satellite dishes - mirrors in the sky

"look, up in the sky ..

it's a bird ..
- it's a plane ...
  - no, it's a ... geosynchronous satellite !"

exploration lesson

visit satellite dish at south end of Buzzard Building.

concept introduction

satellites = objects that orbit planets
artificial satellites = devices put in orbit by space launches; travel 360 degrees every 90-ish minutes
geosynchronous satellite = orbits the earth every 24 hours; is synchornized with earth's rotation; so it stays over one spot; is about 22,300 miles high
ellipse = a ( slightly ) oval path that is the shape of orbits.
orbit = the path in which satellites / planets / comets / asteroids move, or ...
orbit = the time it takes a satellite to move 36O degrees. Also called a sideral period ( sidereal = star ).
revolution = the time it takes an object to move 36O degrees and then "catch up" with its original launch site which has rotated farther east ... or "ahead of it" -- while the satellite was orbiting. Also called a synodic period. What does the prefix ( syn ) mean ?
orbital speed: the larger the orbit, the slower the object moves.
- Astronauts --- about 90 minutes;
- geosynchronous satellites in 24 hours;
- the moon in a moonth (month)

concept application

orbits of satellites / planets / comets / asteroids
satellite communication: tv; telephone and even newspapers ( USA TODAY )
you see "ellipses" in a tilted, cylindrical drinking glass. The liquid touches the glass in an elliptical shape.

reference --- leyden's article:
The Elliptical John Kepler -- TST -- Nov 1984
Washington Educational Press Award: Best Science Feature Story of 1984

exploration phase
student make ellipses by using ...

[ 1 ] - push pins + cardboard + paper + string.
[ 2 ] - move the tacks farther / closer together and repeat.
[ 3 ] - what happens when you move the right / left tack ?
[ 4 ] - from any point on the ellipse, draw lines to the pin holes.
[ 5 ] - measure the total length of these two lines.
[ 6 ] - measure the longest line you can draw in the ellipse

concept introduction phase
ellipse ( definition ) =

is a plane (can be put on paper)
closed (not open)
curved (not straight)
line ...
such that the sum of two lines drawn from any point on the ellipse to fixed points call the foci ... is constant.

concept application phase
ooops ... this specific concept cannot be applied because the goal was to form a definition of an ellipse.
However, the activity leads kids to propose quantitative ( arithmetic ) definitions of other shapes.
A circle is a - - -

science background material

John Kepler [ l571-1630 ] developed three 'big ideas' of planetary motion ( which also describe motion of moons; asteroids; comets )

I. Big Idea of Elliptical Orbits Orbits have elliptical shapes.

II. Big Idea of Equal Areas In equal period of time ( a day; a week; a month ), a line connecting the sun-planet ( or a moon-planet ) sweeps out equal areas.

III. Cubed-Square Big Idea
When you cube the orbital period of a planet you have found the planet's distance from the sun, squared.

Jupiter's distance = 5.2 x earth's distance from sun, and ... Jupiter's period = l2 x earth's year

so: 5.2 x 5.2 x 5.2 = l2 x l2
distance, cubed ====== period, squared

Discussion:
Kepler couldn't explain "why" this 'cube-square thing' "worked" ... so this relationship is called "empirical" ... it's based on observational evidence but without an underlying theory. Years later, an Englishman name Newton ( first name, Fig ) explained this empirical discovery. The "why" was due to something called gravity.
p.s. Scientists must have patience - and persistence. It took Kepler 14 years to find this third 'big idea -- about 1605 to 1619.

see folder
"what is science" -- and read the item called 'science is a puzzle' -- for a discussion of 'empirical rules' of science

5 / 5w / 95
12 / 8f / 95