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Cosmic Challenge: The Southern Pinwheel


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Cosmic Challenge: The Southern Pinwheel

 

November 2021

Phil Harrington

This month's suggested aperture range:

Giant Binoculars,
3- to 5-inch (75-127mm) telescopes

 

 

 

Target

Type

RA

DEC

Constellation

Magnitude

Size

NGC 300

Galaxy

00h 54.9m

-37° 41.0'

Sculptor

9

22'x16'

 

 

Have you ever heard of NGC 300, the Southern Pinwheel Galaxy? Were it positioned high in our autumn sky in a prominent constellation, you certainly would have. In fact, NGC 300, an Sc spiral tilted nearly face-on to our view, would be one of the season's showpieces, especially through large backyard telescopes. Because it lies in the far southern sky, nestled among the faint stars of Sculptor, it remains the purview of diehard deep-sky fanatics only.

 

Above: Evening star map showing the location of this month's Cosmic Challenge.

 

Credit: Map adapted from Star Watch by Phil Harrington

 

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

 

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

 

 

NGC 300 presents an interesting challenge for more than one reason. First, yes, its position in unfamiliar terrain makes it difficult for star-hoppers. The brightest star in the area, Ankaa [Alpha (α) Phoenicis], shines only at magnitude 2.4 and is not on anyone's "wow, look at that" list. Therefore, the first challenge to finding NGC 300 is finding Ankaa, our star-hop's starting point. I always begin about 55° to its north, at the Great Square of Pegasus. Extend the eastern side of the square, from Alpheratz [Alpha (α) Pegasi] to Algenib [Gamma (γ) Pegasi], straight south for 34° to 2nd-magnitude Deneb Kaitos [Beta (β) Ceti], and then for another 25° southward to Ankaa. Binoculars will help to trace the route. Once there, shift your finderscope's aim 5°, or about one field, northeast to the wide pair of 6th-magnitude stars Lambda-1 and -2 (λ-1 and λ-2) Sculptoris. NGC 300 is just 2° to their east-northeast.

 

Even when you are aimed exactly at it, NGC 300 remains a demanding target because of its very low surface brightness. Like two other difficult objects, M33 in Triangulum and M74 in Pisces, the light from NGC 300's S-shaped spiral arms softly diffuses away from a nearly stellar core. As a result, even though it is typically rated at 8th magnitude, NGC 300's surface brightness plummets to nearly 14th. On one hand, the large apparent size of NGC 300's spiral disk means that a low-power eyepiece is best for segregating the galaxy from its surroundings. On the other hand, low-power eyepieces and their proportionally large exit pupils typically lower the contrast of an object and the surrounding sky. If the target's surface brightness is low to begin with, well, you can see where this is going.

 

To see for myself what combination would be best for spotting NGC 300, I set up my 4.5-inch (10.8 cm) f/4 reflector. Armed with several eyepieces ranging in focal from 5 to 26 mm, I aimed toward the galaxy and took a look. Going back and forth between eyepieces, I found the most aesthetically pleasing view came at 38x and is captured in the rendering here. The field was large enough to take in the dim glow of the galaxy as well as reveal three of the Milky Way stars floating in front. The galaxy's dim oval disk could be seen with averted vision, but looking directly at it caused it to vanish, save for the faint glow of its central core. Higher magnifications caused the galaxy is disappear from view entirely.

 

Above: The view of NGC 300 through the author's 4.25-inch (10.8cm) f/4 reflector.

Below: Color-composite image of the nearby spiral galaxy NGC 300 and the surrounding sky field, obtained in 1999 and 2000 with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory. Credit: ESO

 

 

The foreground stars misled early observers into thinking they were looking at a distant star cluster. In fact, the galaxy's discoverer, James Dunlop, described his find in his 1827 compilation A Catalogue of Nebulae and Clusters of Stars in the Southern Hemisphere as a large, faint nebula that was "easily resolvable into exceedingly minute stars, with four or five stars of more considerable magnitude." Seven years later, John Herschel, who is sometimes incorrectly credited with NGC 300's discovery, also saw "several centres of condensation." Some of those are the field stars noted above, but NGC 300 is also home to several hydrogen-II regions sprinkled across its disk. The most prominent are found just south of the galactic core as well as near the northwestern edge of the spiral disk.

 

Most references place NGC 300 in the Sculptor Group of Galaxies, thought to be some 4 million light years away. Some recent studies, however, cast doubt on this. Instead, these suggest that it is actually be a member of the Milky Way's Local Group. If so, then it is considerably closer to home.

 

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 challenge.  Contact me through my website or post to this month's discussion forum.

 

Until next month, remember that 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 2021 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.

 


  • okiestarman56, John O'Hara, Knasal and 1 other like this


10 Comments

I hadn't heard much about this Galaxy.  If I get a good clear night I'll see if I can see it with my 8" SCT.  From my viewing location, it will only get up to a maximum of 13 deg above the Southern horizon, which for me is pretty light-polluted due to the large city in that direction.  Thanks for posting a great challenge Phil!

    • PhilH and DAG792 like this

Fascinating history on this object.  Looking forward to chasing it as soon as I can get to a site with a better southern horizon.  

    • PhilH and Eclipsed like this

A personal favourite! 
That section of sky is my happy hunting ground; it’s in the darkest part (south), and passes overhead.
The whole area is chock full of galaxies. 

The main problem for this one for most mid latitude northern observers is its low declination.  It is a "tree dodger" at most of my observing sites, reaching only about 15 degrees above the horizon.   This severely limits the observation window and means I am most often observing it between breaks in trees.   It would be much more challenging much above 40 N.  

 

At such a low declination, the background sky is bright and washed out most places I observe, even if a decent Bortle 3 at altitude.  While it isn't hard to find, only the most transparent nights will yield a good look because of the weak contrast.   I never feel like I am really seeing it the way it was meant to be seen and look forward to trying it from the Southern Hemisphere some day.    

 

This galaxy makes for an interesting comparison with NGC 247 about 17 degrees to the north.  247 has substantially worse surface brightness, but is just far enough north that the contrast loss ends up being similar.   (NGC 247 has Burbidge's chain.)  

 

The way I typically do the hop is the form of a grand tour:  NGC 247, then NGC 253 (spectacular), NGC 288 (large globular), Sculptor Dwarf (very low surface brightness), then NGC 300.  I finish up with NGC 55 which is about 1.5 degrees further south and a number of degrees further west.   These are all high value targets in their own right, but each with different character, hampered only by their low positions.  

This is certainly a tough one for those of us in more Northern locations!

 

I had two attempts to look for this target on Nov 6th and 7th.  Both evenings were crisp and cool and fairly clear, with decent seeing for my backyard viewing location.  On the first night I could not even find it with my Celestron Evo 8.  On the second night I did locate it but it was so low and inside a bright dome of light from the city south of my home, it was only barely distinguishable using low power eyepieces (APM 30mm was best) . At that time it hadn't reached its maximum elevation of 13 degrees (at maximum, due South it would have been blocked by trees). I used a filter to try and cut the unwanted light out, however it wasn't much help as it also cut out a fair amount of the galaxy light.  Then I tried to capture and image with my ZWO ASI178MC camera attached but it was so poorly defined that i'm not even going to post the image here!!  Part of the issue is that its a fairly large target for my set up.  I may have another go if conditions are just righ.!  Good luck to those who are attempting to find the target!

I've been up at our place in the high desert for the past week and I've looked at NGC300 each night for maybe 20 -30 minutes. I'm using either 16 or the 22. XI see a little more each night but as Red said it's low on the horizon, about 18° for me. I have a clear southern horizon but there's sky glow some small villages across the border in Mexico.

 

I'm seeing spiral structure but I'm always thinking, "If in were just 10° further south.."

 

Another nice galaxy the region is NGC134. It's a nice mag 10.3 spiral with the mag 13.1 NGC131 as a companion.

 

Jon

    • dave253 likes this

I've seen NGC 300 mentioned as a companion with NGC 55, but never as a member of the Local Group (stated in the article).  Any references?

 

The galaxy is visible in my 15x50 IS binoculars from Northern California as a relatively large, very low surface brightness hazy region, roughly 15' in size.  A star is superimposed on the SW side.

 

I had an excellent view through a 25" f/5 from Australia with the galaxy high overhead.  Using 187x I logged it as bright, extremely large, irregular, elongated roughly 5:3 WNW-ESE, at least 15'x9'.  Contains a large, brighter core region with a mag 11.5 star at the ENE edge of the core.  A mag 9.6 star is in the halo (along a faint spiral arm), 2.6' SW of center and a mag 10.6 star is superimposed in the outer halo, 5.3' SE of center.

 

Spiral structure was surprisingly subtle.  A low contrast, broad inner arm extends west from the north side of the core, curls south on the west side and spreads out.  A more obvious inner arm emerges from the south side of the core and sweeps east and north, though the root of the arm is not defined.  The arm passes through a relatively bright and large HII patch/OB association, ~25" diameter, situated 3.9' E of center and loses contrast further north.   A mag 11.5 star is 2.3' further NE in the outer halo of the galaxy. I didn't have time to examine the galaxy at higher power to search for additional H II knots.

    • Dave Mitsky, Jon Isaacs, dave253 and 1 other like this

Time to get out the chainsaw!

Photo
John O'Hara
Nov 30 2021 11:33 AM

Phil,

 

Kelly and I are wintering in Quartzsite, AZ and I'm hoping to try for NGC 300 tonight with my 100ED f/9 refractor.  This galaxy will be 8 degrees higher down her than in Northwest Pennsylvania, so I'm hoping for a good view.  If things work out, I'll probably bring down a bigger scope next year.

 

John

Photo
John O'Hara
Dec 01 2021 07:28 PM

We'll, I'm a day late and a dollar short as Phil has already introduced December's article.  For what it's worth, I did observe NGC 300 last night from a dark site in the KOFA Wildlife Refuge south of Quartzite, AZ.  It was a decent night, with transparency ranging from 7 to 8 out of 10.  What's more, the object was 8 degrees higher than it would have been from my native area in Northern Pennsylvania.  I found the object at 30x in my 100 mm f/9 refractor.  I then increased the power to 69x and found that this dimmed the image too much.  Decreasing to 45x provided the best view.  I could see it with direct vision, but averted vision revealed a round uniform glow about 20' diameter.  A "bright" field star was on the NE edge, and two other faint stars were superimposed, winking on and off with averted vision as the seeing came and went.  It made me wish that I'd brought a larger telescope to Arizona, but cargo space was limited. 

 

John

    • Jon Isaacs and PhilH like this


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