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Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs. [3] The word parsec is a shortened form of a distance corresponding to a parallax of one second, coined by the British astronomer Herbert Hall Turner in 1913. [4]
Parsecs are used in astronomy to measure interstellar distances. A parsec is approximately 3.26 light-years or about 3.086×10 16 m (1.917×10 13 mi ). Combining it with the " atto- " prefix (×10 −18 ) yields attoparsec (apc), a conveniently human-scaled unit of about 3.086 centimetres (1.215 in) that is used only humorously.
[12] [13] Development of unit definition ... ≈ 4.848 136 811 13 × 10 −6 parsecs: ... because they are either too short or far too long. Distances normally change ...
As a parsec (parallax-second) is defined by the distance of an object that would appear to move exactly one second of arc against background objects, stars less than 5 parsecs away will have measured parallaxes of over 0.2 arcseconds, or 200 milliarcseconds.
Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs. [12] The word parsec is a shortened form of a distance corresponding to a parallax of one second, coined by the British astronomer Herbert Hall Turner in 1913. [13]
The apparent magnitude, the magnitude as seen by the observer (an instrument called a bolometer is used), can be measured and used with the absolute magnitude to calculate the distance d to the object in parsecs [14] as follows: = + or = (+) / where m is the apparent magnitude, and M the absolute magnitude. For this to be accurate, both ...
A Texas man was sentenced to 35 years in prison after kidnapping a 13-year-old, driving her to California, threatening her with a firearm and sexually assaulting her.
The cluster's core radius is estimated at 3.5 parsecs (11.4 light years); its half-mass radius is about 3.9 parsecs (12.7 light years); and its tidal radius is about 12 parsecs (39 light years). [7] [11] However, the tidal radius also includes many stars that are merely "passing through" and not bona fide cluster members.