Admin. 1/11/11
1.
Class website
http://www.astro.ufl.edu/~jt/teaching/ast1002/index.html
2.
Optional Discussion sections (start Jan. 18th) (see me at
end of lecture if you can’t make one of these times)
Tuesday 1.55pm (period 7), Bryant 3
Wednesday 10.40am (period 4), Bryant 3
Thursday 3.00pm (period 8), Bryant 3
Office hr: Thursday (5pm), Bryant 302
3.
Info on Quiz 1 and Homework 1 will be announced in
lecture
4.
Reading for this week: pages 134 of Chaisson &
McMillan, then continue reading from p34 onwards >
Chapter 2 (to p54).
Key Concepts: Lecture 2
Scientific Notation, Scale of the Solar System & Universe: use of
scale factors, Light travel time
Wave model of light and the electromagnetic spectrum
Daily Motion of the Sun and Stars
The Celestial Sphere
Can we imagine the scale?
SCIENTIFIC NOTATION:
The Solar System  our nearest planetary neighborhood
–Size of Earth: Radius, r = 6,400 km = 6.4 x 10 x10 x10 = 6.4x10
3
km
–Distance to Moon = 384,000km = 3.84x10
5
km
Circumference,
C = 2
!
r
= 40,000km = 4.0x10
4
km
How much bigger is the
Sun than the Earth?
7x10
5
km
6.4x10
3
km
= (7/6.4)x10
(53)
= (7/6.4)x10
2
~100
–Distance to Sun = 150x10
6
km
= 1 Astronomical Unit (AU)
–Distance from Sun to Pluto = 39.5AU = 5.9x10
9
km
–Size of Sun: Radius, r = 700,000km = 7 x 10
5
km
Can we imagine the scale?
Light travel time:
Speed of light (in vacuum), c = 300,000 km/s = 3x10
5
km/s
Distance = speed x time,
i.e.
d = c t
,
so
d / c
=
t
Work out how long light takes to cross the above distances.
Light travel time is proportional to distance:
t = (1/c) x d
t
"
d
The Sun is 1 AU away, i.e. 8.3 light minutes away.
Pluto is 39.5x8.3 light minutes = 5.5 light hours away from the Sun.
We are always looking back in time: this is a fundamental concept.
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 Spring '07
 Dr.HaywoodSmith,Jr
 Light, Wavelength, Electromagnetic spectrum, light travel time

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