Astronomy

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The Altitude Azimuth coordinate system Observer
in Aurora latitude 42º 30 45N
longitude 76º 41 30 W
Altitude angle up from horizon between 0º and
90º
Zenith
Azimuth angle E of N from North direction on
horizon between 0º and 360º
Horizon
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The Celestial Sphere as seen by an Inuit (living
near the NP)
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Its Time for Facts about Time

• Earth rotates steadily, once in 24 h (15º in 1 h)
• direction is West to East looking down onto
  NP, its counterclockwise (ccw)
• no matter where you are, local noon is the
  moment
• exactly halfway between sunrise and sunset
• when the sun is at its highest point in the sky
• the sun is due south and therefore is crossing
  the meridian
• Time zones are a compromise such that the zone
  center, a clock reads 1200 at local noon
• West of center, local noon occurs up to 30 min
  after 1200 East of center

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Lets go to the board and talk about degrees and
radians and all that s, q and r language
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A relationship between sizes

• D object size ( arc length s) in some units
• d distance from eye to object ( radius r) in
  same units
• so subtended angle q angle in radians D/d

To convert q to seconds of angle

• Since p rad 180º and 1º 60 and 1 60
• We have q (D/d)(180º/p)(60/º)(60/)
• So, doing the multiplication we get
• q 206,265(D/d)
• where q is in seconds of arc, and D d must be
  in the same length units

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Insert numbers for a penny d 4 km 4 x 103
m D 2 cm 2 x 10-2 m So q 206,265(D/d)
1.03 x 100 '' 1 ''
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Fig.01.11
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Careful the stars DO NOT MOVE on the celestial
sphere, but the CS rotates once per day We can
see only exactly half of the CS at any moment
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Daily (diurnal) solar motion

• in one day, the sun barely moves on the celestial
  sphere it just rides along with it.
• path is never a great circle across the sky
  except
• at vernal equinox and autumnal equinox
• rises due E, sets due W, is at 90º - latitude at
  noon
• day is exactly 12 h long everywhere on Earth
• in summer, in northern hemisphere
• Rises north of east (azimuth 90º - latitude)
  and sets north of west (azimuth 270º
  latitude)
• Day is longer than 12 h
• Sufficiently far north, sufficiently near summer
  solstice, SUN NEVER SETS!!

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Looking ahead the Declination-Right Ascension
coordinate system for an observer in North
Canada latitude 75º