M 7 (NGC 6475) Open Cluster in Scorpius

Located at: RA 17 hours 53 minutes 54 seconds, Dec -34 degrees 47 minutes 00 seconds

Size: 80' (50'-75')* Magnitude: 3.3 Class: I 3 r

North is up

West to the right

Telescope:

 8" f5 Newtonian reflector

Camera:

Miranda Laborec 35mm camera, manually guided, hypered Kodak Technical Pan 2415 film, 37 F outside temp

Image:

No filter, 40 minutes, 08/26/1990

Processing:

D-19, 6.0 minutes @ 69F, 35mm negative scanned with Polaroid SprintScan 4000 (4000 dpi)

Scan is a crop from 35mm negative, scan processed in Photoshop CS5.1

Location:

Mt Pinos, CA

Notes:* This cropped field with the 8" is approximately 1.3 x 2.5 degrees, and contains several other objects. In addition to M 7 (centered), my software lists a Globular Cluster (NGC 6453), parts of a several other Open Clusters (NGC 6444, NGC 6455 and Cr 355), and a couple of small Planetary Nebulae. My software (Megastar v5.0.13) does not identify the Dark Nebula within the borders of M 7, but the online Barnard Atlas (Plate 24) indicates it is B 287.

This is a recent (06/26/2012) scan, as I had hooked up my scanner to capture the last few Messier film negatives for this project.

Most of the film scans from the 8" f5 Newtonian reflector were centered on the object of interest, and were generally scanned to file as a 2000 x 2000 pixel crop of the 35mm negative. This image is a scan of about 80% of the 35mm negative (3500 x 5400 pixels).

Reduced in Photoshop to 1600 pixels, and saved under "Save for Web & Devices".

From the NGC / IC Project:

*According to "Star Clusters", by Brent Archinal and Steven Hynes; "50' diameter, 75' diameter with outliers".

Contemporary Visual Observation(s) for NGC 6475
NGC 6475 = M7 = E394-SC9 = Cr 354
17 53 51 -34 47.6
V = 3.3;  Size 80

18" (7/21/04): at 92x at least 300 stars are visible in the cluster, though very 
difficult to count due to the very large size (overfills the 42' field).  The 
more concentrated part of the cluster spans perhaps 30' and includes a dozen 
stars of mag 7.5 or brighter in the main body.  This cluster is much larger and 
brighter (very prominent naked-eye), but it is much more scattered than M6 and 
so is less impressive.  There are several bright, distinctive strings in the 
cluster including a N-S string of ~8 stars on the east side of the central 
region.  An equilateral triangle of mag 6, 7 and 8 stars with sides of 3' is on 
the NW side of the core of the cluster.  A clump of 5 stars is near the center 
including two mag 6 and 7 stars.  On the south side of the center of the cluster 
is an 11' string of 5 mag 5.6 to 7.8 stars oriented SW-NE with the bright mag 
5.6 star on the SW end a distinctive yellow color.

13.1": very bright, very large, impressive but scattered, overfills 52' field.  
Open cluster H18 lies 45' SE and globular cluster N6453 40' WNW of center.  
Prominent naked-eye cluster in dark sky.  Includes several blue-white and 
yellowish stars.

8": overfills 40' field, not many faint stars, scattered.

- by Steve Gottlieb

This description of B 287 from the on-line Edward Emerson Barnard "A Photographic Atlas of Selected Regions of The Milky Way":

287
α(2000)17h 54m 27s, δ(2000) -35 13
Galactic Coordinates 356, -5
 Irregular, semi-vacancy, diam. 1/2, SE of M 7