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Astronomy (177)
AST201H5 (68)
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Lecture

# summary_ch2.pdf

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School
University of Toronto Mississauga
Department
Astronomy
Course
AST201H5
Professor
J B Lester
Semester
Fall

Description
AST 201S - Stars and Galaxies University of Toronto Mississauga Chapter 2 Summary Essential Cosmic Evolution, 5 Edition th 1. “Size” of an astronomical object is the angle made by the rays of light from its opposite sides converging at our eye. • If the object is round, like the Sun, we refer to its angular diameter • If the object is irregular in shape, it will have an angular width and angular height • The term “angular size” covers both cases • Two separate objects have an “angular separation” on the sky 2. Angles have units • Degrees - indicated by . There are 360 in a full circle. Most astronomical ◦ ◦ objects are less than 1 . For example, the Sun’s angular diameter is 0.5 . 1 ′ • Minute of arc = 60, written 1 - still larger than most astronomical objects 1′ 1◦ ′′ • Second of arc = 60 = 3600 written 1 - a common astronomical size • NOTE: always add “of arc” to distinguish angles from time 3. Angular size depends on two properties of the object observed • the actual diameter or size (in km) of the object = D • the distance (in km) of the object from Earth = d actual size D In terms of these, angular size ∝ = d
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