proper motion

Normally when the Earth and Venus are in conjunction they are not aligned with the Sun. Venus' orbit is inclined by 3.4° to the Earth's so it appears to pass under (or over) the Sun in the sky. Transits occur when the two planets happen to be in conjunction at (or very near) the points where their orbital planes cross. Although 3.4° may not seem like much, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction. Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

Read more here: » Transit of Venus: Encyclopedia II - Transit of Venus - Conjunctions of Venus with the Sun

The simultaneous occurrence of a transit of Mercury and a transit of Venus is possible, but only in the distant future. Such an event will next occur only in the years 69163 and 224508. The simultaneous occurrence of a solar eclipse and a transit of Venus is currently possible, but very rare. The next solar eclipse occurring during a transit of Venus will be on April 5 15232. Only 5 hours after the transit of Venus on June 4, 1769 there was a total solar eclipse, which was visible in Northern America, Europe and Northern Asia almost as partial solar eclipse. This was the lowest time difference between a trans ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

Read more here: » Transit of Venus: Encyclopedia II - Transit of Venus - Simultaneous transits

In many cultures of the world, the transit of Venus across the Sun has been regarded as a rare and therefore an important event that marks major changes in human history. This is true for the Maya and other ancient American civilizations, for the Indian Vedic traditions and for the Western astrology of Mesopotamian origin. It has been claimed that a transit led to the ancient Greeks celebrating the Ancient Olympics every four years as a form of commemoration. The efforts of Guillaume Le Gentil to observe the transit of Venus in different parts of the globe, became the subject of the fictiona ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

Read more here: » Transit of Venus: Encyclopedia II - Transit of Venus - Cultural meaning

Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary system, composed of two K class (orange) main sequence stars, 61 Cygni A and 61 Cygni B. The brighter star 61 Cygni A is of apparent magnitude 5.2, the fainter 61 Cygni B is 6.1. The two orbit their common barycenter in a period of 653.2 years. An observer using 7×50 binoculars can find 61 Cygni two binocular fields south-east of the bright star Deneb. An observer using larger binoculars, or a telescope, will be able to resolve the two components of the binary. See also:

61 Cygni, 61 Cygni - General information, 61 Cygni - The binary system, 61 Cygni - 61 Cygni B's planet, 61 Cygni - 61 Cygni in Fiction

Read more here: » 61 Cygni: Encyclopedia II - 61 Cygni - The binary system

One question raised by the detection of extrasolar planets is why so many of the detected planets are gas giants which, in comparison to Earth's solar system, are unexpectedly close to the orbited star. For example, τ Boötis has a planet 4.1 times Jupiter's mass, which is less than a quarter of an astronomical unit (AU) from the orbited star, which is closer to the star than Mercury orbits the sun. HD 114762 has a planet 11 times Jupiter's mass which is less than half an AU from the orbited star. The reason for these relatively extreme pla ...

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Extrasolar planet, Extrasolar planet - History of detection, Extrasolar planet - Methods of detection, Extrasolar planet - Pulsar timing, Extrasolar planet - Astrometry, Extrasolar planet - Radial velocity, Extrasolar planet - Gravitational microlensing, Extrasolar planet - Transit method, Extrasolar planet - Circumstellar disks, Extrasolar planet - Direct observation, Extrasolar planet - Solar system formation processes, Extrasolar planet - Notable extrasolar planets, Extrasolar planet - Table of extremes

Read more here: » Extrasolar planet: Encyclopedia II - Extrasolar planet - Solar system formation processes

See the list of stars with confirmed extrasolar planets for a list of confirmed observations. Extrasolar planet - Table of extremes. Note: upper limit for planets is 11 MJupiter (deuterium fusion limit) Note: PSR 1257+12 system may include possible asteroidal object, but it is not massive enough to qualify as a planet Note: only radii of transiting planets are known Note: unconfirmable planet in the line of ...

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Extrasolar planet, Extrasolar planet - History of detection, Extrasolar planet - Methods of detection, Extrasolar planet - Pulsar timing, Extrasolar planet - Astrometry, Extrasolar planet - Radial velocity, Extrasolar planet - Gravitational microlensing, Extrasolar planet - Transit method, Extrasolar planet - Circumstellar disks, Extrasolar planet - Direct observation, Extrasolar planet - Solar system formation processes, Extrasolar planet - Notable extrasolar planets, Extrasolar planet - Table of extremes

Read more here: » Extrasolar planet: Encyclopedia II - Extrasolar planet - Notable extrasolar planets

Open clusters range from very sparse clusters with only a few members to large agglomerations containing thousands of stars. They usually consist of quite a distinct dense core, surrounded by a more diffuse 'corona' of cluster members. The core is typically about 3–4 light years across, with the corona extending to about 20 light years from the cluster centre. Typical star densities in the centre of a cluster are about 1.5 stars per cubic light year (the stellar density near the sun is about 0.1 star per cubic light year) ^{See also:}

Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

Read more here: » Open cluster: Encyclopedia II - Open cluster - Morphology and classification

All stars are originally formed in multiple systems, because only a cloud of gas containing many times the mass of the Sun will be heavy enough to collapse under its own gravity, but such a heavy cloud cannot collapse into a single star. The formation of an open cluster begins with the collapse of part of a giant molecular cloud, a cold dense cloud of gas containing up to many thousands of times the mass of the Sun. Many factors may trigger the collapse of a giant molecular cloud (or part of it) and a burst of star formation which wil ...

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Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

Read more here: » Open cluster: Encyclopedia II - Open cluster - Formation

Because open clusters tend to be dispersed before most of their stars reach the end of their lives, the light from them tends to be dominated by the young, hot blue stars. These stars are the most massive, and have the shortest lives of a few tens of millions of years. The older open clusters tend to contain more yellow stars. Some open clusters contain hot blue stars which seem to be much younger than the rest of the cluster. These blue stragglers are also observed in globular clusters, and in the very dense cores of globulars they a ...

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Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

Read more here: » Open cluster: Encyclopedia II - Open cluster - Stellar composition

Many open clusters are inherently unstable, with a small enough mass that the escape velocity of the system is lower than the average velocity of the constituent stars. These clusters will rapidly disperse within a few million years. In many cases, the stripping away of the gas from which the cluster formed by the radiation pressure of the hot young stars reduces the cluster mass enough to allow rapid dispersal. Clusters which have enough mass to be gravitationally bound once the surrounding nebula has evaporated can remain distinct f ...

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Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

Read more here: » Open cluster: Encyclopedia II - Open cluster - Eventual fate

When a Hertzsprung-Russell diagram is plotted for an open cluster, most stars lie on the main sequence. The most massive stars have begun to evolve away from the main sequence and are becoming red giants, the position of the turn-off from the main sequence can be used to estimate the age of the cluster. Because the stars in an open cluster are all at roughly the same distance from Earth, and were born at roughly the same time from the same raw material, the differences in apparent brightness among cluster members is due only to their ...

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Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

Read more here: » Open cluster: Encyclopedia II - Open cluster - Studying stellar evolution

A variety of data can be observed for each star. The position coordinates locate the star on the sky using the techniques of spherical astronomy, and the magnitude determines its brightness as seen from the Earth. The relative brightness in different parts of the spectrum yields information about the temperature of the star, as well as certain properties of its photosphere. Photographs of the sp ...

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Observational astronomy, Observational astronomy - Unaided eye, Observational astronomy - Telescopes, Observational astronomy - Optical telescopes, Observational astronomy - Other instruments, Observational astronomy - Observation tools, Observational astronomy - Observing, Observational astronomy - Related lists

Read more here: » Observational astronomy: Encyclopedia II - Observational astronomy - Observing

In addition to examination of the universe in the optical spectrum, astronomers have increasingly been able to acquire information in other portions of the electromagnetic spectrum. The earliest such non-optical measurements were made of the thermal properties of the Sun. Instruments employed during a solar eclipse could be used to measure the radiation from the corona. With the discovery of radio waves, radio astronomy began to emerge as a new discipline in astronomy. The long wavelengths of radio waves required much larger collectin ...

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Observational astronomy, Observational astronomy - Unaided eye, Observational astronomy - Telescopes, Observational astronomy - Optical telescopes, Observational astronomy - Other instruments, Observational astronomy - Observation tools, Observational astronomy - Observing, Observational astronomy - Related lists

Read more here: » Observational astronomy: Encyclopedia II - Observational astronomy - Other instruments

In the fictional Star Trek universe, the Triangulum Galaxy is where the USS Enterprise is warped to after a being known as The Traveler uses his powers to influence the ship's warp drive. M33 is said to be approximately 2.7 million light years away from the United Federation of Planets territories. The galaxy was first encountered in the Star Trek: The Next Generation episode "Where No One Has Gone Before." On Gene Roddenberry's Andromeda the Systems Commonwealth had territory in the Triangulum ...

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Triangulum Galaxy, Triangulum Galaxy - General information, Triangulum Galaxy - References in fiction, Triangulum Galaxy - External link

Read more here: » Triangulum Galaxy: Encyclopedia II - Triangulum Galaxy - References in fiction

Beyond the visible, inner portion of the galactic halo lies a much larger region, known as the dark halo, extended halo or galactic corona, which contains large amounts of dark matter. The presence of dark matter in the halo is demonstrated by its gravitational effect on a spiral galaxy's rotation curve. Without large amounts of mass in the extended halo, the rotational velocity of the galaxy should decrease at large distance from the galactic core. However, observations of spiral galaxies, particularly radio observations of line emis ...

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Galactic halo, Galactic halo - Halo stars, Galactic halo - Halo dark matter

Read more here: » Galactic halo: Encyclopedia II - Galactic halo - Halo dark matter

Prior to the discovery of the telescope, early observational astronomy relied upon the unaided eye and various instruments for measuring time and direction. Tycho Brahe is noted for his systematic observations of the heavens, and the data he collected was used by Johannes Kepler to build his laws of planetary motion. The heavens have been regarded by humans for much of recorded history. Ancient stone structures were built as a means of measuring the passage of time based on the movements of the Sun. Constellations were specific patterns of stars in the sky that came to be associated with particular se ...

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Observational astronomy, Observational astronomy - Unaided eye, Observational astronomy - Telescopes, Observational astronomy - Optical telescopes, Observational astronomy - Other instruments, Observational astronomy - Observation tools, Observational astronomy - Observing, Observational astronomy - Related lists

Read more here: » Observational astronomy: Encyclopedia II - Observational astronomy - Unaided eye

Galileo Galilei was the first person to known to turn a telescope to the heavens and to record what he saw. Since that time, observational astronomy has made steady advances with each improvement in telescope technology. A traditional division of observational astronomy is given by the region of the electromagnetic spectrum observed: Optical astronomy is the part of astronomy that uses optical components (mirrors, lenses and solid-state detectors) to observe light from near infrared to near ultraviolet wavelengths. Visibl ...

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Observational astronomy, Observational astronomy - Unaided eye, Observational astronomy - Telescopes, Observational astronomy - Optical telescopes, Observational astronomy - Other instruments, Observational astronomy - Observation tools, Observational astronomy - Observing, Observational astronomy - Related lists

Read more here: » Observational astronomy: Encyclopedia II - Observational astronomy - Telescopes

For much of the history of observational astronomy, almost all observation has been performed in the visual spectrum with optical telescopes. While the Earth's atmosphere is nearly completely transparent in this portion of the electromagnetic spectrum, most telescope work is still dependent on seeing conditions and is generally restricted to the night time. The seeing conditions depend on the depth, movement, and clarity of the air. Locations that are frequently cloudy or suffer from atmospheric turbulence restrict detailed observation. Likewise the presence of the full Moon ca ...

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Observational astronomy, Observational astronomy - Unaided eye, Observational astronomy - Telescopes, Observational astronomy - Optical telescopes, Observational astronomy - Other instruments, Observational astronomy - Observation tools, Observational astronomy - Observing, Observational astronomy - Related lists

Read more here: » Observational astronomy: Encyclopedia II - Observational astronomy - Optical telescopes

In his later career, Herschel discovered two satellites of Saturn, Mimas and Enceladus; as well as two satellites of Uranus, Titania and Oberon. He did not give these satellites their names; rather, they were named by his son John in 1847 and 1852, respectively, well after his death. He also worked on creating an extensive catalog of nebulas. He also continued to work on double stars, and was the first to discover that most double stars are not mere optical doubles as had been supposed previously, but are true binary sta ...

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William Herschel, William Herschel - Biography, William Herschel - Other astronomical work, William Herschel - Discovery of infrared radiation, William Herschel - Named after Herschel

Read more here: » William Herschel: Encyclopedia II - William Herschel - Other astronomical work