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Astronomy (238)
AS101 (238)
Lecture

# September 20.docx

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Department
Astronomy
Course
AS101
Professor
Shohini Ghose
Semester
Fall

Description
September 20, 2011  100 billion stars in our galaxy  100 billion galaxies  The size of the observable universe is roughly 130,000,000,000,000,000,000,000 km  Some commonly used distance units: o 1ly (light year) is the distance light travels in 1 year o Speed of light = 300,000 km/s o In 1 second sight travels 300,000km o The astronomical unit (au) o The earth’s orbit around the sun is elliptical. Hence the distance between the earth and sun varies at different points o 1 au = Average distance between earth and sun  What is the size of the earth in astronomical units? 150,000,000 km = 1 au 130,000,000,000,000,000,000,000 km = (1au/150,000,000 km) x 130,000,000,000,000,000,000,000 km =8,666,666,666,667 au =Roughly 8.67 trillion au (NOW. The universe is always expanding)  What is the size of the earth in light years? 9,460,000,000,000 km = 1 ly 130,000,000,000,000,000,000,000 km = (1ly/ 9460,000,000,000km) x 130,000,000,000,000,000,000,000 km = 13,742,071,882 ly = roughly 14 billion ly  Scientific Notation: every number can be expressed as a mul
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