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Delta (δ) Cephei
Optical Double Star
| Right Ascension | 22h 29m 9.7s | Best Seen | 7/15 - 2/15 |
| Declination | 58° 24' 35" | Combined Magnitude | 3.94 |
| Apparent Separation | 42.7" | Constellation | Cepheus |
Actual |
Compared to Sun |
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| Distance | 982 / 950 ly | -- |
| Actual Brightness | -- | 1682 / 200 |
| Magnitude | 3.5 to 4.3 / 6.31 | -- |
| Mass | -- | 5 / ? |
| Surface Gravity | -- | -- |
| Surface Composition (by mass) | 74% hydrogen 24% helium 2% everything else |
same |
| Spectral Type | F5 I to G2 I | G2 V |
| Density (gram/cubic cm) | -- | -- |
What To Look For Through The Telescope
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Recommended eyepiece: 24mm or 40 mm.
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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:
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The dimmer star may be part of a multiple system.
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The brighter star is the namesake of “Cepheid variable” stars.
a. Cepheids are dying, high-mass stars.
b. Cepheid stars pulsate.
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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.
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As a result, their surface temperatures vary.
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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.
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The first Cepheid variable star discovered was actually Eta Aquila.
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Two people associated with delta Cephei and Cepheid variables faced many challenges.
a. John Goodricke, from England, discovered delta Cephei in 1784.
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He had been deaf and mute since infancy.
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Despite normal treatment of people with such handicaps, his parents made sure he received an education. He excelled in math and astronomy.
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He received an award from the Royal Society of London in 1783 for determining the period and cause of variation of the star Algol (Beta β Persei).
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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.
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At that time, women couldn’t even vote.
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Women were hired to do astronomy, but they were hired to do the “grunt work,” reducing great amounts of data.
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As a result of working so closely with the data, women contributed to many discoveries in astronomy, yet rarely received any credit.
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References
| Item | Updated | Notes |
| Coordinates | 2002-11-27 | split the difference between the two, with Scott’s The Flamsteed Collection and SIMBAD |
| Combined Magnitude | 2002-11-27 | from Scott’s The Flamsteed Collection |
| Apparent Separation | 2002-11-27 | from coordinates from Flamsteed |
| Distance | 2002-11-27 | SIMBAD and Flamsteed |
| Actual Brightness | 2002-11-27 | Flamsteed |
| Magnitude | 2002-11-27 | Flamsteed and http://www.astro.uiuc.edu/~kaler/sow/deltacep.html |
| Mass | 2002-11-27 | http://www.astro.uiuc.edu/~kaler/sow/deltacep.html |
| Surface Gravity | -- | |
| Surface Composition | 2003-01-06 | OK for all stars |
| Spectral Type | 2002-11-27 | SIMBAD and http://www.astro.uiuc.edu/~kaler/sow/deltacep.html |
| Density | -- | |
| Other Information | 2002-11-27 | 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 |