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Distances in Space
Science 9
Using scientific notation
• Distances in space are very large
• We use scientific notation to represent very large
and very small numbers
• The first digit is between 1 and 9
• This is called the base
• Followed by a power of 10
• The exponent indicates how far to move the
decimal point
• Ex. 2 000 000 000 people = 2 x 109 people
How Astronomers Measure Distances
• Triangulation is how astronomers measure
distances to objects in the solar system and
beyond
• A baseline gives us a starting point which is used
for comparisons
• The diameter of Earth is often used by
astronomers, which is 1.3 x 104 km
▫ This value can then be used to calculate the
distance to stars
Distances to the Stars
• The distance from our Sun to the next nearest
star is 4.1 x 1013 km
• Because these numbers get so large,
astronomers have come up with another way to
measure distance, the light year
▫ The distance that light travels in one year is equal
to one light year
▫ Light travels at a speed of 3 x 105km in 1 second
▫ In one year, it travels 9.46 x 1012 km
Some Distances of Objects from Earth
• The light we see from the star Alpha Centauri
took 4.3 years ago
• The most distant known galaxy from Earth is
15 000 000 000 light years from us
• Measurements in light years not only tell us how
far away something is from us but how much
time has passed since the light left that object
Practice with Scientific Notation
1. Write the following numbers in scientific
notation.
a. 1 000 000 000m
b. 246 000 000 000 000 000 km
c. 0.000 000 8mm
d. 450 m
e. 0.000 000 000 000 000 12cm
f. 333 000 000 000 000 000 000 000 000 km
For the remainder of class:
Questions 2, 4, 5 on page 445
Questions 1, 3, 4, 6 on page 439