Mercury to rescue the two daughters of the King of
Thebes, who were about to be assassinated by their wicked
stepmother. Aries is fairly distinctive, with a small trio
of stars (·, ‚, Á) of which ·, or Hamal, is reddish and of
the second magnitude. Á, or Mesartim, is a wide, easy
double with equal components. Binoculars will not split it,
but almost any small telescope will do so.
Perseus. The gallant hero is well represented in the sky,
and has an easily identified shape. The constellation is
immersed in the Milky Way, and is very rich. There are no
first-magnitude stars, but the leader, ·or Mirphak, is not
far below. It is of type F, 620 light-years away and 6000
times as luminous as the Sun.
‚, or Algol, is the prototype eclipsing binary, and one
of the most famous stars in the sky; it lies in the head of
Medusa, the Gorgon, who had been decapitated by Perseus
but whose glance could still turn any living creature to
stone. Algol’s period is 2 days 20 hours 48 minutes 56 sec-
onds; the primary eclipse is only about 72 per cent total,
but is enough to drop the apparent magnitude from 2.1 to
3.4. The secondary minimum, when the fainter component
is hidden, amounts to less than a tenth of a magnitude.
The main component (A) is of type B, and is a white
star 100 times as luminous as the Sun, with a diameter of
4 million kilometres (2.5 million miles). The secondary
(B) is of type G; it is about three times as luminous as
the Sun, and is about 5.5 million kilometres (3.4 million
miles) across, so that it is larger though less massive than
the primary. The true separation is around 10.5 million
kilometres (6.5 million miles), so that the components are
too close together to be seen separately; there is also a
third star in the system, well away from the eclipsing pair.
We can work out a good deal about the evolution of
the Algol system. Originally the secondary (B) was more
massive than its partner, so that it swelled out and left the
Main Sequence earlier. As it expanded, its gravitational
grip on its outer layers weakened, and material was cap-
tured by the other star (A), which eventually became the
more massive of the two. The process is still going on.
The system is a source of radio waves, from which we
can tell that a stream of material is making its way from
B to A. This is what is termed mass transfer, and is of the
utmost importance in all studies of binary systems.
The fluctuations of Algol are easy to follow with the
naked eye; the times of mimima are given in almanacs
or in monthly astronomy periodicals such as Sky &
Telescope. Suitable comparison stars are ̇(2.85), Â(2.89)
and Î(3.80), as well as ÁAndromedae (2.14). Mirphak is
rather too bright. Avoid using ÚPersei, which is a red
semi-regular variable with a range of magnitude from 3 to
4, and a very rough period which may range between 33
and 55 days.
̇Persei is highly luminous (15,000 times as powerful
as the Sun) and is the senior member of a ‘stellar associa-
tion’, made up of a group of hot, luminous stars which are
moving outwards from a common centre and presumably
had a common origin. In the same binocular field with
̇ are Ô(3.83) and the irregular variable X Persei, which
has a range of between magnitudes 6 and 7 and is of
special note because it is an X-ray emitter.
M34, an open cluster near Algol, can be seen with
binoculars. However, it pales in comparison with NGC
869 and 885, which make up the Sword-Handle. They are
easy to locate – Áand ‰, in the W of Cassiopeia, point to
them – and can be seen with the naked eye; telescopes
show a wonderful pair of clusters in the same low-power
field. They rank among the most beautiful sights in the
stellar sky.STAR MAP 12
BRIGHTEST STARS
No. Star R.A. Dec. Mag. Spectrum Proper name
hm s ° ‘ “
21 · 00 08 23 29 05 26 2.06 A0p Alpheratz
43 ‚ 01 09 44 35 37 14 2.06 M0 Mirach
57 Á 02 03 54 42 19 47 2.14 K2A0 Almaak
31 ‰ 00 39 20 30 51 40 3.27
Also above magnitude 4.3: 51 (3.57), Û(3.6v), Ï(3.82), Ì(3.87), Í(4.06), ̆(4.09) Î(4.14), Ê(4.25), È(4.29)
VARIABLES
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
R0024.0 38 35 5.8–14.9 409 S
DOUBLES
Star R.A. Dec. P.A. Sep. Mags
hm °’ ° “
Á 02 03.9 42 20 063 9.8 2.3, 4.8 B is a binary, 61y;
5.5, 6.3; sep 0”.5
CLUSTERS AND NEBULAE
M C NGC R.A. Dec. Mag. Dimensions Type
h m ° ’ ’
31 224 00 42.7 41 16 3.5 178 63 Sb galaxy. Great.
32 221 00 42.7 40 52 8.2 7.6 5.8 E2 galaxy. Com toM31.
205 00 40.4 41 41 8.0 17.4 9.8 E6 galaxy. Com to M31.
752 01 57.8 37 41 5.7 50 Open cluster
22 7662 23 25.9 42 33 9.2 20” 130” Planetary nebulaBRIGHTEST STARS
No. Star R.A. Dec. Mag. Spectrum Proper name
hm s ° ‘ “
4 ‚ 02 09 32 34 59 14 3.00 A5
Also above magnitude 4.3: ·(Rasalmothallah) (3.41), Á(4.01).
VARIABLES
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
R0237.0 34 16 5.4–12.6 Mira 266.5
GALAXY
M NGC R.A. Dec. Mags Dimensions Type
hm °‘ ‘
33 598 01 33.9 30 39 5.7 62 39 Sc galaxyBRIGHTEST STARS
No. Star R.A. Dec. Mag. Spectrum Proper name
hm s ° ‘ “
13 · 02 07 10 23 27 45 2.00 K2 Hamal
6 ‚ 01 54 38 20 48 29 2.64 A5 Sheratan
Also above magnitude 4.3: 41 (c) (Nair al Butain) (3.63), Á(Mesartim) (3.9) (combined magnitude).
VARIABLES
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
R0024.0 38 35 5.8–14.9 409 S
DOUBLES
Star R.A. Dec. P.A. Sep. Mags
hm °’ ° ”
Á 01 53.5 19 18 000 7.8 4.8, 4.8BRIGHTEST STARS
No. Star R.A. Dec. Mag. Spectrum Proper name
hm s ° ‘ “
33 · 03 24 19 49 51 40 1.80 F5 Mirphak
26 ‚ 03 08 10 40 57 21 2.12 (max) B8 Algol
44 ̇ 03 54 08 31 53 01 2.85 B1 Atik
45 Â 03 57 51 40 00 37 2.89 B0.5
23 Á 03 04 48 53 30 23 2.93 G8
39 ‰ 03 42 55 47 47 15 3.01 B5
25 Ú 03 05 10 38 50 25 3.2 (max) M4 Gorgonea Terti
Also above magnitude 4.3: Ë(Miram) (3.76), Ó(3.77), Î(Misam) (3.80), Â(3.83), Ù(Kerb) (3.85), ̆(Nembus) (4.04),
Í (Menkib) (4.04), È(4.05), Ê(4.07), ı(4.12), Ì(4.14), „(4.23), 16 (4.23), 16 (4.23), Ï(4.29).
VARIABLES
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
‚ 03 08.2 40 57 2.1–3.4 Algol 2.87 BG
Ú 03 05.2 38 50 3.2–4.2 Semi-reg. 33/55 M
X 03 55.4 31 03 6.0–7.0 Irregular - X-ray
source
DOUBLES
Star R.A. Dec. P.A. Sep. Mags
hm °’ ° “
Ë 02 50.7 55 54 300 28.3 3.3,8.5
CLUSTERS AND NEBULAE
M NGC R.A. Dec. Mag. Dimensions Type
hm °’ ’
34 1039 02 42.0 42 47 5.2 35 Open cluster
76 650-1 01 42.4 51 34 12.2 65” 290” Planetary nebulaANDROMEDATRIANGULUMARIESPERSEUSGb Atl of Univ Phil'03stp 2/4/03 7:41 pm Page 241