Light Years
0 Light years is a measurement in distance, not a
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measurement of time.
Light year represents the distance that light travels in one
year.
Light from the Sun takes approximately 8 minutes (or
480seconds) to get to Earth; and 1 AU (distance Sun is to
Earth) is 149,597,871 km.
Thus
149,597,871 km = 311,662.23 km/s
480s
Lets round that and say that the speed of light is
3.0 x 105 km/s
Light Years
0 If light travels 3.0 x 105 km/s, how far does it travel in
one year?
0 (60s/m)(60m/hr)(24hr/days)(365 days/year) =
31,536,000 s/year
Thus:
3.0 x 105 km/s (31,536,000 s/year)
One Light Year = 9.5 x 1012 km/year
Measuring Distance in Space
0 The volume of the universe is 1.0 x 1030 cubic light
years. Hence, we assume the universe is 3-D and we
can measure, approximately, how big our universe is.
0 Scientists have a multitude of ways to measure
distance in space, but because we cannot just lay a
ruler down and measure distances we need to use
complex mathematical equations.
0 The three ways we will learn to measure distance in
Space is : 1) Parallax, 2) Baselines, and 3) Red Shifts.
Parallax
0 Parallax is measuring the apparent motion of a nearby
star against the background of a more distance nonmoving star.
0 We measure a parallax in parsec, 1 parsec is 3.26 light
years.
0 Use example from pg 420
Baselines
0 Scientists use a baseline to create a triangle and use
trigonometry to solve the distances things are.
The angle of Earth to
Saturn is 84 degrees. The
baseline distance from the
Sun to Earth is 3.0x108
Draw a straight line up
from the sun you will see
it creates a triangle. Solve
for the distance to Saturn.
Red Shifts
0 As discussed earlier, the farther we are from an object,
the more the light waves move from the violet to the
red part of the light spectrum.
0 Notice theline on the light spectrum shifts the further
we get from the star we are looking at:
Sample Problem #1
0 Page 423
0 Assignment – Page 424, Questions 2, 3, 16 and 17