Download LAB1_1SEP09

A sextant is used to measure the angle between the
horizon and sun, moon, Venus, or North Star
Used (before
GPS) for
navigation,
especially at sea.
Latitude can be
determined
directly (at noon)
Longitude requires
accurate
timekeeping.
Analema
Due to the slightly
elliptical orbit of
the Earth around
the sun, the sun is
not directly south
at local solar
noon. The Earth
is closest
(perihelion) in late
December/early
January.
The prime meridian is an imaginary line from pole
to pole passing through Greenwich England
Royal Greenwich Observatory
Although the date line
is nominally at 180°
longitude from
Greenwich, it has
various jogs to avoid
day changes inside
countries (USSR for
instance.) The latest
jog put Eastern
Kirabati in the Eastern
segment.
What precision is required?
The distance between two points lying on the
same longitude that are separated by 1° of
latitude is 111 km.
One degree is not precise enough for most
purposes. One-tenth of a degree will probably
get you to a city or its suburbs (11 km).
Google Earth displays latitude and longitude in
degrees and minutes. Write that value down for
the various cities in your lab sheet and then
convert to fractional degrees.
The formula below may be used to
convert coordinates from
(deg,min,sec) to decimal degrees
fdecimal deg rees = fdeg rees +
fmin utes +
fsec onds
60
60
Local time may be determined from
UTC by the formula below. Round
the result to get zone standard time.
Tlocal = UTC +
Longitudedeg rees East
15