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Stars that have magnitudes between 1.5 and 2.5 are called second-magnitude; there are some 20 stars brighter than 1.5, which are first-magnitude stars (see the list of brightest stars). For example, Sirius is magnitude −1.46, Arcturus is −0.04, Aldebaran is 0.85, Spica is 1.04, and Procyon is 0.34. Under the ancient magnitude system, all of ...
She also used types such as B5A for stars halfway between types B and A, F2G for stars one fifth of the way from F to G, and so on. [60] [61] Finally, by 1912, Cannon had changed the types B, A, B5A, F2G, etc. to B0, A0, B5, F2, etc. [62] [63] This is essentially the modern form of the Harvard classification system. This system was developed ...
+6.5: Approximate limit of stars observed by a mean naked eye observer under very good conditions. There are about 9,500 stars visible to mag 6.5. [5] +6.64: dwarf planet Ceres: seen from Earth maximum brightness +6.75: asteroid Iris: seen from Earth maximum brightness +6.90: spiral galaxy M81: seen from Earth
The planets seem to move forward and back, changing their position over short periods of time (weeks or months). They always seem to move within the band of stars called the zodiac by Westerners. The planets can also be distinguished from fixed stars because stars tend to twinkle, while planets appear to shine with a steady light.
In astronomy, the rotation period or spin period [1] of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars (inertial space).
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
within 5° used to be the North Star at about 4,420 BC Alpha Draconis: Thuban: 3.65: Draco: within 0.1° used to be the North Star at about 3,000 BC Kappa Draconis: 3.82: Draco: within 6° a near-north star, shares timing with Kochab: Beta Ursae Minoris: Kochab: 2.08: Ursa Minor: within 7° used to be the North Star at about 1,100 BC
Some stars visible to the naked eye have such a low absolute magnitude that they would appear bright enough to outshine the planets and cast shadows if they were at 10 parsecs from the Earth. Examples include Rigel (−7.8), Deneb (−8.4), Naos (−6.2), and Betelgeuse (−5.8).