Download GEOCENTRIC AND HELIOCENTRIC MODELS

GEOCENTRIC AND HELIOCENTRIC MODELS
There are two ways the Earth’s position was explained by
scientific cultures.
 Geocentric means Earth-centred
 Heliocentric means Sun-centred
Scientists used to accept the geocentric model, but shifted to
accepting the heliocentric model, which led to a major shift in
scientific world views.
Notice how many planets are shown in the heliocentric model.
Why are Uranus and Neptune missing?
This is a great example of how scientific knowledge has
evolved in light of new evidence, and the role of technology
(telescope) in this evolution.
Here are some telescope images of planets:
Saturn
Jupiter
Venus
Back to Calculations…
As we touched on previously, astronomers have developed
convenient units of measure to accommodate and reduce
large distances to manageable numbers.
Interstellar (distances between the stars) are measured using
the light-year (l.y.). Since light travels about 9.5 trillion km per
year, this distance is considered one light year.
Astronomers have developed another useful unit for smaller
distances in space. In the solar system, for instance, the
standard unit of measure is the astronomical unit (A.U.),
which is the average distance between the Sun and the Earth
(about 1.5 x 108 km). This unit is better for measuring
distances between planets. For example, the distance from
the Sun to Jupiter is about 5.0 A.U.
Do the practice questions below (keep them, don’t hand them
in).
Here are some formulas to help you out:
To get light-years from km: light-years = km ÷ (9.5 x 1012)
To get km from light-years: km = light-years x 9.5 x 1012
To get A.U. from km: A.U. = km x 1.5 x 108
To get km from A.U.: km = A.U. ÷ (1.5 x 108)
1. A star is 6 light years away. How many km away is it?
2. A star is 25 trillion km away. How many light years away
is it?
3. Uranus is 19.218 A.U. from the Sun. How many km is
that?
4. Mars is 225 billion km away from the sun. How many
A.U. is that?
5. Venus is 0.7233 A.U. away from the sun. How many km
is that?
6. The closest Venus and Earth ever get is 39,630,000 km
away. How many A.U. is that?
7. Pluto is 5,916,000,000 km away from the Sun on
average.
a. How many A.U. is that?
b. How many l.y. is that?
8. The average distance between Neptune and the Sun is
30.06 A.U. How many light-years is that?