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AST101H5 Lecture Notes - Angular Diameter, New Moon, Solar Eclipse Of April 8, 2024

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John Lester

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Chapter 2 - Discovering the Sky (Sept. 12)
Lecture Notes
- Stars in a constellation may not be close to each other in space - just appear grouped
from Earth (star charts on p A-28 to 31 in Appendix 1)
- Constellations serve as a background used to detect the motions of solar system
Local Sky
- Our location on Earth determines our horizon, zenith and meridian
- Degrees - 360 full circle
- Minute of arc - 1’ = 1 degree / 60
- Second of arc - 1” = 1’ / 60 = 1 degree / 3600
Angles and Distance
- We see the angle of an object
- That angle depends on its distance from us
Cosmic Calculation with Angles
angular size / 360 degrees = diameter / circumference=2pi x distance
- We measure angular size and distance, solve for diameter
diameter = angular size x 2pi x distance / 360 degrees
Apparent Rising and Setting
- Earth’s counterclockwise rotation causes all astronomical objects to appear to rise/set
every day
Sept. 14
Sun’s Rising/Setting - Solar Time
- The meridian tracks the sun (meridian being at the highest point of the sun)
- Sun arrives on the meridian line at noon and midnight
- Spinning and orbiting around the sun
- Star (Sidereal) Time - same idea based on meridian
- Spinning, NOT orbiting around the star(s)
Seasons and Calendars
- A common misconception - seasons are caused by Earth being closer to or farther
from the Sun - WRONG
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