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Latest Website Update [1 March 2015] >> A new Object of the Season for Spring 2015 >> March Double Star of the Month

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March 2015 - Double Star of the Month

With Cancer now moving inexorably towards the western horizon, its stars are becoming more comfortably accessible to the classical refractor user and one of its finest doubles is 57 Cnc (08 54 14.70 +30 34 45.0).

According to Webb, it is a pair of crocus-yellow stars which are not quite equal in brightness (magnitudes 6.1 and 6.4). There has been little motion of any kind save a small increase in both position angle and separation with the result that the separation is now well over 1".

It is an ideal test for a 7.5-cm refractor. Webb was able to divide it at x144 on his 3.7-inch Tulley OG, and the writer found 1".55 with the Cambridge 8-inch in 2006.

The pair is almost certainly binary in nature as the proper motion of the system would have separated them a long time ago. A faint component can be found at 55" and PA 202° which appears fixed. The WDS gives its magnitude as 9.2.

57 Cnc is about 2.5 degrees north following the spectacular wide pair iota Cnc.

Gamma Sextantis, also called 8 Sextantis (09 53 30.47 -08 06 17.7) was discovered on 1852 Apr 7 by Alvan Clark with a 12-cm aperture. As it happens he observed the star at a suitable part of its orbit but this discovery is a good indication of the quality of Clark's telescopes.

He said, reporting his finds in Monthly Notices for 1857, Notwthstanding the moderate meridional altitude of of 8 Sextantis at Dorpat (about 24°), it may reasonably be doubted whether its duplicity would have been left to be discovered with a 4 3/4-inch object-glass, however perfect, if no change had occurred in its appearance since Struve's scrutiny of that part of the heavens.

The separation of this close pair is never wider than 0".6. It reached maximum separation in its 77.8 year cycle in 2002 and is now closing again. By Spring 2015 it will be at 44°, 0".54 and the low declination means that it will be a significant test for 20-cm and its more likely that a good, steady air will be essential to resolve it, especially as there is a considerable difference in brightness between the components - A is 5.4 and B is 6.4. Hipparcos places the system at 278 light years distance and the primary is an A1 dwarf.

To find gamma Sextantis, locate alpha Hya and move 5 degrees east.

Bob Argyle - Double Star Section Director

January 2015 - Picture of the Month

Sh2-155 The Cave Nebula in Cepheus

Our images this month are courtesy of David Davies from Cambridge in the UK. They provide an interesting comparison of the difference aperture can make when imaging nebulae. Please click on either image for the high resolution version. For more images from David please visit his Flickr Photostream.

I've been collecting data for an image of the Cave Nebula over four nights during December (5, 7, 13 15) and it has been a chapter of carelessness and frustration. I ended up binning hours of data after discovering it was slightly out of focus or was captured with the wrong filters. In the end I did some work on what I could rescue and the attached image is the result.

I set off trying to image the Cave in narrow-band but soon discovered that although the main cup-shaped nebula is rated as reasonably bright (integrated magnitude 7) it covers around 15 arc minutes of sky and is quite faint. The surrounding nebulosity comprising emission, reflection and dark nebulae is much fainter. Hydrogen-alpha emission can be acquired fairly readily but oxygen III and sulphur II emissions are very faint indeed. I decided to cut my losses and abandoned my acquisition of oxygen and sulphur, changed the filter wheel to RGB and acquired around an hour of each.

I was interested to see the Cave in its context and chose to image it with my ED120 refractor plus a reducer/flattener to give a field of view of 81 x 61 arc minutes. The attached image is a crop to approximately 60 x 60 arc minutes.

The Cave Nebula (Sh2-155) with an Equinox ED120 - Image Courtesy of David Davies

The image is Hydrogen-alpha, RGB; four hours of hydrogen-alpha in 20 minute subs; 132 minutes of RGB in 8-minute subs; all binned 1 x 1. Processing was in Pixinsight with a final touch-up in Photoshop.

  • Telescope is Skywatcher Equinox ED120 with a Skywatcher X0.85 reducer/flattener.
  • Camera is a QSI 583 wsg with Astrodon LRGB and 3 nm narrow band filters and Lodestar guide camera.
  • Mount is a Skywatcher NEQ6 controlled via EQMOD.
  • Image capture was with Nebulosity and Scopefocus for automatic focusing.

I was curious to see what my 10-inch Newtonian would make of it so here is the Cave again but this time captured with a 10-inch Newtonian. The faster optics and longer exposures have yielded a deeper image.

The Cave Nebula (Sh2-155) with a 10 inch newtonian - Image Courtesy of David Davies

A hydrogen-alpha RGB image captured on the nights of 19 and 24 December 2014 from Cambridge, UK. Two hours each of RGB in 10-minute subs plus one hour of hydrogen-alpha in 20-minute subs.

  • Telescope is a 10-inch Newtonian plus Televue Paracorr at F/4.5.
  • Camera is a QSI 583 wsg with a Lodestar camera as off-axis guider.
  • Mount is a Skywatcher NEQ6.
  • Image processing with PixInsight and Photoshop.

Object of the Season (Spring 2015)

NGC 6572 in Ophiuchus

Planetary Nebula NGC 6572 in Ophiuchus will be announced in DSO 167, and the results will be published in DSO 169.

NGC6572 - Image Courtesy of Hubble Space Telescope (HST) This image was supplied by the Hubble Space Telescope (HST).

Position (2000)
18 12 06.4 +06 51 15 (Oph)
Visual magnitude
8.1 mag
Central Star
13.6 mag
Size
0.6' x 0.4'
Distance
2500 ly
Other Designations
Σ 6, h 2000, GC 4390, PK 34+11-1, VV 159, ARO 7

Wolfgang Steinicke - Nebulae and Clusters Section Director

February 2015 - Galaxy of the Month

NGC 2275 Group in Gemini

NGC2275 Group - Image Courtesy the Sloan Sky Survey

This image the NGC 2275 group was provided by the Sloan Sky Survey, and this finder chart should help you locate these galaxies.

Finding galaxies in the winter constellation is always a challenge as most are quite faint and in general overlooked. With Gemini riding high on the meridian on February nights the challenge was to find a galaxy that was not really just for imagers. The NGC 2274/5 pair seemed to be a good challenge. There are not many observations of this galaxy pair and it is not included in either the NSOG or L&S. Both galaxies were discovered by William Herschel (who else ☺) in 1786.

NGC 2274 is the brighter of the two being an elliptical galaxy. At 12th magnitude this may be a challenge to find. Its companion NGC 2275 is actually much fainter and is an unclassified spiral. It appears to be undergoing some form of interaction as one of its spirals arms is much more obvious than the other. I am sure it would have made Arp’s famous catalogue if it was a brighter pair.

The pair is actually part of a small group of galaxies which has been variously catalogued as LGG 139 or WBL 121. The group consists of the four galaxies, NGC 2274, 2275, 2290 and UGC 3537. NGC 2290 is actually quite a distance from the others at 47’ of arc away. It appears with another group of galaxies which are in fact unrelated. NGC 2290 was also discovered by William Herschel but in 1793. The separation is due to the fact that the group is relatively close to us at about 4.6 Mpc so the group is spread out on the sky.

NGC 2274 and 2275 have been reported with apertures as small as 15cm from very dark sites but I suspect that probably 30cm will be needed from most normal sites, certainly to see NGC 2275. The other galaxy in the group UGC 3537 appears to be a face on spiral and is quite faint and is going to be a challenge to see unless you have a large telescope or use video or CCD imaging.

NGC2290 - Image Courtesy the Sloan Sky Survey

This image of NGC 2290 was provided by the Sloan Sky Survey.

The group of galaxies around NGC 2290 will also make a nice target but will be a challenge for large telescope owners as these galaxies are much fainter.

Owen Brazell - Galaxy Section Director

Deep-Sky Observer (DSO) No 153 - Free Sample

DSO153 Cover

This free journal is DSO 153 from 2010. You can download it as a PDF file onto your computer by right clicking the link below and choosing either 'Save Target As' or 'Save Link As'...

Download DSO 153 (2MB PDF file)

The Brightest Planetary Nebulae Observing Atlas - 2nd Edition

Massimo Zecchin has just completed the 2nd Edition of an atlas of planetary nebulae observed with small apertures and from suburban locations, entitled: "The Brightest Planetary Nebulae Observing Atlas".

Massimo has kindly made the atlas is freely available in two versions, Black (for display) and White (printer friendly with the images in negative).

The 2nd Edition contains:

  • Six additional objects.
  • Data of visual magnitude, central star magnitude and object size from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (SEC catalogue) and in a few cases from the Saguaro Astronomy Club database (SAC catalogue).
  • Calculated surficial brightness for any object (in magnitude per square arcsec).
  • Six additionaltables showing the objects sorted by magnitude, surficial brightness, size, central star mag, constellation and declination.
  • A general position map.

Either version of the atlas can be downloaded as a PDF file onto your computer by right clicking the respective image above and choosing either Save Target As or Save Link As...

Please note that the Black version is 14MB and the White version 10MB