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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.
June
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•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
1 AUSun E
draw this
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