• Science • People
Non User
 • Locations • Timeline
Index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Home > Variable star

 
Most stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0.1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminosity, and these are known as variable stars. Variable stars may either intrinsic or extrinsic.

1 Double star observations

Double stars are generally analysed using photometry and photospectrometry . Observations of their brightness compared to non-variable stars of known magnitude can be used to establish a light curve. For regular variables, the period of variation and its amplitude can be very well established; for many variable stars, though, these quantities may vary slowly over time, or even from one period to the next. Peak brightnesses in the light curve are known as maxima, while troughs are known as minima.

2 Intrinsic variables

These are stars which have intrinsic variations in brightness, that is the star itself gets brighter and dimmer. This category can itself be divided into two subgroups: pulsating and cataclysmic (or eruptive) variables. Examples of types within these divisions are given below.

2.1 Pulsating variables

2.1.1 Cepheid variables

Main article: Cepheid variable

One of the most important types of variables star are Cepheid variables, yellow giant stars which undergo pulsations with very regular periods. They are named after Delta Cephei , the first of the class to be discovered, and have periods ranging from about a day to several weeks.

Cepheids are important because they are a type of standard candle. Their luminosity is directly related to their period of variation, with a slight dependence on metallicity as well. The longer the pulsation period, the more luminous the star. Once this period-luminosity relationship is calibrated, this means that by observing the periods of Cepheids, their luminosity can be established. Their distance is then easily found from their apparent brightness. Observations of Cepheid variables are very important for determining distances to galaxies within the Local Group.

2.1.2 W Virginis stars

These are very similar to Cepheids, but belong to Population II and so have a lower metallicity and hence a slightly different period-luminosity relationship.

2.1.3 δ Scuti stars

These are similar to Cepheids but rather fainter, and with shorter periods. They were once known as Dwarf Cepheids. They often show many superimposed periods, which combine to form an extremely complex light curve.

2.1.4 RR Lyrae stars

These stars are somewhat similar to Cepheids, but are not as luminous. They are older than cepheids, belonging to Population II. They are common in globular clusters, and were occasionally referred to in the past as cluster Cepheids. They also have a well established period-luminosity relationship, and so are also useful distance indicators.

2.1.5 RV Tauri stars

These are yellow supergiant stars which have alternating deep and shallow minima. This double-peaked variation typically has periods of 30-100 days. Superimposed on this variation, there may be long-term variations over periods of several years.

2.1.6 Mira variables

Mira variables are very cool red supergiants, which are undergoing very large pulsations. Over periods usually of many months, they may brighten by several magnitudeThe apparent magnitude m of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object. Hundred times less bright (e. the same object ten times as far) corresponds to an apparent mas before fading again. MiraMira Omicron Ceti, is an oscillating variable star. The first non- supernova variable star discovered, excepting the odd Eta Carinae, it is the brightest periodic variable in the sky that is not visible during part of its cycle. Mira was discovered (or at itself, also known as Omicron Ceti, varies in brightness from almost 2nd magnitude to as faint as 9th magnitude.

Read more »

Topics: Variable Star, Double Star Observations, Intrinsic Variables...

Variable star designationVariable stars are named using a variation on the Bayer designation format of Identifier . In previous centuries few variable stars were known, so it seemed reasonable to use the letters of the Roman alphabet, starting from the letter R so as to avoid conVariableIn computer science and mathematics, a variable is a symbol denoting a quantity or symbolic representation. In mathematics, a variable often represents an unknown quantity; in computer science, it represents a place where a quantity can be stored. VariablVariable specific impulse magnetoplasma rocketVariable specific impulse magnetoplasma rockets or VASIMRs as the name is commonly abbreviated is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields to accelerate a propellant. VASIMRs bridge the gap between high- thrus
Variable length bufferIn telecommunication, a variable length buffer is a buffer into which data may be entered at one rate and removed at another rate without changing the data sequence. Note: Most first-in first-out (FIFO) storage devices are variable-length buffers in thatVariable starMost stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0. 1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminVariable bit rateThe term variable bit rate VBR is a term in telecommunications Quality of Service. Compare with constant bit rate. An MP3 file can be recorded with a variable bitrate from 8 320 Kbit to save memory. When referring to codecs, variable bit rate encoding var
Variable pricingVariable message signVariable fighter
Variable SkinkVariable area meterVariable Sunbird
Variable universal life insuranceVariable number tandem repeatsVariable argument macro
Non User