# UMD ASTR 120 - Class 9 Celestial coordinates and navigation (12 pages)

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## Class 9 Celestial coordinates and navigation

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## Class 9 Celestial coordinates and navigation

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Lecture Notes

Pages:
12
School:
University of Maryland, College Park
Course:
Astr 120 - Introductory Astrophysics - Solar System
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Unformatted text preview:

Class 9 Celestial coordinates and navigation Celestial coordinates Basic principles of navigation The longitude problem 1 I Celestial coordinates Astronomers need to be able to describe the position of an object in the sky need a coordinate system for the sky Most common choice is the RA Dec system the celestial version of latitude and longitude Declination Angle from the celestial equator to the object measured in degrees Right Ascension RA Consider a line running from the north to south celestial poles through the vernal equinox The RA is the angular distance from this line to the object typically measured in terms of hours 2 Examples Jupiter today RA 18h 58m 2s Dec 23o 5 8 Center of Andromeda galaxy RA 00h 42m 44s Dec 41o 16 09 3 Why do all objects change their RA and Dec over time 4 Another common choice Galactic Latitude and Longitude II Basics of navigation Astronomy and navigation have close ties Imagine you are on a ship in the middle of the ocean without GPS how do you figure out where you are A good topic for discussion 5 6 Google The Longitude Problem 1675 Royal Observatory at Greenwich established by Charles II in order to solve the problem of finding longitude at sea 1714 British Government established the Longitude Prize 20 000 pounds 7 million dollars today Winner must devise method for finding longitude to within half a degree during a journey from Britain to New World Board of prominent scientists established to oversea prize 7 John Harrison 8 H1 H2 H3 9 H4 H5 10 11 12

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