Transcript parallax and triangulation

Distances in Space
How Far Away are Stars & Other
Celestial Bodies?
• Use Stellarium to observe the sky and
discuss what observations you might be
able to use to determine which objects
are closest to Earth.
• Do size and brightness always lead to
accurate conclusions about the
distances between Earth and objects
out in space?
Distances in Space
• Objects in space are so far apart that
it doesn’t make sense to use units of
measurement like kilometers.
• Instead, we use astonomical units
(AU’s) or light years to describe these
huge distances.
Astronomical Unit
• used for measuring “local distances” …
those INSIDE our solar system
• 1 AU = average distance from the
center of Earth to center of the Sun
(149 599 000 km)
Science In Action p. 379
Light Year = ~10 trillion km
• used for measuring distances outside our solar
system
• IT DOES NOT MEASURE TIME – it is the distance
light can travel in a year
• light travels about 300,000 kilometers per second.
• there are 60 seconds in a minute, 60 minutes in an
hour, 24 hours in a day, and about 365.25 days in a
year.
• if we multiply all those numbers together, we come
up with approximately 10 trillion kilometers as the
distance light can travel in one year.
Views of the Past
• because it takes time for light from an
object to travel to Earth what we see is
images from the past
– light from the Moon is 1.3 seconds old
– light from the Sun is ~8 minutes old
– light from Pluto is 5 hours old
– light from a star in the centre of our
galaxy is
25 000 years old
– using the Hubble Space Telescope we can
see images that have taken 12 billion years
to reach Earth
(…the Earth is about 4.6 billion years old!)
Parallax
• How do we know the distance to various
stars and planets?
– In 1672, Giovanni Cassini used parallax to
determine the distance from Earth to the
Sun
• What is parallax?
– Hold a finger up about three to five inches
in front of your nose, focus on a distant
object, and then alternately open and close
each eye.
– What happens?
With parallax… if you look at the same star from
two different location on Earth at the same
time, nearby stars will appear to shift in position
relative to other, more distant stars.
Distant
Star A
Closer
Star
Distant
Star B
OR you can look at the same star from the same
place on Earth… but at 2 different times of
the year
Science In Action p.450
Triangulation
• How can parallax be used to measure
distances in space?
It involves
triangulation which
involves the
mathematics of
triangles, angles and
trigonometry
• 1st - we need to use our knowledge of
parallax… take a measurement of an object in
space from 2 points on Earth (or from the
same point at 2 different times)
• that gives us 2 angles for our triangle
• 2nd - we need to measure the base of our
triangle
• 3rd – we need to understand trigonometry
…sometime after grade 9! 
Instead of using trigonometry…
we will create a scale diagram to
figure out the distance to an
object!
Let’s try it out…