motta: Observer from Massachusetts

Went deep in this, two nights, 2.5 hours Halpha, 1 hour O3, 1 Hours S2, total about 4.5 hours. Actually took over 6 hours of subs but the first night had gusty winds so had to drop many less than optimal sub frames. I used the hubble palate on this, it has a very strong oxygen component, why it has the blue nebula background. The star cluster NGC893 is 4 million years old, and my guess is it must have had one or more supernovae to account for the oxygen and sulphur in the nebula. This is 12,000 LY’s away. The remarkable “tadpoles” to the northeast (left in the image) are bok globules being radiated away by the star cluster’s hot stars, likely some star formation going on within them. This nebula would also make a very nice wide field object. However, I will leave that for another and stay with my 32-inch detail imaging.  And I continue to stay one month ahead

Roger Ivester: Observer from North Carolina

NGC 1893 open cluster and emission nebula IC 410 in Auriga 

Dates: January 9th, 12, and 14th

Telescopes:  10 and 6-inch reflectors 

Sketch:  6-inch reflector 

Sketch Magnification:  35x – 2.0º Field of View 

Using my 10-inch, I was able to observe the faint and small open cluster, NGC 1893, on three different nights during January.  At 136x, I could count at least 50 faint stars, with an overall triangular shape.  This cluster also contains a couple nice pairs of double stars.  A faint cluster for sure that can be difficult to locate, due in-part to being located in a very rich star field.  

However, I was unable to see the faint surrounding nebula, IC 410, with the 10-inch, despite using various magnifications, including 36x, and several hours over the three night period.  I did try a UHC filter, but without any success.         

On my 3rd night, I chose to also use my 6-inch f/6 reflector at a magnification of 35x, with a 2º field of view.  I was observing from my moderately light polluted back yard with a NELM of about 5.0 on this night.  

I was able to see some faint nebulosity enveloping the cluster, after continuous crossings over the cluster and repeating, using the RA slow-motion control on my equatorial mount.  After more than an hour on this night, the nebula became visible, appearing as an extremely faint haze surrounding the cluster.  

I was very pleased. After three nights of searching and observations dating back to January 1994, I had finally seen IC 410.  I felt a great sense of accomplishment.  For the visual observer, nothing can be more rewarding than after many nights of failure, and then finally seeing a very faint deep-sky object.

Amateur astronomy is not just observing the showpiece objects, but often times, the greatest satisfaction can be “finally” seeing the faintest of deep-sky objects.

There have been many other deep-sky objects, that took multiple observations over a period of years to see. A few examples would be: The companion to Sirius, the fifth component of the Virgo Diamond, and NGC 6822, known as Barnard’s Galaxy, just to name a few. It was only after reading that many observers found the best view of NGC 6822 when using a small refractor.

From Burnham’s Celestial Handbook: “Hubble found it (NGC 6822) “fairly conspicuous” in a short focus 4-inch finder with a low-power ocular, but “barely discernible at the primary focus of the 100-inch”.

So, in September 2014, I used my 102mm refractor, rather than my 10-inch reflector and saw (NGC 6822) almost immediately from my back yard, despite unshielded streetlights being in close proximity. This galaxy deserves a dark sky, with excellent transparency.

The following is my pencil sketch of NGC 1893 and IC 410, using a blank 5 x 8 notecard, with a 3-inch circle and the colors inverted.

Glenn Chaple: Observer from Massachusetts

This month’s Observer’s Challenge takes us to the emission nebula IC 410 and its embedded open cluster NGC 1893. The cluster is comprised of several dozen members, some twenty of which are magnitude 9 to 12. Most are massive O and B-type stars. They appear relatively faint because the entire system is 12,000 light years away.

It’s the surrounding nebulosity that provides the real challenge. A haze surrounding NGC 1893 might be glimpsed with 6 or 8 inch scopes from remote dark-sky locations, but observers working from typical suburban environments will need as much as twice that aperture and possibly an assist from an O-III filter.

A distinctive feature of IC 410 is a pair of gaseous streamers northeast of NGC 1893 that point away from the cluster. Their similarity in appearance to larval frogs gives IC 410 the nick-name the “Tadpoles Nebula.” They appear in the accompanying close-up image of IC 410 taken by ATMoB member Mario Motta. For an ultimate Observer’s Challenge, see if you can spot them visually.

Located at RA 5h 22.7m and dec +33°24’, this cluster/nebula complex is a quick star-hop from Melotte 31, a stellar group that includes the 5th magnitude star 16 Aurigae. About 20 arc-minutes west of 16 is the near-twin double star Struve 666 (magnitudes 7.85 and 7.89, separation 3.2”). Before moving on to NGC 1893/IC 410, give this little gem a look-see.

Larry McHenry: Observer from Pennsylvania

NGC1893/IC410 is located in the winter constellation of Auriga – ‘The Charioteer’.

This 7.5 magnitude deep-sky object is a moderate-rich open star cluster embedded within a faint ionized HII emission nebula making up the core of the Auriga OB2 association. An OB association is a large, very loose form of an open star cluster consisting of young spectral type “O” and “B” stars.

While OB associations are considered a separate Deep-Sky category from open clusters, both types can be found together, with an open cluster forming the core region of a larger OB association. Visually, OB associations are great binocular and rich-field telescope objects. I have a number of OB association finder charts and sketches on my webpage: http://www.stellar-journeys.org/OB-Tour.htm

Within Auriga OB2, the star cluster NGC1893, also cataloged as Collinder-63 and Melotte-33, contains a  visually elongated mix of around two dozen medium-brightness stars and another several dozen fainter stars, with many more visible in images. It is about 12,400 light years distant with a diameter of around 70 Ly, and around 3 million years old. 

The nebula, IC410, (also cataloged as SH2-236), nicknamed the “Tadpole” covers around 100 light-years in diameter. It is faint visually, though enhanced by UHC filters, but prominent in narrowband imaging.

The two bright cometary nebula globules that give IC410 its name, located to the north of the cluster center, are Simeis-129 and 130 (the brighter of the two). Both are about 10 Ly in length with their shapes eroded from the main nebula by stellar winds and radiation from the nearby young star cluster.

Video-Capture:  NGC1893

09/05/2013 from Cherry Springs State Park, Pa. at the Black Forest Star Party, using a 6-inch RC optical tube @ f/5 on a GEM mount, using an analog video-camera & IR filter @ 15 seconds, unguided single exposure.

 Visual Screen Sketch:

NGC 1893 and IC 410

01/09/2021 – 8-inch SCT f/6.3 GEM mount, CMOS/USB color camera & Ha/OIII/H-beta narrowband filter, 60 second exposure. Open cluster and emission nebula. 

Image:    NGC1893/IC410

01/09/2021 from Big Woodchuck Observatory backyard in Pittsburgh, PA.

Using an 8-inch SCT optical tube @ f/6.3 on a GEM mount, with a CMOS/USB color camera and Ha/OIII/H-beta narrowband filter @ 60-second guided exposure live stacked for 30 minutes.

North is to the right and west is down or toward the bottom.

James Dire: Observer from Illinois

NGC1893 is an open star cluster surrounded by an emission nebula IC410. The complex is located in Auriga five degrees north of the star Elnath (mag. 1.67) and five and one-third degrees east of the star Hassaleh (mag. 2.68). The cluster is about 25 arc minutes in diameter while the nebula is roughly 40 x 30 arc minutes in size. They lie approximately 12,000 light years away. Visually the cluster is magnitude 7.5. The nebula is drastically fainter. I have never seen it in a telescope…but have captured it on images.

NGC1893 was discovered by John Herschel in 1827. IC410 was discovered by the German astronomer Maximilian Franz Joseph Cornelius Wolf of the University of Heidelberg. He found the nebula on a photographic plate on September 25, 1892.

NGC1893 is a relatively young cluster. The cluster is forming massive O and B stars whose radiation excites the gases in IC410. A study of the cluster by Maheswar et. al in 2007 [Mon. Not. R. Astron. Soc. 379, 1237–1247 (20070] found five O-type stars whose ages were estimated to be between 2 and 4 million years old. A study of NGC1893 by Xue et al. in 2019 [Mon Not R Astron Soc (2019) 482 (1): 658-697] found 147 variable stars in the cluster including 15 eclipsing binaries. While the NGc1893 appears as a loose galactic star cluster in amateur telescopes, it is estimated to contain between 4000-5000 formed stars, with more on the way.

My image of NGC1893 and IC 410 was taken with a 190mm f/5.3 Maksutov-Newtonian telescope using and SBIG ST-2000XCM CCD camera. The exposure was 6.5 hours using 10-minute subframes taken over three nights. In the image, north is up and east to the left. IC410 looks a lot like the Rosette Nebula in Monoceros, although it is not as close, large, or bright.

The brightest star in the image is the double-star on the right edge, HD34760 shining at magnitude 8.32. The two components are magnitude 8.9 and 9.6 and are separated by 15 arc seconds. The next brightest star is HD242908 located just north of the center (dark hole) of the nebula. There is a bright patch in the nebula located northeast (upper left) of the center of NGC1893. This region is the only part of the nebulae that can be easily captured in an eight-inch telescope. The faintest stars in the image are magnitude 19!

Barry Yomtov: Observer from Massachusetts

With our uncooperative weather here in New England, I have not been able to get any imaging done this month. So my image of IC 410/ NGC 1893 for the February object of the month was actually taken in November and December of 2016.

My image processing skills with PixInsight having significantly improved since 2016, so I decided to reprocess the image data, so it’s like a brand new 2021 image.  

The equipment I used during the 2016 session was actually my initial set up was with fast optics; a 9.25-inch Schmidt-Cassegrain with a Hyperstar 3 lens providing f/2.3 speed. I was imaging with DSLRs at that time: Canon DSLR 60Da for RGB color images, and a Baader filter modification to a Canon T4i  for all Ha (12 nm) narrow band images.  In reviewing my notes in my log, the RGB component (60Da) was taken at ISO1600, 30 images at 25 sec/exposure (13 minutes). The Ha 12 nm narrow band images were taken over 3 evenings; ISO1600, 82 images at 75 sec for 102 minutes total exposure.  

With my improved processing with PixInsight and still applying PhotoShop, I was able to bring out greater detail of the Tadpoles. I’ve also included the Ha  image in gray-scale, as it enhances the surrounding nebulocity in this wide field image.

Joseph Rothchild: Observer from Massachusetts

The weather has been poor recently, but I was able to observe the February object (NGC 1893 and IC410) on January 7th.  I observed with my 10″ reflector on Cape Cod.  This was a new deep-sky object for me.
This object was easily located in Auriga near a row of 3 stars: 17, 18, 19 Aurigae.  There was an arc of 10 stars in the cluster with a faint nebulosity.  There was also a group of 4 stars in the shape of a rhombus.  Best viewing was with a 14 mm eyepiece at 102x.  The nebulosity was slightly more visible with a narrow band pass (NBP) filter.

Anas Sawallha: Observer from Jordan

This nebula is embedded in a very dense star field, which made it difficult to draw all the stars in the NGC 1893 field, especially using a manual Dobsonian. I’m not quite sure about my sketch, but the following sketch is my result. I would like to have another go at it, but the weather has not been good.

Telescope: 10-inch Newtonian Reflector

Focal length: 1200mm

Eyepiece: Aspheric 25mm

Seeing: II

Location: Al Kharaneh palace (Mwaqqar) 

Bortle: up to date 4

Gregory Brannon: Observer from North Carolina

The Moon was a bright waxing Gibbous, which made it hard to see even Messier 38, which is typically plenty bright enough to see. I had made a list of several clusters in the region to look for, informed by star maps and Skiff & Luginbul’s handbook, but through ergonomics concerns and a moon-polluted sky, I ended up giving up after seeing just M38 and NGC 1893.

Notes from 2021 February 24th in the evening:
NGC 1893 – 10-inch f/5, 10mm Plossl (120x), 52° AFOVA faintly dim grouping of stars, hard to tell apart from the field stars. Forms two groups, sort of connected by a very tenuous bridge of three dim stars (at 48x; the bridge seems to have disappeared at 120x)

Really tough to pull NGC 1893 out from the star field at 48x with the bright moon, but somewhat distinct at 120x.

Finderscope: 8×50 (mirror diagonal): demonstrating that it’s sort of at the center of a bright arching asterism which I use to find M38.