Perseus

Immediately to the west of Auriga is another interesting constellation, Perseus. It contains no first-magnitude star but has an interesting binary star which can be fun to observe, and numerous star clusters. The brightest star in the constellation is Alpha Persei, or Mirphak (mag. 1.8), which is at a distance of about 190 light-years from us. It lies within a scattered cluster of fainter stars which is fun watching through a pair of binoculars. We can easily locate it by extending the line joining the two northern stars of Pegasus (see page 85) and the three principal stars of Andromeda eastward.

The star Beta Persei, which we can see soutn of Mirphak, is one of the most fascinating star** in the sky. It is also known as Algol, which means the 'Winking Demon', for its periodic change in brightness. It is one of those stars astronomers call 'eclipsing variables'. For two days and

Time exposure showing trails of circumpolar stars.
Orion Nebula (M42).
Crab Nebula (Ml) in Taurus.
Globular cluster (M13) in Hercules.
North America Nebula in Cygnus.
Andromeda Galaxy (M31).
The Milky Way.

eleven hours, Algol shines steadily as an ordinary star of magnitude 2.3. Then in a period of about four hours, it gets fainter to magnitude 3.5. After remaining dim for only 20 minutes, it brightens up again to its original brilliance

Perseus

Star

Name

Magnitude

Distance

(Light-years)

a

Mirphak

1.80

620

P

Algol

2.3-3.5

95

y

2.93

143

C

Atik

2.85

1011

e

2.89

678

5

3.01

326

in about four hours, and the cycle continues. If the sky is absolutely clear, we may be lucky to observe both the dimming and brighten?ng phases in a single night (as winter nights are pretty long) and it is a thrilling experience. Algol winks' because it is actually made up of two stars revolving

Perseus.

around each other, one of them being much brighter than the other. When the fainter star comes between us and the brighter star, Algol seems to be dimmed. As it moves away, Algol brightens up again.

Among the other interesting objects in Perseus are numerous star clusters, as many as 11 of which can be seen with any medium-power telescope. This is not surprising, as the Milky Way forms the background for most of the constellation. Two of the clusters, named NGC 859 and NGC 884, are quite bright and are visible to the unaided eye on dark nights, appearing as faint symmetrical spots lying between the constellation of Cassiopeia and the star Mirphak. The two clusters form the 'Sword Handle' of Perseus and can be seen separately wi±h a pair of good binoculars or a medium-power telescope. Each of the two clusters contains more than 300 stars. For viewers in southern parts of India, however, these two clusters will be difficult objects to see as they are too far north in the sky. Perseus culminates at around 9.00 p.m. during the last week of December.

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