Transcript Measuring the Earth - Bethpage Union Free School District

Do Now:
1) What are the 3 spheres of Earth?
2) Which layer is most dense?
3) We are known as the _____ planet
because we are covered by 71% of
water.
Measuring the Earth
Aim: Is Earth really a perfect
sphere?
How do we know that Earth is
spherical?

1. Satellite
images –
we can now
take photos of
Earth from
space, seeing
its true shape.
Picture from the Apollo Mission
Cont’d
2. Sailing Ships - Watching
ships “disappear” over the
horizon

Cont’d

3. Lunar Eclipse
• Earth casts a slightly rounded shadow on
the Moon

4. Polaris – (the North Star)
• As you move along the same line of latitude,
Polaris’ altitude stays the same, but as you
move along a line of longitude, Polaris’
altitude changes
*Polaris’ altitude = your Northern
latitude
Polaris
Ursa Major and Ursa Minor
Finding Locations Using Polaris


Sextant - instrument for measuring the
altitude of the sun or another celestial
body
• Parts Includes:
 Telescope - locating the North Star
 Protractor - finding the altitude (=
latitude)
Measurements can then be used to
determine the observer's geographical
position
Sextant
Is Earth a PERFECT
sphere?
What shape is the Earth?


Earth is considered to be an
Oblate Spheroid.
This means that Earth is
slightly flattened at the poles
and slightly bulging at the
equator.
• Because of the rotation – matter
“bunches” in the middle
How big is Earth?




Polar Diameter =
12,714 km
Equatorial Diameter =
12,756 km
The Earth is only slightly oblate, so
it appears to be spherical!
How does this affect gravity?

5. Gravity Measures –
the closer to Earth’s core (center), the
more gravitational pull, the more an
object weighs.
Weight and Gravity
• Equator - the Earth's
diameter is greatest;
objects weigh a little less.
• Poles - the Earth's
diameter is the least,
objects weight a little
more.
Closure Questions:
1)
The Earth’s shape most closely
resembles which of the following
objects?
(a) a football
(b) a pear
(c) a ping-pong ball
(d) an apple
2) The true shape of the Earth is best
described as a:
(a) perfect sphere
(b) slightly oblate sphere
(c) perfect ellipse
(d) highly eccentric ellipse
3) An observer watching a sailing ship
notes that it appears to be “sinking” as it
moves away. This observation proved
that:
(a) the surface of the ocean has
depressions
(b) the earth is rotating
(c) the earth is revolving
(d) the earth has a curved surface