Polaris A, the supergiant primary component, is a classic Population I Cepheid variable, although it was once thought to be Population II due to its high galactic latitude. Since Cepheids are an important standard candle for determining distance Polaris, as the closest such star, is heavily studied. The variability of Polaris had been suspected since 1852; this variation was confirmed by Ejnar Hertzsprung in 1911.
Both the amplitude and period of the variations have changed since discovery. Prior to 1963 the amplitude was over 0.1 magnitude and decreasing very gradually. After 1966 it decreased very rapidly until it was less than 0.05 magnitude and since then has varied erratically near that range. It has been reported that the period is now increasing. The period increased fairly steadily by around 4 seconds per year until 1963. It then stayed constant for 3 years, but began to increase again from 1966 onwards. Current measurements show a consistent increase of 3.2 seconds per year in the period. This was originally thought to be due to secular red-ward evolution across the instability strip, but is now considered to be interference between the primary and first overtone pulsation modes. Comparison of the period luminosity relationship and the observed luminosity indicate that the main pulsations are the first overtone.
Research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, changing from third to its current second magnitude. Astronomer Edward Guinan considers this to be a remarkable rate of change and is on record as saying that "If they are real, these changes are 100 times larger than predicted by current theories of stellar evolution."
Read more about this topic: Polaris
Other articles related to "variable star, star, stars":
... Peltier Award in 1981 for his variable star and lunar occultation observations and contributions to artificial satellite programs ... The American Association of Variable Star Observers honoured him with the Merit Award in 1988, for his record of more than 50,000 observations in the AAVSO ... Achievement Award of the Astronomical Society of the Pacific for his variable star and occultation observations in 1997 ...
... The star system was discovered in 1948 by Willem Jacob Luyten in the course of compiling a catalog of stars of high proper motion he noted its exceptionally high proper motion of 3.37 ... The two stars are of nearly equal brightness, with visual magnitudes of 12.57 and 11.99 as seen from Earth ... The distance between the two stars varies from 2.1 to 8.8 astronomical units (310 to 1,320 Gm) ...
... Stars with planets may also show brightness variations if their planets pass between the earth and the star ...
... The novel Variable Star was written by Spider Robinson based on an outline created by Heinlein and found after his death ...
... Despite its size, Hydra contains only one reasonably bright star, Alphard, designated Alpha Hydrae ... Beta Hydrae is a blue-white star of magnitude 4.3, 365 light-years from Earth ... Hydra has one bright binary star, Epsilon Hydrae, which is difficult to split in amateur telescopes it has a period of 1000 years and is 135 light-years from Earth ...
Famous quotes containing the words star and/or variable:
“It is the star to every wandring bark,
Whose worths unknown, although his height be taken.
Loves not Times fool, though rosy lips and cheeks
Within his bending sickles compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.”
—William Shakespeare (15641616)
“Walked forth to ease my pain
Along the shore of silver streaming Thames,
Whose rutty bank, the which his river hems,
Was painted all with variable flowers,”
—Edmund Spenser (1552?1599)