Telescope Reviews: NGC 1502 and Struve 485

Dangling off the southern end of Kemble's Cascade, one the sky's better-known asterisms, you will find the open cluster catalogued as NGC 1502. Easily visible, even at low magnifications, as an unmistakable glittering mass of stars, the cluster is dominated by a brilliant pair of 7th-magnitude snow-white suns separated by 18" of arc in position angle 305°. These two are the principal members of the multiple star Struve 485 (ADS 2984; CCDM 04078+6220).

Increasing the magnification brings better definition and resolution to NGC 1502. A 7.5mm G.S-5 Plössl yielding 120x provided the most pleasing view in my scope, and this was used in the sketch presented here. All of the cluster stars appear to be pure white (or nearly so). The brightest stars in the cluster are concentrated into a narrow east-west band of stars spanning the cluster's 8' diameter. Most of these are members of the Struve 485 system.

The Catalogue of Components of Double and Multiple Stars (CCDM) lists 16 members for Struve 485 with magnitudes ranging from 7 to 14; these are designated (A-P) as indicated on the inset. Components C, E, F, G and M are very challenging due to faintness (mags 11.9-14.1) and proximity to A and B; the remaining members are quite easy by comparison. Component B is also a variable star, designated SZ Camelopardalis. It is a Beta Lyrae-type eclipsing variable with a period of just under 2.7 days and a magnitude range from 7.00 to 7.29. While component A might seem like a convenient comparison star for making magnitude estimates of SZ, it is suspected of being variable as well, with an observed amplitude of about 0.1 magnitude. Components H, I and J are also catalogued separately as Struve 484 (ADS 2982); components K and L are catalogued separately as Holmes 3 (ADS 2989).

William Herschel discovered NGC 1502 on November 3, 1787 with his 18.7-inch reflector. It is sometimes called the Golden Harp Cluster; it contains 63 member stars and lies 2,650 light years away in the direction of Camelopardalis. Its age is estimated at 5 million years.

NGC 1502 is featured in the TAAS 200 Observing List (T36), Stephen James O'Meara's recently released Hidden Treasures (HT23) and the ever-popular Herschel 400 List (H.VII.47). Struve 485 is considered one of the 200 Most Beautiful Double Stars.

Object Data:
Object Name: NGC 1502 (H.VII.47)
Object Type: Open Cluster
Constellation: Camelopardalis
Right Ascension (2000.0): 04h 07.7m
Declination (2000.0): +62° 20'
Magnitude: 5.7
Diameter: 8'
Trumpler Type: II 3 p
NGC Description: Cl, pRi, cC, iF

Object Data:
Object Name: Struve 485 (ADS 2984)
Object Type: Double Star
Constellation: Camelopardalis
Right Ascension (2000.0): 04h 07.9m
Declination (2000.0): +62° 20'
Magnitude: 7.0, 7.1
Separation: 17.9"
Position Angle: 305°

Observation Log:
Telescope: Parks Astrolight EQ6 • 6" f/6 Newtonian reflector
Eyepiece: Parks G.S-5 7.5mm Plössl
Magnification: 120x
Field of View: 26'
Filter: None
Observing Site: Oakzanita Springs, San Diego Co., CA
Date: 31 December 2007
Time: 03:30-04:30 UT
Transparency: TLM 14.4
Seeing: Pickering 7/10

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Eric
6" f/6 Parks Newtonian
10x50 Bushnell Binocs

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