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2nd Feb Orion


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Early this evening the sky looked crystal clear so I set the scope up on the patio in the back garden to cool down at about 6.45pm, not that it needed much cooling as I keep it in the garage which is probably only slightly above the external temperature. Had to deal with the Tesco grocery delivery and a few other chores and went out to observe about 8pm. After a bit of dark adaptation I was disappointed to realise that the sky had deteriorated considerably and the earlier transparancy had gone. Anyway, I still got an interesting couple of hours in, star hopping to various objects from memory, since I had forgot to bring out a star map and didn't want to lose any dark adaptation going in to get it. On a previous cloudy night, I had been swotting up on clusters in Orion and was amazed how busy Collinder had been in and around this constellation. Swedish astronomer Per Collinder's 1931 catalog contains 471 star clusters, the most well known probably being Cr 399 the Coathanger asterism or Brocchi's Cluster in Vulpecula. He lists twelve clusters in Orion.

First off, it had to be the Orion nebula and it did not disappoint. I tried it with various eps but the best view in the 10" SNT was with the 14mm 100 degree and 2x barlow at 145x. It was brighter than I had ever seen it and showed greater detail than in any other scope I had looked through. The OIII filter made it stand out more by darkening the background but dramatically reducing the star brightness. A slightly more pleasing view was gained using a UHC filter with the stars and trapezium being brighter. At 145x it spanned edge to edge of the 0.7 degree field and the full extent of the wings required a bit of panning left and right. The fish's mouth was very prominent and M43 showed some detail. The 23mm 82 degree ep at 44x with a 1.9 degree field nicely framed most of this superb complex including south to north NGC 1980 = Collinder 72, M42, M43 and NGC 1977 and panning just half the field north showed the bright cluster NGC 1981 = Collinder 73. In NGC 1977 at higher power I suspected a hint of nebulosity with averted vision, but certainly no Running Man. Tried to find the small nebula NGC 1999 slightly south and east of M42 without success, bet I'd have bagged it using the map.

On a line between M42 and Saiph is the cluster Streicher 58, this showed as a nice looking string of nine 11th mag stars in almost a straight line with a brighter 9th mag star at each end. This unusual line of stars is nearly half a degree long.

Orions Belt Cluster is Collinder 70 and made lovely sight in the 12x80 finder which framed it perfectly in the 4.5 degree field. This contains an incredible richness of stars with a large variations of brightness. This is a georgeous region to see in binoculars or a rich field scope and reminds me very much of the Alpha Perseus cluster in size and richness. The most striking feature is a long S shaped string of stars snaking through the belt.

Sigma Orionis and its close neighbour Struve 761 make a fine sight at higher powers, looking like a small close knit star cluster. Actually two multiple star systems.

M78 was easy to find looking very slightly fuzzy in the finder. In the 10" it was surprisingly unimpressive, looking like a double star through a dewing corrector plate. On checking with a red torch the corrector was fine and I had already checked that dew was unlikely on this occasion.

Elosser 1 is a cluster (asterism according to some sources) in Orions bearskin shield and is a prominent small group of stars from mag 7 to 12 nicely framed in the 14mm. Nearby and a little north is NGC 1662 = Collinder 55, another pretty compact cluster of about 20 stars in the 10". These two clusters easily showed in a single field of view through the finder.

Dolidze 17 is a small compact cluster of about eight mostly 8th mag stars just NW of Bellatrix. Nothing too exciting but it is easily found. Some sources list it as a suspected asterism rather than a proper cluster.

Collinder 69 is the cluster at the head of Orion, including Lambda Ori. It is a large, bright grouping which looks very pretty in a wide field. It completely fills the field of the 23mm 82 degree Axiom possibly looks better in the finder.

NGC 2169 = Collinder 83 is one of my favourites in north east part of Orion. Some see it as a number 37 (backwards or inverted depending on the scope) but I just like it as a compact prominent cluster that looks great at higher powers. This cluster is the most distant of those observed tonight at about 3000 light years. Most of the other clusters seen are at 1200 to 1400 light years which is a similar distance as the Orion Nebula. Using a wide field ep and panning east for a degree from 2169 brings into view the bright asterism Persson 1. A nice curvy line of about a dozen 7th mag stars nearly one and a half degrees long. This pair of objects looks great in the wide field of the 12x80 finder.

I moved slightly up and out of Orion to Taurus to find something I had never seen before. Lorenzin 1 an asterism. Extend the constellation line from Aldebaran through zeta tauri (the horn near M1) and half a degree past zeta you will easily find a near straight line of stars continuing the line for nearly one and a half degrees. All the stars are 8th to 10th mag and end in a small ringlike cluster of stars which includes a nice 8th mag double star with fainter components.

Looking at the main stars in Ursa Minor, I reckon the limiting magnitude was only around mag 4.5 after dark adaptation. I have seen at least a magnitude fainter from my backyard and even more a few years back when we had a power outtage over a large area and the sky was probably better than the best I have seen at Belper. The above viewing session was very enjoyable, but an extra magnitude (which I reckon was the situation earlier in the evening) would have really made a big difference to the richness of all these objects through the scope. My new book (Star Clusters by Brent Archinal and Steven Hynes) details 53 star clusters in Orion and I found about 8 others from different sources, of which at least half should be visible in a 10"! 


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