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Cosmic Challenge: IC 1613

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Cosmic Challenge:
IC 1613


November 2022

Phil Harrington

This month's suggested aperture range:

10- to 14-inch (25-36 cm) telescopes











IC 1613


01m 04.8m

+02° 17.1'





The Local Group of galaxies includes three large spiral galaxies the Milky Way, the Andromeda Galaxy, and the Triangulum Spiral and dozens of smaller systems.  Two of the toughest to see are found in the constellation Cetus and make up this two-month challenge.


We begin with IC 1613, discovered in 1906 by German astronomer Max Wolf on photographs taken with the Bruce 16-inch (41-cm) refractor at the Astrophysical Observatory in Heidelberg.  Using data from the Hubble Space Telescope in 1999, Andrew Cole and colleagues confirmed that IC 1613 lies 2.4 million light years away.  This places it a bit closer to us than M31 and its cadre of satellites.  Like that galactic family, IC 1613 is also approaching the Milky Way, in this case at a rate of 234 km per second. While that is comparable to NGC 147, one of M31's companions, IC 1613 is not gravitational kin to Andromeda.  In fact, it is nearly as far away from M31 as it is from the Milky Way.

Above: Late 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



Despite being relatively nearby, IC 1613 suffers from the same problem that plagues many other Local Group members, such as previous challenges Leo I, Leo II, and Leo III (aka Leo A).  Like those systems, the feeble light from IC 1613 is spread across such a large area that its surface brightness drops precipitously.  Although it is listed as 9th magnitude, remember that is its integrated brightness, or how bright it would appear were it compressed to a stellar point.  The fact that the galaxy is spread across an area half the apparent diameter of the Full Moon lowers its surface brightness to only magnitude 15.5.


Although it can be a bear to see, IC 1613 is not hard to locate thanks to its proximity to 26 Ceti.  To get there, aim your finderscope along the rope attached to the southern Fish's tail at Epsilon (ε) Piscium.  Look 2½° south-southeast of Epsilon for an equilateral triangle of stars made up of 73, 77, and 80 Piscium.  From here, move about 4° south to 26 Ceti.  Be careful not to confuse it with 29 Ceti, which is more to the east-northeast.  IC 1613 is 47' north of 26 Ceti and just 11' south of an orangish 7th-magnitude sun, SAO 109653.


The galaxy's large apparent size conspires with its low surface brightness to make this such a difficult catch.  In order to squeeze it all into a single eyepiece field, we need to use low power.  But low power also lowers image contrast.  Higher magnifications boost contrast, but reduce the field size too much.  It's a vicious circle that requires experimentation to solve.  In my 18 inch (46 cm), I have found the best compromise to be a 22-mm Tele Vue Panoptic eyepiece that yields 94x and a real field measuring 42' in diameter.


With that combination, I can make out that the northeastern section is slightly brighter than the region toward the southwest, but beyond that, I see no distinct boundaries.  Instead, the galaxy just diffuses softly into the background.



Above: Sketch of IC 1613 as seen through the author's 18-inch (46-cm) Newtonian reflector at 94x.



Photographs, such as the great image below by CN'er George Simon, show that IC 1613's internal structure is both loosely and poorly organized.  Outwardly, it resembles Barnard's Galaxy, NGC 6822, although its total mass is far less.  IC 1613 has an estimated mass equal to just 80 million Suns.  By comparison, NGC 6822 has a mass equal to 130 million Suns.  Like that summertime object, IC 1613 is designated as a dwarf barred irregular, a strangely bloated mishmash highlighted by an axial "bar" across its core.  There is also the subtle suggestion of spirality, with a gently curving extension tapering away from a jumbled core.


A brighter northeastern segment corresponds to a region populated with blue-giant stars distributed among more than two dozen stellar associations.  The galaxy also contains more than two dozen very small star clusters, as well as a dozen small nebulae.  Under extraordinary conditions the largest scopes may be able to just resolve some of these distant deep-sky objects, as well as several background galaxies shining through IC 1613 itself.



Above: A wonderful image of IC 1613 taken with a TPO/GSO 6" f/6 Imaging Newtonian and Nikon D5300 camera.

Credit: George Simon. Visit his Astrobin page for more information about this and his other great images.



Don't get too full of yourself if you see IC 1613 through your "big" telescope, however.  Arizona astronomer Brian Skiff has seen it through his 2.8-inch (7.1-cm) refractor, while super-eyed Steve O'Meara reports an observation of IC 1613 through his 4-inch (10.2-cm) refractor from a high-altitude site in Hawaii.


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 website or post to this month's discussion forum.


Until next month, when we take an even deeper dive into the Local Group, 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 2022 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.


  • John O'Hara and rojavastars like this


Yes, I love these objects. And always feel the same thing when I sweep over them --- "Oh... that's it! bigger and more subtle than I anticipated". I think the ~feathered~ nature of the distribution also adds to challenge.    Tom

    • PhilH and John O'Hara like this

Good target, and this time of year (November) is a favorable time to observe it since the gegenschein has moved past it now.  With the galaxy's very low overall surface brightness and location near the ecliptic, the presence of the gegenschein surrounding it brightens the foreground sky considerably making it harder to detect.


Skiff and O'Meara's sightings through small and mid-size refractors are unsurprising to me.  I was able to see it with my ST80 at 16x being used as a finder on the 20" several years ago in ~21.5 mpsas conditions.  With the 20" I could identify key portions of the structure, and with a UHC filter I could detect some of the emission nebulae within.  


Knowing where to look, particularly after having seen it in larger aperture, makes some low/very low surface brightness targets recognizable in small apertures.  The globular NGC 5053 is similar in surface brightness and total magnitude, and in dark skies I have seen it in the 20", then identified it clearly in the ST80 at 16x, then found it in a 10", and finally in the latter scope's 50mm finder at the threshold--definite, but the faintest haze if one knew where to look and studied the field for a time.   


One negative this year (and last) has been increasing solar activity, which increases the average night time natural air glow.  My sites have been running on the bright side over much of the past two years.  That doesn't matter much for higher surface brightness targets, but for diffuse threshold levels of contrast it makes an outsized difference.

    • PhilH and John O'Hara like this
David Knisely
Nov 01 2022 09:55 AM

The first time I tracked down IC 1613, it was in my 10 inch f/5.6 Newtonian way back in October of 2001, and it was fairly difficult, as its mean surface brightness is around 15th magnitude per square arc minute.  I could see a very faint somewhat diffuse glow elongated northwest to southeast, with a hint of another patch just off its northeastern edge.  However, at the time, I had my little 80mm f/5 "short tube" refractor set up nearby, and surprisingly, at only 16x, it too showed the object, although again, it was pretty faint.

    • PhilH and John O'Hara like this
Alex Swartzinski
Nov 25 2022 05:30 PM

On Wednesday night, I had some of the best conditions since June at the dark site. It was super transparent and clear, so I took a shot at IC 1613.


It was easy to miss at first because of the diffuse nature of this object, but once I knew where to look the 15" made quick work of it.


I left my notebook at the dark site, but my notes pretty much describe this object as a circular halo that's brightest at the center and tappers gradually in all directions. Averted vision made this object extend a little farther, but it was mostly round and very similar to a large diffuse planetary nebula.


The only thing I missed on this object was the HII regions. Steve Gottlieb's NGC notes show that the largest region is accessible to an 18", and I'm sure it was possible with the conditions I had. I just forgot to look for it! 


This was a nice galaxy to add onto my local group collection! 

    • PhilH likes this

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