Lesson 1 - Models of the Earth and Eratosthenes calculation of the circumference of the Earth

The models of the earth discussed in this material are flat earth model, geocentric model, heliocenteic model and geoheliocentric model.

1. HOW COME WE REALIZE THAT
THE EARTH IS NOT THE CENTER
OF THE UNIVERSE
PHYSICAL SCIENCE
QUARTER 4 –LESSON 1
KAREN MARIEL R. SABLE

3. MESOPOTAMIANS
asaccountedintheirmythology
around6thcenturyBCdescribedEarth
asaflatdiskfloatingintheoceanand
boundedbyasphericalsky.

4. Earth is spherical
SomeexplanationsaboutthesphericalEartharethenavigationandtheeclipse.

5. Geocentric model
TheEarthwasatthecenterandthe
restoftheplanetsandheavenlybodies
revolvedaroundit.

6. Geocentric model
TheEarthandotherheavenlybodieswere
assumedtobespheres.
Theywereconvincedthattheshapeofthe
Earthwasnotflatinsteaditwasspherical.
Thisideawasalreadyentertainedby
PythagorasandPlatohowevertheydonot
haveconcreteevidencetosupporttheir
claim.
Anaxagoras–explainedthattheEarthis
sphericalthroughtheoccurrenceof
eclipses

7. Geocentric model
Aristotle(around320BC),astudentofPlato
presentedhisargumentsthatestablishedthe
claimaboutthegeocentricmodelduringtheir
time.
Aristotlearguedthat:
-thesphereisperfectlysolidandtheheavens
arearegionofperfection
-theEarth'scomponentpieces,fallingnaturally
towardsthecenter,wouldpressintoaround
form
-inaneclipseoftheMoon,theEarth'sshadow
isalwayscircularthus,ifEarthisaflatdisc,it
wouldcastanovalshadow
-eveninshorttravelsnorthwardsthePoleStar
ishigherinthesky.

8. Heliocentric model
TheSunwasatthecenterand
therestoftheheavenlybodies
includingtheEarthmoved
aroundit.
Copernicusexplainedaboutthe
heliocentricmodel.

9. ACTIVITY!
Prepare ¼ sheet of paper.
1.)Whatisthe“flatearthers”
movementallabout?(minimumof2
sentences)
2.)Whatisthedifferencebetween
geocentricmodelandheliocentric
model?(minimumof2sentences)

10. Eratosthenes
HeisalibrarianatUniversityofAlexandria
inEgypt
Heapproximatelycalculatedthe
circumferenceoftheEarth.
Hecameacrossinformationthatduring
summersolsticeespeciallyatnoontime,
sunlightshinesdirectlydownadeepwell
inSyene,acitysouthofAlexandriaand
reflectedupagainandnoshadowiscast
byanyobjectonanoontime.

11. Eratosthenes
Withhismathematicalcalculations,he
calculatedthatthecircumferenceofthe
Earthis40,000km.
Withtheadvancetechnologynowadays,
thecorrectcircumferenceoftheearth
horizontallyis40,075kmand/or40,001
kmacrosstheearth’spole,whichisnot
farfromthecalculationofEratosthenes.

12. Eratosthenes
5,000 stadia is around 800 km.
7.2 degrees is about 1/50 of the full circumference of the earth.
7.2 degrees
5,000 stadia

14. Summary
Mesopotamians believe that the Earth is flat.
Pythagoras, Plato and Aristotle said that the earth is spherical.
Geocentric Model states that the Earth was at the center and the rest of the
planets and heavenly bodies revolved around it.
Heliocentric Model explains that the sun was at the center and the rest of the
heavenly bodies including the Earth moved around it.
Eratosthenes approximately calculated the circumference of the Earth.

15. ACTIVITY!
Prepare ¼ sheet of paper.
1.) To calculate the circumference of the earth,
Eratosthenes hired some people to measure the
distance between the column at Alexandria and the
well at Syene. Accordingly, the distance was about
5,000 stadia (800 km). He also measured the angle of
the column’s shadow at Alexandria which is 7.2° and
analyzed that it is the same angle of the distance
between the said places. What is the circumference of
the earth as calculated by Eratosthenes? Show your
solution.

16. Essay
In three to five sentences, answer the question:
Of all the arguments presented by the Greeks as proof that the Earth
is spherical, which among you find more convincing? Why?