|Alpha Cygni Variables
||Blue or white supergiant stars, typified by Alpha Cygni or Deneb in Cygnus, showing complex patterns of overlaid oscillations that form a regular cycle. The cycle takes at least several days, and sometimes weeks, to repeat.
|Beta Cephei Variables
||Hot stars of the B-type and O-type spectral classifications, Beta Cephei variables typically swell and contract over a period of less than a day, with the star emitting most light energy as it reaches its minimum diameter. Most variables of this type are of the radial type, but there are a few rare non-radial examples.
|Cepheid or Delta Cephei Variables
|Supergiant stars of which Delta Cephei is a prominent example, and the source of the name Cepheid. The magnitude of Cepheid variables typically varies over periods of dozens of days and, crucially, this period correlates closely with the luminosity of the star. This relationship means that the period of a given Cepheid variable can be used to accurately calculate its distance.
|Cepheid or Delta Cephei Variables
|These variables are related to the classical or Type I Cepheids, though typically rather less luminous and following shorter periods of pulsation. Like classical Cepheids, these stars also show a relationship between their luminosity and their period of variability.
|Delta Scuti Variables
||Variable stars that follow a complicated pattern of radial and non-radial pulsations, so that in some cases different parts of the star may be expanding or contracting concurrently. Like Cepheids, Delta Scuti variables show a relationship between their period and their luminosity, allowing their distance to be calculated with considerable accuracy.
|Gamma Doradus Variables
||A relatively rare variable type whose members are typically white or bright yellow dwarf stars, and whose variability is caused by gravity waves within the star's structure. The pulsations of Gamma Doradus variables typically follow a period a few hours, and are rarely longer than a day apart.
||Named for their prototype, Mira in Cetus, these are red giant stars in the last stages of their lives. Mira variables can show extreme variations in magnitude (for example Mira itself varies between a relatively bright +2 and an extremely faint +10). Variables of this kind typically have periods running into hundreds of days in length.
|PV Telescopii Variables
||A rare class of variables, typically blue supergiants with notably high levels of carbon in their structure. Stars of this kind commonly show shifts in brightness over a period of less than a day, but much longer patterns of variability can also occur.
|RR Lyrae Variables
||These are old, low-mass stars (typically about half the mass of the Sun) that are commonly found in the globular clusters surrounding the Milky Way Galaxy (and indeed other galaxies). Like Cepheids, their pattern of pulsation - in this case in the infrared - provides a 'standard candle' for the calculation of their distance.
|RV Tauri Variables
||A group of exceptionally luminous stars whose colour shifts alongside their brightness. A typical variable of this type will shine with a red or orange light at its miminum brightness, but as it undergoes radial expansion its brightness increases and its spectrum shifts towards the yellow. The cycles between peak magnitude for these stars can take several months to complete.
||A populous and diverse group of variable stars characterised by the fact that, while their variability shows a regular pattern of pulsation, their luminosity can also shift unpredictably within that underlying pattern (which can take years to recur). Stars belonging to this extensive group are usually giants or supergiants, and are divided into five further subcategories based on the details of their variability.
|SX Phoenicis Variables
||A variant of the Delta Scuti variable type, but showing more rapid variations in brightness (over periods of minutes of hours). SX Phoenicis variables are typically older stars of the dwarf or subdwarf types, commonly found outside the main disc of the Milky Way in the surrounding galactic halo or in globular clusters.
|ZZ Ceti Variables
||A class of variable white dwarfs that show non-radial shifts in brightness taking place over periods of seconds or minutes. Stars of this kind are occasionally observed to show sudden flares in brightness, though it is uncertain whether this is due to the underlying pulsing mechanism.