Jump to content

  •  

* * * * *

Cosmic Challenge: NGC 147 and NGC 185


Discuss this article in our forums

Cosmic Challenge

NGC 147 and NGC 185

 

November 2018

 

Phil Harrington

 

 

This month's suggested aperture range

Small scopes/Big binoculars

2.8- to 5-inch (70mm to 127mm)

Target

Type

RA

DEC

Constellation

Mag

Size

NGC 147

Galaxy

00 33.2

+48 30.5

Cassiopeia

10.5b

13.2'x7.7'

NGC 185

Galaxy

00 39.0

+48 20.2

Cassiopeia

10.1b

11.9'x10.1'



At last count, the galactic conglomerate known as the Local Group has at least 54 member systems, and probably more, all within 10 million light years. Three spiral galaxies -- the Milky Way, the Andromeda Galaxy M31, and the Triangulum Spiral M33 -- dominate the collection, but a horde of smaller systems are also scattered throughout.  Most of those are dwarf galaxies, either elliptical or spheroidal.

 

Above: Autumn star map from Star Watch by Phil Harrington.

 

 

Above: Finder chart for this month's Cosmic Challenge.

Chart adapted from Cosmic Challenge by Phil Harrington.
Click on the chart to open a printable PDF version in a new window.

 

 

At least 17 of those less massive members are gravitationally bound to M31, creating a system of satellite galaxies.  Two -- M32 and M110 are nice challenges for handheld binoculars.  Most amateurs are familiar with them, since they lie in the same field of view of the parent Andromeda Galaxy.  But two others, designated as NGC 147 and NGC 185, are not as nearly well known.  Both are several degrees to M31's north, across the border in Cassiopeia and feature smaller, fainter disks that are much more challenging to see.

 

To find them, aim your telescope or binoculars exactly halfway between M31 and Shedar [Alpha (α) Cassiopeiae], the brightest star in the Cassiopeia W.  There, you should find a line of three 5th-magnitude stars aligned north-to-south.  Using a low-power eyepiece, focus on the trio's northernmost star, Omicron (ο) Cassiopeiae.  NGC 185 is just 1° west of Omicron, close enough so that both just squeeze into the same field of a 26-mm eyepiece through my 4-inch refractor. NGC 147 is almost exactly 1° further west, so once you find one, you're not far from the other.

 

Let's start with NGC 185, which is the brighter of the pair. NGC 185 was discovered by William Herschel on November 30, 1787.  To see for yourself, first move the glare of Omicron out of view.  That way, NGC 185's slightly elongated disk can be spotted packed inside a triangle of 8th- and 9th-magnitude stars. Although the full extent of this dwarf spheroidal galaxy spans 12'x10' in photographs, the outer boundary is far too faint to be seen visually, at least in this aperture range. Studies indicate that NGC 185 is 2.05 million light years away, about 500,000 light years closer than M31.

 

Bump another degree farther west and you should discover NGC 147. Maybe. Papa Herschel didn't see it when he found NGC 185. That discovery was left to his son, John, who was first to lay eyes on it 42 years later. Although it has almost the same magnitude value as NGC 185, the surface brightness of this dim dwarf is noticeably lower, making it more difficult to pick out.  Again, expect to see a small, dim, featureless blur.  Part of the reason that NGC 147 is more challenging is due to distance. It's actually a little farther away than M31, at an estimated 2.53 million light years.

 

Averted vision will most likely be required to see both challenges, especially NGC 147.  But sometimes, averted vision alone is not enough.  Another way to detect difficult objects is to tap the side of the telescope tube very gently. The eye's peripheral vision is also very sensitive to motion, so slight side-to-side movement will often reveal marginally visible objects, even if only for a moment.

 

Have you ever caught yourself holding your breath as you search for a difficult target through your telescope?  I know that I have.  Oxygen deprivation, even if for only a few seconds, can actually desensitize your eyes, so keep breathing.  In fact, some observers find that by breathing deeply for 10 to 15 seconds before peering into an eyepiece, and continuing to breathe normally once in position, actually accentuates faint objects.

 

Above: A sketch of NGC 147 (left) and NGC 185 through the author's 4-inch (102mm) refractor at 39x.

 

Through backyard telescopes and giant binoculars, both outwardly look the same, save for the difference in surface brightness.  It's not until you probe deeper do you see that they are actually radically different. NGC 147 is pretty much your run-of-the-mill dwarf spheroidal system. Spectral analysis indicates it is comprised of mostly old stars, with the last major spurt of star formation probably taking place more than 3 billion years ago.

 

But look at NGC 185 closely and you'll see that it is active right now. Although most star formation also took place billions of years ago, inside we find clusters of young stars and a surprisingly active galactic nucleus. That has led NGC 185 to be cross-classified as a type II Seyfert galaxy. Although some question that classification, it makes NGC 185 the only Seyfert galaxy in the Local Group.

 

Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my web site or post to this e-column's discussion forum.

 

Remember, half of the fun is the thrill of the chase.  Game on!



About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2017 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.

 


  • Dave Mitsky, okiestarman56, John O'Hara and 5 others like this


4 Comments

Photo
Astrojensen
Nov 04 2018 10:42 AM

These are interesting and woefully underobserved. 

 

NGC 185 isn't that much of a challenge, though, being only slightly fainter than NGC 205/M110 and fairly easily seen with averted vision in my 50/540mm Zeiss achromat at 39x from dark-ish skies (Bortle 3/4, NELM ~6). It is smaller and a little denser than M110.

 

NGC 147, on the other hand... Is MUCH fainter and a hyperfaint, ghostly glow in the 50/540 Zeiss at 39x, requiring excellent conditions to be seen with this aperture reliably. 

 

Both naturally strongly benefit from somewhat more aperture, but they ARE visible in even a 2" glass, if your skies are good enough. NGC 147 is highly sensitive to light pollution, so it may not take much to render it invisible in even a fairly large telescope. Your fine sketch in the article shows the difference between them nicely. 

 

There's a nice little bonus galaxy nearby, on the other side of Omicron Cassiopeiae, NGC 278. It's not a member of the Local Group, but a more distant, highly active, star-forming spiral galaxy. It has very high surface brightness and though much smaller than either NGC 185 or NGC 147 is as easy to see as NGC 185, if not easier. It'll need some more magnification to make it clearly nonstellar, though. 50x or so should do nicely. On photographs the arms are extremely bright, but I've not seen them in even my 12". 

 

 

Clear skies!
Thomas, Denmark

    • Starman1, okiestarman56, CelestronDaddy and 1 other like this

Yep, NGC185 is not that difficult. On good nights, I can see it quite regularly from our light polluted backyard in 63mm Telementor. NGC147 is something else. I was trying to spot it several times from the backyard in the same telescope without luck. I succeeded only with 250mm reflector, or when I took the 63mm refractor under dark skies. In 63mm, this was definitely a challenge, at least for me. It was just very faint ghost glow appearing only for short moments. I started to believe that I really saw the galaxy only when I compared that the observed position angle with the atlas.

 

As for nearby NGC278, it was kind of challenge in 63mm as well. It was invisible up to powers of 84x. Until I plugged in 8mm eyepiece (105x). Then suddenly as a miracle, the galaxy was plainly there. It was surprisingly bright with averted vision, considered the fact that I missed it at smaller magnifications.

 

BTW, there is another nearby satellite of M31, galaxy IC10. This one was quite challenge in 250mm from our backyard, or in 150mm under darker sky.

 

There is another interesting less known object in the area. One night, when searching for NGC147 and NGC185 in Telementor, I run on star group near star omicron Cas (just outside the map in the article). It looked to me like a open cluster,however there was nothing plotted in this position in all my atlases, including Uranometria 2000.0. I was really excited, I was hoping that actually discovered something. After couple of days I identified it with the help of Simbad as open cluster Alessi 1 / Le Drew 1.

    • okiestarman56 and Astrojensen like this
Photo
John O'Hara
Nov 07 2018 07:01 PM

As I read through the article and post, I'm reminded that Phil makes most of these observations from Long Island, NY, and mag. 5 suburban skies on good nights.  So if I'm thinking that I'm doing reasonably well from my astronomy club's Bortle 3-4 skies using my 100 SW ED, I have to keep my pats on the back in check when I remember from where Phil does much of his work.

    • Astrojensen and NYJohn S like this
There is another interesting less known object in the area. One night, when searching for NGC147 and NGC185 in Telementor, I run on star group near star omicron Cas (just outside the map in the article). It looked to me like a open cluster,however there was nothing plotted in this position in all my atlases, including Uranometria 2000.0. I was really excited, I was hoping that actually discovered something. After couple of days I identified it with the help of Simbad as open cluster Alessi 1 / Le Drew 1.

 

Excellent. I have seen that cluster but wasn't able to Identity it.

 

I regularly observe these two galaxies in large scopes on my way to some much fainter galaxies in the region. I'll have to try them in my 15x70s on a parallelogram mount but I'm skeptical I will see them, I am coming to realise cataract surgery is likely on my near future.

 

Jon

    • Sasa likes this


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics