Telescope Reviews: Binocular Icon 37 : NGC 7293, the Helix Nebula.

NGC 7293, The Helix Nebula.

Planetary nebulae are not that popular among binocular observers. Most of then remain invisible or appear like meaningless small dots in binocular instruments. Such is not the case with NGC 7293, known as the Helix or Helical Nebula. At a distance of 450 l-y, the Helix is the brightest and the largest ‘specimen’ of the planetary nebulae. Its diameter measures ¼° across. Nevertheless, the Helix is a very dim target. Its integrated brightness of magnitude 7.3 is spread over an area as large as ¼ that of the moon’s full disk. Add to that the fact that this planetary remains low to the southern horizon for mid-northern observers, and you’ll understand that the Helix can be a challenging object. I had seen it only once with a 100mm refractor, equipped with a UHC filter. So I was curious to see if I could find NGC 7293 with a pair of binoculars. The Helix can be found near the centre of the triangle formed by Delta Capricorni, Delta Aquarii and Formalhaut. I tried my luck during a clear moonless night in the French Alps. I first started my search with a pair of 8x56. I soon noticed a faint puff of smoke in the field of view. Object found! The nebula was clearly visible with averted vision as a round smudge. I suspected two faint stars bordering the west side of the nebula. The 8x56 did not reveal any particular detail in the nebula. When I finished my sketch, I mounted my 15x70 TS Marine binoculars. These binoculars provided a darker background and a better contrast. I could clearly discern more faint stars around the Helix. The nebula appeared to be brighter around its edge than near its centre. The northern rim appeared to be the brightest feature of the planetary disk, and its brightness added to the impression that the disk showed a darker centre. I was pleasantly surprised to see such details without the aid of any filter.
The sketches are presented at the end of the post. The first sketch is my impression with the 8x56 Bresser. The sketch made with the 15x70 TS Marine can be seen in the second post.

The observation with a 100mm refractor can be seen here.

Site : Le Castellard Melan, France ( 44° N )
Date : September 28, 2008
Time : around 21.00UT
First Binoculars : Bresser 8x56
FOV: 5.9°
Second Binoculars : TS Marine 15x70
FOV: 4.4°
Filter : none
Mount : Trico Machine Sky Window
Seeing : 2/5
Transp. : 4/5
Sky brightness : 21.33 magnitudes per square arc second near zenith (SQM reading).
Nelm : 6.5
Sketch Orientation : N up, W right.
Digital sketch made with Corel Paint Shop Pro X2, based on a raw pencil sketch.

(Note: if the sketch does look too dark on your monitor, try to darken the room.)

First sketch : Bresser 8x56.

Edited by rodelaet (10/05/08 12:42 PM)