Last month I profiled three classic variable stars prominently visible in fall (Delta Cephei
, Mira, and Algol) and mentioned that three of the 20th century's greatest amateur astronomers were avidly enthusiastic variable star observers.
Examples of this behaviour are classified as delta Cephei
, RR Lyrae and delta Scuti stars according to their position in the H-R diagram and the nature of their variation.
The star in the study is Delta Cephei
, which is the namesake for the entire class of Cepheids and was discovered in 1784.
I wrote about Delta Cephei
in last October's installment of this column.
It is also home to two important variable stars; delta Cephei
, prototype of the Cepheid variables, and mu Cephei, the semi-regular Garnet Star named by Sir William Herschel and one of the reddest naked eye stars in the sky (although this is totally lost on the colour-blind Director).
In last month's column I argued that Cepheus was underrated and described wonders in the Cepheus Milky Way's "spur to Kurhah" and "Delta Cephei
triangle." But there's more in Cepheus: the oldest and most northerly open star cluster NGC 188; the Cepheus-Cygnus border "odd couple," galaxy NGC 6946 and open cluster NGC 6939; and yet another lovely double star Beta ((3) Cephei (Alfirk).
John Coodricke discovered the variability of Delta Cephei
, the prototype of the class, in 1784.
is a yellow-giant star that changes from magnitude 3.5 to 4.4 and back over 5.4 days.
Extended cocoons of gas resolved around the Cepheid variables Polaris and Delta Cephei
suggest a connection between these stars' pulsations and the shedding of mass, with far-reaching implications.
Using the Very Large Telescope Interferometer in Chile and the CHARA Array on California's Mount Wilson, an international team resolved infrared cocoons around Polaris, Delta Cephei
, and L Carinae.
Though the archetype Cepheid variable, Delta Cephei
, lies too far north for most Southern Hemisphere observers, a good substitute rides high on the meridian at this time of year: Kappa (k) Pavonis.
It is a Cepheid variable, meaning it belongs to the important class named after Delta Cephei
. (That star's fluctuations were first detected in 1784 by English amateur John Goodricke, another great pioneer of variable-star astronomy.)