At right is a visual image of Sirius, the brightest star as seen from Earth, apart from the Sun.
An example of the differences between visual stellar classification and a possible X-ray classification is the disparity between the image of Sirius A [at above centre in the overexposed Hubble image] with the dim Sirius B [tiny dot at lower left]. [The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.] And, the lower image of the same two stars in X-rays.
This image shows two sources and a spike-like pattern due to the support structure for the transmission grating. The bright source is Sirius B, a white dwarf star that has a surface temperature of about 25,000 degrees Celsius which produces very low energy X-rays. The dim source at the position of Sirius A – a normal star more than twice as massive as the Sun – may be due to ultraviolet radiation from Sirius A leaking through the filter on the detector. In contrast, Sirius A is the brightest star in the northern sky when viewed with an optical telescope, while Sirius B is 10,000 times dimmer.
In the bottom image, Sirius B clearly outshines Sirius A. However, in the visual range the reverse is the case as shown in the top image. The surface effective temperature of Sirius A (spectral type A1V) is only 9,940±210 K, while that of Sirius B (a white dwarf, DA2) is 25,200 K. On the surface temperature of the photosphere alone, Sirius B would be a Class B star.
A variety of elemental violet lines occur in the star Sirius. These include calcium (Ca I & II), iron (Fe I), magnesium (Mg I & II), manganese (Mn I & II), nickel (Ni II), scandium (Sc II), silicon (Si II), strontium (Sr II), titanium (Ti II), vanadium (V II), yttrium (Y II), and zirconium (Zr II).
Around 150 AD, the Hellenistic astronomer Claudius Ptolemy described Sirius as reddish, along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux, all of which are clearly of orange or red hue. The discrepancy was first noted by amateur astronomer Thomas Barker, ... who prepared a paper and spoke at a meeting of the Royal Society in London in 1760. The existence of other stars changing in brightness gave credence to the idea that some may change in colour too; Sir John Herschel noted this in 1839, possibly influenced by witnessing Eta Carinae two years earlier. Thomas Jefferson Jackson See resurrected discussion on red Sirius with the publication of several papers in 1892, and a final summary in 1926. He cited not only Ptolemy but also the poet Aratus, the orator Cicero, and general Germanicus as colouring the star red, though acknowledging that none of the latter three authors were astronomers, the last two merely translating Aratus' poem Phaenomena. Seneca, too, had described Sirius as being of a deeper red colour than Mars. However, not all ancient observers saw Sirius as red. The 1st century AD poet Marcus Manilius described it as "sea-blue", as did the 4th century Avienus. It is the standard star for the color white in ancient China, and multiple records from the 2nd century BC up to the 7th century AD all describe Sirius as white in hue.
In 1985, German astronomers Wolfhard Schlosser and Werner Bergmann published an account of an 8th century Lombardic manuscript, which contains De cursu stellarum ratio by St. Gregory of Tours. The Latin text taught readers how to determine the times of nighttime prayers from positions of the stars, and Sirius is described within as rubeola — "reddish". The authors proposed this was further evidence Sirius B had been a red giant at the time.
Although IK Tauri is far below naked eye visibility even at maximum brightness, due to the low temperature and strong extinction at visual wavelengths, in the infrared, it is brighter than prominent stars such as Rigel (K-band magnitude +0.18) and comparable to Sirius (K-band magnitude −1.35).
Both Al I absorption lines at 394.401±8.5 and 396.152±6.5 have been measured for Sirius.
The chemistry of vanadium includes four adjacent oxidation states 2-5. In aqueous solution the colours are lilac V2+(aq), green V3+(aq), blue VO2+(aq) and, at high pH, yellow VO42-.
Vanadium (V II) has an absorption band, 392.973-403.678 nm, with an excitation potential range of 1.07-1.81 eV.
Chromium has absorption lines that occur at 425.435-428.972 nm from Cr I and 400.333-428.421 nm, 3.09-6.46 eV from Cr II near Sirius.
Manganese (Mn I) has two absorption bands at 403.449±1.4 nm and 405.554±0.8 nm, where the second has an excitation potential of 2.13 eV.
Manganese (Mn II) has an absorption band at 420.638±0.8 nm with an excitation potential of 5.37 eV.
It was not until 31 January 1862 that Alvan Graham Clark observed a previously unseen star close to Sirius, later identified as the predicted companion. Walter Adams announced in 1915 that he had found the spectrum of Sirius B to be similar to that of Sirius.
In the drawing on the right, "Sinuosités observées dans le mouvement propre de Sirius."
On the left is a diagram of the proper motion of Sirius against the background stars.
For locating Sirius use a line through the three stars in Orion's belt to the left into Canis Major per the image on the right.
On the right is a spatial representation of every star within 14 light-years of Sol. There are 32 known stars in this region, including Sol. The stars are coloured according to the spectral type, which may not reflect the actual colour. Please see this Wikipedia article for the listing of stars. If a star is double or triple the stars are shown stacked vertically: the actual position is the star closest to the centre plane. The stars on this map may not all be visible to the naked eye, as many are dwarf stars. Some of this information may be preliminary and not entirely accurate as a result. The coordinate system is right ascension and declination. Hours of RA are marked, as well as distance in multiples of 5 light-years.
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