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The Quadrantids (QUA) are a meteor shower that peaks in early January and whose radiant lies in the constellation Boötes.The zenithal hourly rate (ZHR) of this shower can be as high as that of two other reliably rich meteor showers, the Perseids in August and the Geminids in December, [4] yet Quadrantid meteors are not seen as often as those of the two other showers because the time frame of ...
The December Phi Cassiopeiids are a recently discovered early December meteor shower that radiates from Cassiopeia. Phi Cassiopeiids are very slow, with an entry velocity of approximately 16.7 kilometers per second. The shower's parent body is a Jupiter family comet, though its specific identity is unknown. [45]
Sine quadrant: A type of quadrant used by medieval Arabic astronomers, it was described by Muhammad ibn Mūsā al-Khwārizmī in 9th century Baghdad. [44] Scimitar: The curved sword or "scimitar" was widespread throughout the Middle East from at least the Ottoman period, with early examples dating to Abbasid era (9th century) Khurasan. [45]
Therefore, as the ray reflects first from side x then side y and finally from side z the ray direction goes from [a, b, c] to [−a, b, c] to [−a, −b, c] to [−a, −b, −c] and it leaves the corner with all three components of its direction exactly reversed. Corner reflectors occur in two varieties.
The galaxy's prodigious star formation began five million years ago, in a region with a diameter of 1,000 light-years. The core's structure is also unique because the galaxy has spiral arms which feed gas into the bar. [83] NGC 4414 is an unbarred spiral flocculent galaxy about 62 million light-years away. It is one of the closest flocculent ...
Several types of astrophysical objects emit X-rays, from galaxy clusters, through black holes in active galactic nuclei to galactic objects such as supernova remnants, stars, and binary stars containing a white dwarf (cataclysmic variable stars), neutron star or black hole (X-ray binaries).