Astro Images

 Designations: M103, NGC581
Object Type:  Open Cluster
Constellation: Cassiopeia
RA: 1h 33.4m
Dec: +60 deg 39.5m

Visual Magnitude: 7.4
Size: 6'
Distance: 8130 light years
Discoverer: Pierre Mechain, 1781

Visual Description: Stars in an open cluster are destined to be fickle. Without the "glue" of strong mutual gravitation to hold them together - as the hundreds thousands of stars are held together in a globular cluster - they gradually separate from the main pack and form other alliances. Or, like our sun, travel solo through the emptiness of space. When we look at a loose cluster of stars through a telescope, then, it is difficult to judge what state of association, or disassociation, it is in. The last object in Messier's original catalogue, M103 in Cassiopeia, is a case in point. Astronomer Harlow Shapley went so far as to call this stellar sprinkle a possible chance alignment stars. But recent data suggest that Ml03 is a true cluster with as many 172 stars in an area of only 6' of arc.

Located about 1° northeast of Delta (δ) Cassiopeia, the cluster easily spied in 7 x 35 binoculars, which also resolve the cluster's brighter stars, the brightest being magnitude 10.5. The view through the telescope is really best at low power, when the loose grouping appears more compact. When the brilliant Delta is placed on the western side of the low-power field of view, M103 lies between it and a congregation of four other open clusters to the east! What a dynamic field, even if these clusters are not related.

M103 is clearly the brightest of the five clusters, and it is easily distinguished by its Christmas-tree shape. The luminous star at the apex of the tree is Struve 131, a double star with 7.3- and 10.5-magnitude components separated by nearly 14"; Smyth saw their colors as straw and dusky blue. Apparently this double is not a true member of the cluster, though

Smyth also saw a red 8th-magnitude star southwest of the brightest star in the cluster. D'Arrest described this same star shining with a rose tint but he recorded it as 10^th magnitude.  Luginbuhl and Skiff describe it as “very red” and shining at magnitude 8.5.  Photometric measurements confirm that the star is fairly red.  And as for me, curiously, I so no reddish color at all.

Telescope: TMB 152mm APO Refractor
Focal Length: 1201mm * 0.8x focual reducer (961mm)
Mount: Takahashi NJP 160
Camera: Starlight XPress MX916
Exposure: Multiple 20 second exposures
Other: SBIG STV guider

Astro Images

doug@dougsastro.net

Copyright(c) 2007 Doug Sanqunetti. All rights reserved