DELTA (δ) CEPHEI
OPTICAL DOUBLE STAR

Right Ascension:
22h 29m 9.7s

Best Seen:
7/15 - 2/15

Declination:
58º 24' 35" Combined
Magnitude:
3.94

Computer File:
deltacep

Constellation:
Cepheus

Apparent
Separation: 42.7"

Actual

Compared to Sun

Distance

982 / 950 l.y.

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Actual Brightness

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1682 / 200

Magnitude

3.5 to 4.3 / 6.31

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Mass

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5 / ?

Surface Gravity

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Surface Composition (by mass)

74% hydrogen 24% helium 2% everything else

same

Spectral Type

F5 I to G2 I / A0

G2 V

Density (gram/cubic cm)

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WHAT TO LOOK FOR THROUGH THE TELESCOPE:

  1. Recommended eyepiece: 24mm or 40 mm.

  2. When people look through the telescope they should see two stars next to each other. One star should be slightly brighter than the other.

DELTA CEPHEI INFORMATION:

  1. The dimmer star may be part of a multiple system.

  2. The brighter star is the namesake of “Cepheid variable” stars.

a. Cepheids are dying, high-mass stars.

b. Cepheid stars pulsate.

  1. Gas pressure makes star expand... a bit too far, then gravity takes over and makes star contract... a bit too far, then gas pressure expands star, etc.

  2. As a result, their surface temperatures vary.

  3. Because of the expansion and contraction, their brightness varies.

c. The period of expansion and contraction, and therefore the change in brightness, is very regular, like the tick of a clock.

d. There is a direct relationship between the period and brightness of Cepheids.

e. From this information, the distance to the Cepheid variable can be found.

f. Cepheids are so luminous they can easily be found in other galaxies, so the distance to galaxies can be determined by looking at these Cepheid variable stars.

  1. The first Cepheid variable star discovered was actually Eta Aquila.

  2. Two people associated with delta Cephei and Cepheid variables faced many challenges.

a. John Goodricke, from England, discovered delta Cephei in 1784.

  1. He had been deaf and mute since infancy.

  2. Despite normal treatment of people with such handicaps, his parents made sure he received an education. He excelled in math and astronomy.

  3. He received an award from the Royal Society of London in 1783 for determining the period and cause of variation of the star Algol.

  4. He died at the age of 21 from a bout of pneumonia, apparently caught while observing delta Cephei in 1786.

b. Henrietta Swan Leavitt recognized the Period-Luminosity relationship in 1912.

  1. At that time, women couldn’t even vote.

  2. Women were hired to do astronomy, but they were hired to do the “grunt work,” reducing great amounts of data.

  3. As a result of working so closely with the data, women contributed to many discoveries in astronomy, yet rarely received any credit.

Previously...

  1. In 2,000 years, this star will be the pole star.

HOWEVER, have only found that gamma Cephei will be the pole star, not delta http://starryskies.com/The_sky/constallations_html/cepheus.html and http://www.dibonsmith.com/cep_con.htm

Item
Updated Notes

Coordinates 11-27-2002
split the difference between the two, with Scott’s The Flamsteed Collection and SIMBAD

Combined Magnitude
11-27-2002
from Scott’s The Flamsteed Collection

Apparent Separation 11-27-2002
from coordinates from Flamsteed

Distance
11-27-2002
SIMBAD and Flamsteed

Actual Brightness
11-27-2002
Flamsteed

Magnitude
11-27-2002
Flamsteed and http://www.astro.uiuc.edu/~kaler/sow/deltacep.html

Mass
11-27-2002
http://www.astro.uiuc.edu/~kaler/sow/deltacep.html

Surface Gravity

Surface Composition 01-06-2003
OK for all stars

Spectral Type
11-27-2002
SIMBAD and http://www.astro.uiuc.edu/~kaler/sow/deltacep.html

Density

Other Information
11-27-2002
http://www.astro.uiuc.edu/~kaler/sow/deltacep.html and http://www.aavso.org/vstar/vsotm/0900.stm and http://www.seds.org/~spider/spider/Vars/deltaCep.html and