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Constellation: Gemini
Proper
Name







Castor
Pollux
Alhena
Wasat
Mebsuta
Propus
Apparent
Magnitude
m
1.59
1.16
1.93
3.51
2.98
4.4 to 5.2
3.33
Which star is hottest?
Absolute
Magnitude
M
0.90
0.95
-0.71
2.5
-4.6
-4.6 (average)
-0.71
Distance
lyrs
Spectral Type
Luminosity Class
45
35
105
53
1100
1500
200
A1 V
K0 III
A0 IV
F0 IV
G8 Ib
F7 Ib to G3 Ib
M3 III
Single or
Multiple
Star System
Binary
Single
Single
Binary
Single
Cepheid Variable
Binary
Coolest?
Which star appears brightest?
Which star is the most luminous?
Dimmest?
Least luminous?
Which stars are main sequence stars?
Which stars are the largest in radius?
Why does Mebsuta appear so dim given that it is very luminous?
Explain the difference in luminosity between Castor and Alhena.
If the distance to Castor and Pollux were not shown, how could you determine which was farther away?
M 35
Open Cluster M35 (NGC 2168), type 'e', in Gemini
Right Ascension
Declination
06 : 08.9 (h:m)
+24 : 20 (deg:m)
Distance
2.8 (kly)
Visual Brightness
5.3 (mag)
Apparent Dimension
28.0 (arc min)
http://www.seds.org/messier/Jpg/m35.jpg
Discovered by Philippe Loys de Chéseaux 1745-46. Independently discovered by John Bevis
before 1750.
Open star cluster M35 is consisted of several hundred stars (of which Wallenquist has counted
120 brighter than mag 13) scattered over the area covered by the full Moon (30'); the Sky
Catalogue 2000.0 and the first edition of Uranometria 2000.0 give 200 members, the second
edition of Uranometria 2000.0 gives 434, while Cudworth (1971) counted 513 probable member
stars. At its distance of 2,700 (WEBDA) or 2,800 light years (Sky Catalogue 2000.0), this
corresponds to a linear diameter of about 24 light years; its central density is about 6.21 stars per
cubic parsec. Some authors have estimated a larger diameter of up to 46' (H. Shapley in 1930).
With about 100 million years (WEBDA gives a value 95, the Sky Catalogue 2000.0 of 110
million years), it is of intermediate age, and contains some post-main sequence stars (including
several yellow and orange giants of spectral type late G to early K). Its hottest main sequence
star is given as of spectral class B3 (Sky Catalogue 2000.0), and its Trumpler classification as
III,3,r by all sources. It is approaching us at 5 km/sec.
Even the naked eye finds this cluster easily near the 3 "foot stars" of Gemini under fairly good
observing conditions. The slightest optical instrument will resolve the brighter stars and make it
a splendid view at low magnifications, a nearly circular cluster with rather uniform stellar
distribution. In telescopes, low powers and wide-field eye pieces show M35 at its best.
Amateurs with more powerful telescopes can view its fainter neighbor, NGC 2158 (at the upper
left in our image); it is situated just about 15 arc minutes southwest of M35. NGC 2158, of about
mag 8.6 and about 5 arc minutes angular diameter, contains many more stars, is much more
compact, over 10 times older and over five times more remote than M35 (the Sky Catalogue
200.0 gives about 16,000 light years), and because it consists of older stars, its light is dominated
by yellower stars; the hottest star is of spectral type F0. Because of these properties, NGC 2158
was once even taken for a globular cluster candidate.