AST101 (lecture2).docx

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University of Toronto St. George
Astronomy & Astrophysics
Michael Reid

AST101 (Lecture 2) What does the term “universe” mean?  The totality of all space, time, energy, and matter However big you imagine the universe to be, you are wrong It’s much, much bigger than that. Which of the following is the largest? A. Jupiter B. The Earth C. The Sun  D. The Moon E. Mercury In pictures, the distances of the planets are not to scale The solar system is HUGE and the vast majority of it is empty *tiny tiny quantity of d0ust and gas From the Sun: AU(Astronomical Unit) Mercury= 0.4AU Venus= 0.7AU Earth= 1AU =~1.5 x10^11m Mars= 1.5AU Jupiter= 5AU Neptune= 30AU A “light year” is a measure of distance Sun to the nearest star 41,746,980,000,000,000m  1”unit star unit”?!  4.4 light years  If a light year is a unit of distance so must be a light minute. Roughly how many light minutes do you think equal 1AU?  8 light minutes= 1AU If the distance between the Sun and the center of the Galaxy (Black Hole) is 26,000 light years, this means that:  It would take light 26,000 years to get from the center of the galaxy to us The Andromeda is 2.5 million ly away. It’s the nearest large galaxy in the milky way Let’s say a certain kind of star lives for 1 million year. You see such a star about 10 million ly away. What do you know for sure about the star?  It died millions of years before its light reached us.  Light travels at a finite speed. So, no matter where you look, you are looking back in time. When Mae Jamison :  Sees the sun 1 AU away
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