today - harvey mudd college · 2010. 1. 5. · astronomy 101 lecture #1 ecliptic to equatorial...
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Astronomy 101 Lecture #1
Today: Introduction Coordinate Systems Transformations Astrometry
Reading: Ch. 1, 4
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Astronomy 101 Lecture #1
Altitude – Azimuth Coordinate System
alt (a) = altitude
az (A) = azimuth
z = 90o – a = zenith distance
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Astronomy 101 Lecture #1
Equatorial Coordinate
System
Declination DEC or δ
Right Ascension RA or α
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Astronomy 101 Lecture #1
Ecliptic in Equatorial Coordinates
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Astronomy 101 Lecture #1
Does Sun move in the direction of increasing or decreasing RA?
Increasing RA
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Astronomy 101 Lecture #1
Galactic Coordinate System
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Astronomy 101 Lecture #1
Galactic Coordinate System
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Hour Angle (HA) is measured westward from the observer's Meridian. It is analogous to RA. HA = 0 on the meridianHA < 0 E of meridianHA > 0 W of meridian
Astronomy 101 Lecture #1
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Astronomy 101 Lecture #1
Horizon to Equatorial Coordinate
Transformation
Equivalent to a rotation by angle (90o – .
= latitude of observer
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Astronomy 101 Lecture #1
Ecliptic to Equatorial Coordinate Transformation
1. (alt, az) to (HA, DEC)
2. (HA, DEC) to (alt, az)
cosDEC⋅sinHA=cos alt⋅sin az
cosDEC⋅cosHA=cos⋅sin altsin⋅cos alt⋅cosazsinDEC=sin⋅sin altcos⋅cos alt⋅cosaz
cosalt⋅cos az=−cos⋅sinDECsin⋅cosDEC⋅cosHAsin alt=sin⋅sinDECcos⋅cosDEC⋅cosHA
cosDEC⋅cosHA=cos⋅sin altsin⋅cos alt⋅cosazsinDEC=sin⋅sin altcos⋅cos alt⋅cosaz
cosDEC⋅cosHA=cos⋅sin altsin⋅cos alt⋅cosazsinDEC=sin⋅sin altcos⋅cos alt⋅cosaz
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Astronomy 101 Lecture #1
Galactic to Equatorial Coordinate Transformation
1. (l, b) to (RA, DEC)
2. (RA, DEC) to (l, b)
cos b⋅cos l−33o =cosDEC⋅cos RA−282.25o
cosDEC⋅sin RA−282.25o=cosb⋅sin l−33o⋅cos 62.6o−sin b⋅sin 62.6o
sinDEC=cos b⋅sin l−33o⋅sin62.6osin b⋅cos 62.6o
cos b sin l−33o=cosDEC⋅sin RA−282.5o⋅cos 62.6osinDEC⋅sin 62.6o
sin b=sinDEC⋅cos 62.6o−cosDEC⋅sin RA−282.5o⋅sin62.6o
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Hipparcos Space Astrometry Mission Launch: August 1989Terminated: August 1993
Hipparcos Catalog (1996): 120,000 stars 1 milliarcsec
Tycho Catalog (1996): 1 million stars 2030 milliarcsec 2 colors
Tycho2 Catalog (2000): 2.5 million stars 2 colors
Astronomy 101 Lecture #1
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Sun
N
Period = 25,750 years
Astronomy 101 Lecture #1
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Correcting for Precession
(0, 0) are coordinates at some epoch E (, ) are coordinates at epoch E0 +T T is measured in years = 50.29'' yr1 is the precession rate = 23o27'8'' is the obliquity of the ecliptic
=0T cossin sin0 tan 0
= 0T sin cos 0
Astronomy 101 Lecture #1
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Astronomy 101 Lecture #1
Atmospheric Refraction
Shift is less than 1” if z<60o