Download But how to find Polaris?

• No matter what kind of
map is made, some
portion of the Earth’s
surface will always look
either too small, too big,
or out of place.
Mapmakers have,
however, found ways to
limit the distortion of
shape, size, distance and
direction.
How do we know the Earth is not flat?
• EVIDENCE FOR EARTH’S SPHERICAL
SHAPE
– Ships appear to “sink” as they approach the horizon
– Other celestial objects are round.
– Now we can see earth from space, and photograph it!
• BUT, the most important proof that Earth is round is the
fact that the altitude of Polaris increases as you move
toward the North pole, or decreases as you move toward
the equator!
– This would not happen on a flat Earth. A quicker way to say it is
“the altitude of Polaris changes directly with latitude.”
• This is a more realistic
view of Earth
• It’s not really as
“oblate” or oval
• But it’s still an oblate
sphere – can you tell
by looking at the
dimensions?
Rough or Smooth?
• This picture from
space makes Earth
look very smooth.
• This picture of the
Grand Canyon makes
the Earth look rough
• Which is the case?
Rough Vs. Smooth: Its all relative!
• When standing on Earth looking at the Grand
Canyon the Earth’s surface looks very rough.
– This is because you are comparing the surface with
yourself as a frame of reference (a scale to compare
size)
• When seen from space, the Earth looks very
smooth.
– This is because you are comparing the mountains and
valleys with the entire planet for scale!
MEASURING EARTH
• How would you measure the circumference of
Earth?
• Could you determine it using no technology?
• It’s not a very simple problem.
• A Greek scientist named Eratosthenes used a
simple solution to determine earth's circumference
– 2,200 years ago!
• A proportion is making the
Proportions!
mathematical statement that
two ratios are equal
• Eratosthenes knew if he
could figure out any portion
of the 360 circumference of
the Earth he could solve for
the whole circumference!
• Remarkably, Eratosthenes
determined the
•What was his percent error? circumference to be 25,000
miles, just 99 miles over the
actual circumference at the
%D = . 396%!
equator (24,901 miles).
Where are we?
• How would you keep track of where you are
on such a big planet? At first, people used
stars…
USING STARS TO NAVIGATE
• Early sailors used a
device like this to know
where they were on this
huge Earth.
• The device was used to
measure the angle
between a star, and the
horizon. This angle is the
altitude of the star.
The Altitude of Polaris
• By far the most important star was Polaris,
or the North star, because the altitude of
Polaris told you how far North of the
equator you were (latitude!)
• Remember as distance increases the altitude
decreases or angular distance from the
horizon!
• But how to find Polaris?
– Contrary to popular belief Polaris is NOT the
brightest star in the northern hemisphere sky, in
fact it barely makes the top 50!!
Finding Polaris!
Much more important then Finding Nemo!
• Polaris is also called the North Star, or the
Load Star.
• Just look for the Big Dipper -- and notice
that the Dipper has a bowl and a handle.
Draw a line between the two outermost stars
in the bowl of the Big Dipper. This line
points to Polaris, the North Star!
Additionally:
Most stars rise and set -- just like the sun and moon. But
Polaris is like the hub of a wheel -- it stays put in the northern
sky, while all the other stars appear to circle around it (in fact
we are spinning on our axis and Polaris is centered above our
axis!)
Dividing up Earth’s Surface
• Latitude and Longitude are lines on the
globe that are used to determine location.
• Latitude is distance north or south of the equator,
measured in degrees.
• Longitude is distance east or west of the prime
meridian, measured in degrees.
Latitude is:
• The Angular distance
north or south of the
equator
• Parallel lines, equator
is zero degrees, north
pole is 90 degrees
north
• EQUAL TO
ALTITUDE OF
POLARIS!!!
LONGITUDE AND TIME
• Since longitude is determined
by taking the time of solar
noon (sun at maximum altitude
in the sky for the day) at your
location and comparing it to
solar noon at the prime
meridian.
• It is known that the Earth
makes one complete rotation
about its axis every 24 hours.
• 360 degrees divided by 24hrs
calculates to 15 degrees/hr.
Greenwich Time!
• If you know time at one location, you can say that
it is one hour earlier for every 15 degrees to the
west.
• Another way : The occurrence of any time moves
west at 15 degrees per hour.
• So when you measure your solar noon if it is 2:00
PM in Greenwich (on prime meridian) you know
you are 30 degrees west of Greenwich!
LONGITUDE IS….
• Angular distance east
or west of the prime
meridian
• Longitude lines are
not parallel, and get
closer together as you
move towards the
poles
• NOT determined by
the location of Polaris,
but another star –
THE SUN!
•Longitude lines run up and down (North & South) and
determine your location east or west of the prime meridian
• Latitude
lines run
east/west
and
determine
your
location
north, or
south of
the
equator