The Earth AsA Sphere
• Aristotle (4 BC) believed that Earth's sphrecity could be proven by careful visual observation.
• He moved from north to south and noticed that star pattern changes.
• He observed that sail ship disappeared from the hull view first.
• He also observed the circular shadow casted by the Earth on moon during lunar eclipse.
• Erastosthenes theory from 250 BC, the measurement of distance from Syene Well and
Alexandria, Egypt on July 21 when the day is summer solstice and the sun directly being
• Distance= 250,000 stadions >> 1 stadion = 200-210 yards
• His idea was best solution during 1600s but now we have GPS (Global Positioning System)
which is a constellation of 24 earth orbiting satellites that make it possible for people to
pinpoint geographic locations and elevations with a high degree of accuracy using ground
• Parallels and Meridians
◦ Astronomers before Erastosthenes placed horizontal line marking the equator and tropics
of Cancer and Capricon.
▪ ***Equator: formation of the circle around the earth that is equidistant from the north
and the south pole***
▪ ***Tropics of Cancer and Capricon: marking the northernmost and the southernmost
positions where the sun is directly overhead on the summer and winter solstices, such as
◦ Hipparchus (19—125BC) proposed that ***a set of equally spaced east-west lines called
parallels (HORIZONTALS) be drawn on maps.***
◦ He also added ***a set of north-south lines that are spaced equally at the equator and
converge at the north and south poles and are called the meridians (VERTICALS).***
• Latitudes and Longitudes
◦ Latitude on the spherical earth is the north-south angular distance from the equator to the
place of interest.
◦ Numerical ranges are from 0 deg at the equator to 90 deg at the poles.
◦ Longitude is the angle, measured along the equator, between the intersection of the
reference meridian, called the Prime Meridian (0 deg) and the point where the meridian for
the feature of interest intersects the equator.
◦ Numerical ranges are from 0 deg to 180 deg east and west of the prime meridian and are
twice as long as parallels.
◦ Putting latitude and longitude together, we get geographic coordinate (45 deg N, 120 deg
W) which helps us pin point a place on the earth's surface.
◦ BABYLONION SEXAGESIMAL SYSTEM of degrees(deg), minutes( ' ) , seconds ( '' )
◦ 1 deg = 60 minutes and 1 minute= 60 seconds
◦ Negative sign on Latitude means SOUTH and on Longitude means WEST