HD 209458 is an 8th- magnitude

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

. It is a G0V star, and is thus very similar to the Sun. Because it is located at a distance of about 159

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s, it is not visible to the unaided eye. With good

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

or small

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

it should be easily detectable. V376PegLightCurve

In 1999, two teams working independently (one team consisted of astronomers at the Geneva Observatory, the Center for Astrophysics Harvard & Smithsonian, and the Wise Observatory; the second group was the

California and Carnegie Planet Search California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

team) discovered an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting the star by using the

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

search method. Soon after the discovery, separate teams led by David Charbonneau and Gregory W. Henry were able to detect a

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

of the planet across the surface of the star making it the first known transiting extrasolar planet. The planet received the designation '' HD 209458 b''. Because the planet transits the star, the star is dimmed by about 2% every 3.5 days making it an extrinsic variable. The

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

designation for HD 209458 is V376 Pegasi. It is the

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and software programming. A prototype is generally used to ...

of the variable class "EP" in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

, defined as stars showing eclipses by their planets.

Planetary system

HD 209458 b is an extrasolar planet that orbits the Sun-like star HD 209458 in the constellation Pegasus.

Spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

studies first revealed the presence of a planet around HD 209458 on November 5, 1999. The planet is now under even more public scrutiny with the announcement that its atmosphere contains water vapor. Astronomers had made careful photometric measurements of several stars known to be orbited by planets, in the hope that they might observe a dip in brightness caused by the

of the planet across the star's face. This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected. Travis Barman at Lowell Observatory in Flagstaff, Arizona analyzed the emission spectrum of this planet in 2009, and believes that its atmosphere contains water, although previous research in 2007 suggests that the atmosphere is composed mostly of silicate clouds. The spectrum taken in 2020 did indeed feature either sodium or vanadium oxide, but not the water. Later study in 2021 did not find any planetary atmosphere at all.

References

External links

* {{DEFAULTSORT:HD 209458 209458 108859 Pegasus (constellation) Planetary transit variables Planetary systems with one confirmed planet G-type main-sequence stars Pegasi, V376 Durchmusterung objects J22031077+1853036