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Cosmic Challenge: NGC 1360


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Cosmic Challenge:
NGC 1360

December 2020

 

Phil Harrington

 

This month's suggested aperture range:

Giant binoculars and small telescopes

 

Target

Type

RA

DEC

Const.

Mag

Size

NGC 1360

Planetary nebula

03h 33.3m

-25° 52.2

Fornax

9.6p

6.4'


Many stargazers consider Fornax, the Furnace, to be a constellation of the deep south, and therefore, invisible from mid-northern latitudes. While it is true that Fornax scrapes the southern horizon on early winter evenings, it does so at much the same altitude as Scorpius does during the summer. If you can see Scorpius from your observing site in July, you can see Fornax tonight. Assuming it's clear, of course!

Above: Evening star map. Credit: Map adapted from Star Watch by Phil Harrington.

Above: Finder chart for this month's Cosmic Challenge. Credit: Chart adapted from Cosmic Challenge: The Ultimate Observing List for Amateurs by Phil Harrington.
Click on the chart to open a printable PDF version.

 

 

The real reason so few of us take notice of Fornax is not because of its southerly location, but rather its lack of luster. The constellation's brightest star, Alpha (α) Fornacis, shines at a relatively dim magnitude 3.9. The two other primary stars that contribute to the constellation's formal pattern, Beta (β) and Nu (ν) Fornacis, are both below 4th magnitude. To most of us, those few dim stars are not much to look at, but to the inventive eye of Nicolas Louis de Lacaille, they formed a furnace. Lacaille's furnace was not the type you would use to heat your house, however. To him, this was Fornax Chemica, a small heating unit used by the chemists of his day to heat chemicals during experiments.

 

Admittedly, the furnace may not look so hot to naked-eye stargazers. It does, however, hold many amazing deep-sky sights, including one of the most unusual planetary nebulae in the sky. Shortly after it was discovered in 1857 by the American comet hunter Lewis Swift, that nebula, NGC 1360, became an object of mystery and intrigue to those trying to classify it. Some suggested it was an unusual emission nebula, while others felt it was a planetary nebula. Even after decisive studies were conducted in the 1940s by Rudolph Minkowski at Mount Wilson Observatory in California, many still found it a curiosity.

 

Part of that curiosity likely stemmed from NGC 1360's odd appearance. The internal structure displayed by most planetary nebulae is the result of strong, swirling streams of charged particles from their embedded white dwarf progenitor stars. These stellar winds hollow out the central portion of the nebula and create denser outer levels, or shells.

 

Above: NGC 1360. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona via Wikimedia Commons

 

 

NGC 1360 does not show a characteristic central void. Instead, it appears all mixed up, as evident in the image above. The October 2004 issue of the Astronomical Journal included a paper entitled Physical Structure of Planetary Nebulae. III. The Large and Evolved NGC 1360 that reported on the research results conducted by Daniel Goldman and his colleagues of the Department of Astronomy, University of Illinois at Urbana-Champaign. Their studies found that: 

 

There exist planetary nebulae that do not possess morphological features that suggest the presence of wind-wind interactions. NGC 1360 is such a planetary nebula. Its surface brightness does not dip deeply at the center or rise steeply at the limb to indicate a hollow-shell structure.

 

They concluded that the lack of a sharp internal edge to NGC 1360 is due to the absence of fast stellar winds. 

 

A later study, The Planetary Nebula NGC 1360: A Test Case of Magnetic Collimation and Evolution after the Fast Wind, published in the March 20, 2008 Astrophysical Journal by M. T. Garcia-Diaz and others from the Instituto de Astronomia, Universidad Nacional Autonoma de Mexico concluded that the "fast stellar wind from the central star [in NGC 1360] has died away at least a few thousand years ago and a back-filling process has modified its structure producing a smooth, nearly featureless and elongated high excitation nebula."

 

One reason for this appearance undoubtedly has to do with the central stars.  That's right, starS. The central star had been suspected to be binary as far back as 1977, but it took 40 years to finally prove it.  A study made with the Southern African Large Telescope (SALT) and published in January 2018 entitled SALT HRS discovery of a long-period double-degenerate binary in the planetary nebula NGC 1360 (Monthly Notices of the Royal Astronomical Society. 473 (2): 2275) confirmed that the odd binary system consists of low-mass O-type star and a white dwarf. As the study noted, "Around 50 short-period binary central stars (periods ~ 1 day) are known, but only four with measured orbital periods over 10 days" are known. The binary system in NGC 1360 shows an orbital period of 142 days.

 

Clearly, these discoveries will continue to intrigue stellar astronomers, just as they intrigue us, if for different reasons. While NGC 1360 is bright enough to be seen through large binoculars and small telescopes with relative ease, pinpointing its location in the emptiness of the early winter sky can be difficult. Therefore, our challenge is not to understand why NGC 1360 looks like it does. Our challenge is to find this unusual egg-shaped cloud in the first place.

 

Of course, one way to overcome this challenge is simply to use a Go-To telescope. Punch in "NGC 1360" and you're there without any fuss or muss. But what challenge is there in that? Therefore, I challenge you to find NGC 1360 without any aid whatsoever save for your finderscope and a star atlas; that is, a star atlas other than the second edition of Sky Atlas 2000.0. NGC 1360 was omitted from chart #18, where it should be plotted.  But don't worry, we'll find it together.

 

I prefer to start at Lepus, the Hare, just south of mighty Orion. Extend a line from Delta (δ) to Epsilon (ε) Leporis and follow it toward the west for about 17°. Through your finderscope or binoculars, look for a trapezoidal pattern formed from Tau-6 (τ6), Tau-7 (τ7), Tau-8 (τ8), and Tau-9 (τ9) Eridani. Once there, extend a line from Tau-9 through Tau-8, continuing for about 4° westward to a close-set pair of 6th-magnitude stars, SAO 168612 and SAO 168648. NGC 1360 lies just south of the halfway point between those two stars. In fact, all three may just squeeze into a low-power field.

 

Keep in mind that you are not looking for a small disk of light, but rather a large glowing cloud. To put things in perspective, the largest, brightest planetary nebula north of the celestial equator is M27, the Dumbbell Nebula in Vulpecula. M27 shines at magnitude 7.4 and measures 8'x6'. By contrast, NGC 1360 spans 9'x5', nearly identical in apparent size. At 9th magnitude, however, it is also four times fainter.

Above:  NGC 1360 as seen through the author's 10-inch (25cm) reflector.

 


Through my 4-inch refractor, NGC 1360 looks like an unusually symmetrical oval cloud of faintly greenish light resembling a cosmic egg -- hence it's nickname, the Robin's Egg Nebula. The central star, shining at 11th magnitude, is just visible in this aperture, but is quite prominent in larger instruments. It's clear in my 10-inch (25cm) Newtonian. At first glance, the cloud will look perfectly uniform. Take a closer look, however, and a very subtle, almost spiral-like structure becomes evident. A narrowband filter helps to bring this out, but unless the eye is trained to spot delicate details -- a talent only gained by years of experience -- then this will probably pass undetected.

Good luck! And be sure to post your results in this column'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, including Cosmic Challenge: The Ultimate Observing List for Amateurs.  Visit www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2020 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.

 


  • square_peg, Jon Isaacs, John O'Hara and 4 others like this


9 Comments

Excellent post.  I finally have two clear nights tonight and tomorrow but have a 97% illuminated moon tonight.  At 10 deg it is low, but I might be able to snag it.

    • PhilH likes this

This was my hardest starhop to date, with no finder, a 91% illuminated moon and at 10 deg above the horizon.

 

I spent about an hour trying to find it, and only getting a glimpse of it with my 5" apo and 6.5 morpheus.  I tried to bump up the power to 234x and I just missed it in the fov somehow by being off.  I called it quits as I was 2.5 hours in at -5C and getting cold.

 

I only got a glimpse of the robin's egg color.  I hope to revisit it again here soon. 

    • Jon Isaacs, PhilH and msmithmitsky like this

YOU'VE GOT TO HAND IT TO HIM.  PHIL HARRINGTON IS THE ULTIMATE AMATEUR.

    • PhilH and msmithmitsky like this
Photo
msmithmitsky
Dec 07 2020 02:55 AM

Most enjoyable post.  You make it easy and interesting to learn.

    • PhilH likes this

Excellent post, thanks Phil. I still remember a night almost 10 years ago when I chased NGC1360 for the first time. When starhopping to the nebula I visited with my 80mm refractor several interesting targets. The night was very enjoyable, and thanks to this, I decided to write reports on interesting sessions to keep them in memory. This first report can be found here:

 

 https://www.fzu.cz/~...111229_AS80.pdf

    • PhilH likes this
Photo
Stargazer3236
Dec 17 2020 08:32 AM

I have imaged this nebula one time and attempted it many times. My result came out pretty good, using a Nexstar 8SE, ZEQ25 mount, ASI294MC camera, Sharpcap 3.2 Pro and a little post processing to bring out the color and details!

    • square_peg and PhilH like this

I have imaged this nebula one time and attempted it many times. My result came out pretty good, using a Nexstar 8SE, ZEQ25 mount, ASI294MC camera, Sharpcap 3.2 Pro and a little post processing to bring out the color and details!

Care to share?

    • square_peg likes this
Photo
Stargazer3236
Dec 20 2020 08:00 AM

Here is my image of the "Robin's Egg" nebula, NGC 1360:

 

The detail seems hazy, because I over processed the image to bring out details, but the details were so over-exposed I had to soften the result.


Attached Thumbnails

  • Attached Image: NGC1360.jpg
    • PhilH and Sasa like this
Photo
Dave Mitsky
Dec 20 2020 11:49 AM

I've observed NGC 1360 a number of times, including from a location south of the equator.  It culminates at an altitude of 24 degrees at approximately 9:40 p.m. local time tonight from a latitude of 40 degrees north, as demonstrated in this screen capture (click to enlarge) from Stellarium.


Attached Thumbnails

  • Attached Image: NGC 1360 Culmination 12-20-20 Stellarium DSOs.PNG
    • PhilH and Stargazer3236 like this


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