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-          A constellation is a region of the sky with well defined borders; familiar star patterns help us locate these constellations.

-          To help us understand and map the sky. For reference, we identify 4 special points:-
- The north celestial pole is the point directly over the Earth's North Pole

- The south celestial pole ''           ''          ''          ''          "            South Pole

- The celestial equator , which is a projection of Earth's equator into space,

   makes a complete circle around the celestial sphere.

- The ecliptic is the path the sun follows as it appears to circle around the

  celestial sphere once each year. (23.5 degrees; same as earth)

Local sky

-The point directly overhead (90 degrees perpendicular) is the Zenith.

- The meridian  is an imaginary line stretching between the 2 opposite sides of the horizon.

- We can pinpoint the position of any object in the local sky by stating its direction/azimuth  and its altitude  above the horizon.

-          Angular size of an object is the angle it appears to span in your field of view. The farther away an object is the smaller its angular size.

-          Angular distance between a pair of objects in the sky is the angle that appears to separate them in your field of view.

-          Latitude measure the north-south position on earth. (0 degrees at equator , 90 at north pole & affects constellations)
Longitude  measures east-west position. (is defined to be 0 degress along a line passing through Greenwich, England.

-           

-          The Seasons change every 3 months starting in summer; June

-           Lunar phases are the cycle of which the moon changes appearance and the time at which it rises.

-          Lunar eclipse occurs when Earth lies directly between the Sun and the Moon, so that the Earth's shadow falls on the moon

-          There are 3 types of lunar eclipses:-

-          1- Total lunar eclipse           
2-partial lunar eclipse

-          3- penumbral eclipse

-          Solar eclipse occurs when the moon lies in between the sun and the earth and so sun will completely or partially blocked.

1 Arseconnd:- The width of a finger at arm's length is about 1 degree. Remember that there are 60 arcminutes in 1 degree and 60 arcseconds in 1 arcminute.

Anglular size  = Physical size

        360 °             2 ¶ x distance

Ex. The angular diameter on the moon is about 0.5 degrees and the moon is about 380,000 km away. What is the Moon's physical diameter?

Solution

0.5     x          380,000
360°         2 ¶  x distance

=3316

= 3300 (rounded to nearest hundred) ¯

- The sun is highest up the sky during its equinoxes; spring and fall.