Download Astronomical Distances

Astronomical
Distances
Stars that seem to be close may
actually be very far away from each
other.
• The universe is immense in size
• Astronomers use units and
methods of measuring that we are
not used to on Earth
• Parallax is used to measure the
distance to nearby stars
• Parallax: when objects appear to
move or shift due to earth’s orbit
★This method uses trigonometry
★nearby stars = 300 light years or
less
Parallax
Jan.
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June
•Inverse square law of light is used
for distant stars
•the intensity of light falls off as the
square of the distance from the
source
• Light year is a unit of distance,
NOT time
• Light Year: the distance light
travels in one year (9.5 trillion
km!!!)
★Kilometers are too small to use in
astronomy
★one light-year is equal to
9,500,000,000,000 kilometers.
Light Year
• Parsec is used to measure greater
distances between stars and
galaxies
• 1 parsec = 3.26 light years
• Astronomical Units (AUs) measure
distances between planets (our
solar system)
• AU is the average distance
between the Earth and Sun (1 AU)
★1 AU is about 150 million km
★Mercury is the closest at 0.39 AUs while
Neptune is the farthest at 30.06 AUs
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1 AU
Sun
E
60 second summary
Review#1 What is
parallax used for?
• to measure a star’s temperature
• to measure a star’s distance from
Earth
• to measure a star’s mass
• to measure a star’s magnitude
๏parallax measures a star’s distance
from earth
Review#2 What does
a light year measure?
• temperature
• time
• distance
• magnitude
๏distance
Reviw#3 An AU is
used for distances
between...
• stars
• galaxies
• solar systems
• planets
๏planets
Review#4 Which
measurement is used
for distant stars?
• AU
• parallax
• inverse square law of light
• light year
๏inverse square law of light