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Astronomy

Earth's motion around the Sun, not as simple as I thought

Azimuth​

The direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects the horizon

Asterism​

In observational astronomy, anasterismis a popularly-known stationary pattern or group of stars that are recognised in the night sky as viewed from Earth. This colloquial definitionmakes it appear quite similar to a constellation, but they differ mostly in that a constellation is an officially recognized area of the sky, while an asterism is a visually obvious collection of stars and the lines used to mentally connect them; as such, asterisms do not have officially determined boundaries and are therefore a more general concept which may refer to any identified pattern of stars. This distinction between terms remains somewhat inconsistent, varying among published sources. An asterism may be understood as an informal group of stars within the area of an official or defunct former constellation.Some include stars from more than one constellation.

List​

  • The Great Diamond consisting of Arcturus, Spica, Denebola, and Cor Caroli.An East-West line from Arcturus to Denebola forms an equilateral triangle with Cor Caroli to the North, and another with Spica to the South. The Arcturus, Regulus, Spica triangle is sometimes given the name Spring Triangle.Together these two triangles form the Diamond. Formally, the stars of the Diamond are in the constellations Boötes, Virgo, Leo, and Canes Venatici.
  • The Summer Triangle of Deneb, Altair, and Vega - The Cygni, The Aquilae, and The Lyrae - is easily recognized in the northern hemisphere summer skies, as its three stars are all of the 1st magnitude.The stars of the Triangle are in the band of the Milky Way which marks the galactic equator, and are in the direction of the galactic center.
  • TheGreat Square of Pegasus is the quadrilateral formed by the stars Markab, Scheat, Algenib, and Alpheratz, representing the body of the winged horse.The asterism was recognized as the constellationASH.IKU"The Field" on the MUL.APINcuneiform tablets from about 1100 to 700 BC.
  • One-third of the 1st-magnitude stars visible in the sky (seven of twenty-one) are in the so-called Winter Hexagon with Capella, Aldebaran, Rigel, Sirius, Procyon, and Pollux with 2nd-magnitude Castor, on the periphery, and Betelgeuse off-center.Although somewhat flattened, and thus more elliptical than circular, the figure is so large that it cannot be taken in all at once, thus making the lack of true circularity less noticeable. (The projection in the chart exaggerates the stretching.) Some prefer to regard it as aHeavenly 'G'.
  • The Winter Triangle visible in the northern sky's winter and comprise the first magnitude stars Procyon, Betelgeuse and Sirius.

Constellation based asterism​

  • A familiar asterism is the**Big Dipper, PloughorCharles's Wain,** which is composed of the seven brightest stars in Ursa Major.These stars delineate the Bear's hindquarters and exaggerated tail, or alternatively, the "handle" forming the upper outline of the bear's head and neck. With its longer tail, Ursa Minor hardly appears bearlike at all, and is widely known by its pseudonym, theLittle Dipper.
  • The Northern Cross in Cygnus.The upright runs from Deneb(α Cyg) in the Swan's tail to Albireo(β Cyg) in the beak. The transverse runs from Aljanah(ε Cyg) in one wing to Fawaris(δ Cyg) in the other.
  • TheFish Hook is the traditional Hawaiian name for Scorpius. The image will be even more obvious if the chart's lines from Antares(α Sco) to Graffias(β Sco) and Fang(π Sco) are replaced with a line from Graffias through Dschubba(δ Sco) to Pi forming a large capped "J."
  • TheSouthern Cross is an asterism by name, but the whole area is now recognised as the constellation Crux. The main stars are Acrux, Mimosa, Gacrux, Imai, and arguably also, Ginan. Earlier, Cruxwasdeemed an asterism when Bayer created it in Uranometria(1603) from the stars in the hind legs of Centaurus, decreasing the size of Centaur. These same stars were probably identified by Pliny the Elder in his Naturalis Historia as the asterism 'Thronos Caesaris.'
  • Adding vertical lines to connect the limbs at the left and right in the main diagram of Hercules will complete the figure of theButterfly.
  • Although hardly an ancient notion, it is easy to see why theIce Cream Coneis sometimes applied to Boötes. It is even better known as theKite.
  • The stars of Cassiopeia form a W which is often used as a nickname.

Some asterisms may also be part of a constellation referring to the traditional figuring of the whole outline. For example, there are:

Orian's Belt / Belt of Orion​

The names of the three stars come from Arabic;Alnilam(النظام) means "string of pearls" or is related to the wordnilam("sapphire") with the spellingsAlnihanandAlnitam, Mintaka means belt.

Alnitak​

Alnitak (ζ Orionis) is a triple star system at the eastern end of Orion's belt and is 1,260 light-years from the Earth. Alnitak B is a 4th-magnitude B-type star which orbits Alnitak A every 1,500 years. The primary (Alnitak A) is itself a close binary, comprising Alnitak Aa (a blue supergiant of spectral type O9.7 Ibe and an apparent magnitude of 2.0) and Alnitak Ab (a blue dwarf of spectral type O9V and an apparent magnitude of about 4). Alnitak Aa is estimated as being up to 28 times as massive as the Sun, and to have a diameter 20 times greater. It is the brightest star of class O in the night sky.

Alnilam​

Alnilam (ε Orionis) is a supergiant, approximately 1,340 light-years away from Earth and magnitude 1.70. It is the 29th-brightest star in the sky and the fourth-brightest in Orion. It is 375,000 times more luminous than the Sun.Its spectrum serves as one of the stable anchor points by which other stars are classified.

Mintaka​

Mintaka (δ Orionis) is 1,200 light-years away and shines with magnitude 2.21. Mintaka is 90,000 times more luminous than the Sun. Mintaka is a double star. The two stars orbit around each other every 5.73 days.

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Space / Aerospace Engineering​

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Chandrayaan-3

Others​

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