Transcript How Far? - Science A 2 Z

How Far?
Measuring Distance in the Universe
How?
• Gian Domenico
Cassini, in 1672, used
a technique called
parallax to measure
the distance to Mars.
Cassini figured it out!
• The Sun is about 93
million miles from
• Earth. As Earth and Mars
never come closer than 35
million miles to each
other.
• Saturn, the most distant
planet known when
Cassini was alive, is
around 900 million miles
away.
How?
• Parallax!
What is Parallax?
• Try this out:
– Hold 1 finger out at
arm’s length
– Close one eye, and
then the other
– Notice how your finger
“jumps?
Measuring Stars
• Stars are billions of
light years away –
winking won’t help
• Our orbit is 186
million miles wide (93
million + 93 million)
– Star A and B are the
same star, as they
appear 6 months apart
How to:
• The parallax angle p is illustrated in the above
figure.
• We can determine they adjacent (d) using
trigonometry.
Trigonometry
• Our adjacent line (d in
the prior picture) is the
distance from Earth’s
Orbit (BC) to the star
(A)
• Adjacent length=
opposite length
tangent angle A
Trigonometry
• Measure the angle of the star to our central point
of orbit
Earth’s
• Simple calculation
Orbit
• Even the Hubble Telescope limited to 1000 LY
Parsec
• The method of parallax
gives rise to a natural
distance unit that
astronomers call the
parsec.
– defined as the distance at
which a star would have a
parallax angle p equal to
one second of arc.
– using trigonometry
distance equal to 206,265
astronomical units or 3.26
LY
• AU is the average
distance of Earth to Sun
Further away?
• The universe is
expanding
• Galaxies furthest away
are moving away
faster than galaxies
closer to us
• We can us Doppler
Effect
Visible Spectrum
Doppler
• Doppler
What is Red Shift?
•
•
•
•
As light moves away, the waves stretch out
Longer waves are shifted towards the red
As light moves towards us, the waves condense
Shorter waves are shifted towards the blue
Spectral Signature
• Each element has a unique spectral signature
• Two elements combine