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Cosmic Challenge: Emission Nebula Simeis 57

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Cosmic Challenge: September 2019

Emission Nebula Simeis 57


Phil Harrington

This month's suggested aperture range:

15-inch (38 cm) and larger telescopes









Simeis 57

Emission nebula

20h 16.2m

43° 41.2'




Simeis 57 is one of the most intriguing emission nebulae in the late summer sky, yet it is almost unknown to visual observers.  Photographers, however, know it as a pair of opposing arcs of reddish light, one extending to the north, the other to the south, that appear to be spinning symmetrically away from a common center.  Its unusual appearance has led to its two nicknames: the Propeller Nebula or the Garden Sprinkler Nebula. 

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

Above: Finder chart for this month's Cosmic Challenge.
Click on the chart to open a printable PDF version.

The entire complex was assigned Simeis 57 when it was discovered in the early 1950s by G.A Shajn and V.E. Hase at the Crimean Astrophysical Observatory at Simeis, Russia.  Their results were published in the observatory's Bulletin of the Crimean Astrophysical Observatory (in Russian, Izvestiya Krymskoi Astrofizicheskoi Observatorii), although they did not become widely known outside of the Soviet Union at the time, probably due to the Cold War raging at the time.

Later, portions of Simeis 57 were assigned separate designations in various catalogs.  The propeller's southern blade is listed as DWB 111, after a 1969 article detailing the Cygnus X region, written by H. R. Dickel, H. Wendker, and J.H. Bieritz that appeared in the journal Astronomy & Astrophysics (A&A, vol. 1, p. 270 - 280).  The same article listed the northern blade as DWB 119.  Fainter sections were assigned other DWB numbers, although for our purposes here, we will concentrate on trying to see the propeller itself.  That's tough enough.  (Sidebar: For a more up-to-date review of the physics behind Simeis 57, read The peculiar nebula Simeis 57-I. Ionized gas and dust extinction, also published in Astronomy and Astrophysics [A&A vol. 398, p. 1063-1071].)

As with so many emission nebulae (or hydrogen-II regions, if you prefer), the Propeller Nebula is very difficult to see by eye alone.  That's because its primary emissions lie in the red portion of the visible spectrum, where our eyes are all but blind under dim light conditions.  And they don't come much dimmer than Simeis 57.

The blades of the propeller span about 20', so in order to squeeze both into the same view, select an eyepiece with a real-field coverage of at least half a degree.  A modern, ultra-wide design with an 80°-plus apparent field is better than, say, a more conventional Plössl, since their wide apparent fields also produce a higher magnification for the given real field.  That's important consideration, since higher magnification will generate better image contrast.

To boost contrast further, experiment with various nebula filters.  Not to plant any preconceived prejudices in your mind, but narrowband (UHC-type) and O-III filters seem to offer little positive effect on the Propeller.  On the other hand, a Hydrogen-Beta (Hβ) filter, which rarely seems to help objects beyond the Horsehead Nebula, usually proves to be the top choice here.  But again, try each filter in your cadre and see which produces the best results.

The Propeller is 5° southwest of Deneb [Alpha (α) Cygni], and just to the west of a right triangle the 7th-magnitude stars SAO 49403, 49413, and 49418.  While that triangle is obvious in the 8x50 finderscope attached to my 18-inch, the Propeller itself takes better skies than I can hope for from my suburban observatory.  Under naked-eye limiting magnitude 6.5 skies, however, the 18-inch at 94x and with an Hβ filter in place reveals a very soft glow after a concentrated search.

Above:  Simeis 57 as seen through the author's 18-inch (46cm) reflector

Of the two blades, the northern component, DWB 119, impresses me as slightly more obvious.  It lies just northwest of the triangle.  My notes recall the softest of glows, a gentle, concave arc opening toward the west.  Two close-set 12th-magnitude stars appear centered along the length of the arc, while an 11th-magnitude star marks its northern tip.

The southern blade (DWB 111) is a tougher catch.  Look for a close pair of 9th-magnitude stars just to its west; they make a handy reference marker in much the same way as 52 Cygni does for the NGC 6960 segment of the Veil Nebula.  DWB 111 is a mirror image of DWB 119, with its curve opening to the east, more or less toward the right triangle of stars.

Interested in hunting for more Simeis objects? CN'er ngc4565adam started a thread in the Deep Sky forum some years back asking for a source of the catalog.  A pair of Steves (Saber and Gottlieb) posted replies. The former Steve (Saber) shared a link to SIMBAD that gives 231 entries, while the latter (Gottlieb) offered a second link listing some pertinent Simeis publications. The thread and links are all worth visiting.

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.  A revised, second printing of Cosmic Challenge: The Ultimate Observing List for Amateurs is now available with updated data tables and charts for finding various solar system objects, such as Pluto and Vesta, as well as improved renditions of the many eyepiece sketches that accompany each of the 187 challenges encompassing more than 500 individual objects.  The book is available from Amazon.com.  Visit www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2019 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.


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