Astronomy 2022A: Origin of the Universe Measuring the Universe Pearson Educa-on
Dec 04, 2015
Astronomy 2022A: Origin of the Universe
Measuring the Universe
Pearson Educa-on
Today’s agenda:
What units are used to measure astronomical distances?
What methods are used to measure astronomical distances?
How do these compare to the everyday world?
hBp://today.io/qjpr
TwiBer: #Astro2022
There’s a reason big numbers are called “astronomical”
Earth’s diameter: – 12756 km
Earth-‐Sun: – 150 000 000 km
Earth-‐Pluto – 6 000 000 000 km
Earth-‐nearest stars – 10 000 000 000 000 km
Earth-‐centre of our Milky Way galaxy – 200 000 000 000 000 000 km
Earth-‐Andromeda Galaxy (M31) – 20 000 000 000 000 000 000 km
Earth-‐edge of observable Universe – 100 000 000 000 000 000 000 000 km
50 000 000 000 000 = 5 x 1013
We use scienXfic (aka exponenXal) notaXon to write big and small numbers
0.0000000082 = 8.2 x 10-‐9
exponent
To mulXply or divide, mulXply or divide first part, then add or subtract exponents
(5 x 1013)/ (4 x 1016 )=
(5/4) x 1013-‐16 =
1.25 x 10-‐3
The Earth-‐Sun distance is called an astronomical unit (AU); 1 AU is 150 million km
Note the scale: Jupiter is about 5 AU from Sun, Neptune 30
1 light-‐year is about 1013 km
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1 light - year = (speed of light) × (1 year)
= 300,000 kms
⎛
⎝ ⎜
⎞
⎠ ⎟ ×
365 days1 yr
×24 hr1 day
×60 min
1 hr×
60 s1 min
⎛
⎝ ⎜
⎞
⎠ ⎟
= 9,460,000,000,000 km
Pearson Educa-
on
Distances within our galaxy are measured in light-‐years Wikiped
ia, Pearson
Edu
ca-o
n
• Know speed of light
• Measure travel Xme
• Compute distance
Distances within the solar system can be measured using light travel Xme
We measure distances within the Milky Way using parallax
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on
Brightness alone does not provide enough informaXon to measure distances in astronomy
Luminosity Brightness = 4π (distance)2
Cepheid variable stars vary in luminosity over a Xme proporXonal to their average luminosity
Astronomyinyourhands.com, Pearson Educa-on, STScI
Other techniques are used to measure distances to galaxies further away
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The “Cosmic Calendar’’ compresses the history of the universe into 1 year
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Timescales in cosmology are (millions or billions) of years
Ordero>ime.com hBp://en.wikipedia.org/wiki/Graphical_Xmeline_of_the_universe
3 x 1010
3 x 105
3 x 100
NB: Logarithmic scale!
End of class.
For next week: please read State of the Universe, Chapter 3