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Maps Union County
College is located at 40 degrees, 40 minutes North Latitude Newark AP 40° 42' N 74° 10' W
http://www.worldatlas.com/aatlas/imageg.htm LATITUDE
& LONGITUDE ********************* David P. Stern, “From Stargazers to Starships”—Site Map presents a series of Web pages on astronomy, geography, physics, mathematics, and space travel. Available online at http://www-istp.gsfc.nasa.gov/stargaze/Smap.htm. His page dealing with latitude and longitude has been edited below. If this is a NASA site, the material should be public domain. Making Maps This material is
taken from: Parallels of Latitude
Imagine the Earth was a transparent sphere (actually the shape is slightly oval; because of the Earth's rotation, its equator bulges out a little). Through the transparent Earth (drawing) we can see its equatorial plane, and its middle the point is O, the center of the Earth. To specify the
latitude of some point P on the surface, draw the radius OP to that point. Then
the elevation angle of that point above the equator is its latitude λ--northern
latitude if north of the equator, southern (or negative) latitude if south of
it.
On a globe of the Earth, lines of latitude are circles of different size. The longest is the equator, whose latitude is zero, while at the poles--at latitudes 90° north and 90° south (or -90°) the circles shrink to a point. Longitude
On the globe, lines of constant
longitude ("meridians") extend from pole to pole, like the segment
boundaries on a peeled orange. Every meridian must cross the equator.
Since the equator is a circle, we can divide it--like any circle--into 360
degrees, and the longitude φ of a point is then the marked value of that
division where its meridian meets the equator.
Longitude lines or "meridians" What that value is depends of course on where we begin to count--on where zero longitude is. For historical reasons, the meridian passing the old Royal Astronomical Observatory in Greenwich, England, is the one chosen as zero longitude. Located at the eastern edge of London, the British capital, the observatory is now a public museum and a brass band stretching across its yard marks the "prime meridian." Tourists often get photographed as they straddle it--one foot in the eastern hemisphere of the Earth, the other in the western hemisphere. A lines of longitude is also called a meridian,
derived from the Latin, from meri, a variation of "medius" which
denotes "middle", and diem, meaning "day." The word once
meant "noon", and times of the day before noon were known as
"ante meridian", while times after it were "post meridian."
Today's abbreviations a.m. and p.m. come from these terms, and the Sun at noon
was said to be "passing meridian". All points on the same line of
longitude experienced noon (and any other hour) at the same time and were
therefore said to be on the same "meridian line", which became
"meridian" for short. About
time--Local and Universal
Two important concepts, related to latitude and (especially) longitude are Local time (LT) and Universal time (UT)
Local time is actually a measure of the position of the Sun relative to a
locality. At 12 noon local time the Sun passes to the south and is furthest from
the horizon (northern hemisphere). Somewhere around 6 am it rises, and around 6
pm it sets. Local time is what you and I use to regulate our lives locally, our
work times, meals and sleep-times.
But suppose we wanted to time an astronomical event--e.g. the time when the 1987
supernova was first detected. For that we need a single agreed-on clock, marking
time world-wide, not tied to our locality. That is universal time (UT), which
can be defined (with some slight imprecision, no concern here) as the local time
in Greenwich, England, at the zero meridian. Local
Time (LT) and Time Zones
Longitudes are measured from zero to 180° east and 180° west (or -180°), and both 180-degree longitudes share the same line, in the middle of the Pacific Ocean.
As the Earth rotates around its axis, at any moment one line of
longitude--"the noon meridian"--faces the Sun, and at that moment, it
will be noon everywhere on it. After 24 hours the Earth has undergone a full
rotation with respect to the Sun, and the same meridian again faces noon. Thus
each hour the Earth rotates by 360/24 = 15 degrees.
When at your location the time is 12 noon, 15° to the east the time is 1 p.m.,
for that is the meridian which faced the Sun an hour ago. On the other hand, 15°
to the west the time is 11 a.m., for in an hour's time, that meridian will face
the Sun and experience noon.
In the middle of the 19th century, each community across the US defined in this
manner its own local time, by which the Sun, on the average, reached the
farthest point from the horizon (for that day) at 12 oclock. However, travelers
crossing the US by train had to re-adjust their watches at every city, and long
distance telegraph operators had to coordinate their times. This confusion led
railroad companies to adopt time zones, broad strips (about 15° wide) which
observed the same local time, differing by 1 hour from neighboring zones, and
the system was adopted by the nation as a whole.
The continental US has 4 main time zones--eastern, central, mountain and
western, plus several more for Alaska, the Aleut islands and Hawaii. Canadian
provinces east of Maine observe Atlantic time; you may find those zones outlined
in your telephone book, on the map giving area codes. Other countries of the
world have their own time zones; only Saudi Arabia uses local times, because of
religious considerations.
In addition, the clock is generally shifted one hour forward between April and
October. This "daylight saving time" allows people to take advantage
of earlier sunrises, without shifting their working hours. By rising earlier and
retiring sooner, you make better use of the sunlight of the early morning, and
you can enjoy sunlight one hour longer in late afternoon. The
Date Line and Universal Time (UT)
Suppose it is noon where you are and you proceed west--and suppose you could travel instantly to wherever you wanted.
Fifteen degrees to the west the time is 11 a.m., 30 degrees to the west, 10
a.m., 45 degrees--9 a.m. and so on. Keeping this up, 180 degrees away one should
reach midnight, and still further west, it is the previous day. This way, by the
time we have covered 360 degrees and have come back to where we are, the time
should be noon again--yesterday noon.
Hey--wait a minute! You cannot travel from today to the same time yesterday!
We got into trouble because longitude determines only the hour of the day--not
the date, which is determined separately. To avoid the sort of problem
encountered above, the international date line has been established--most of it
following the 180th meridian--where by common agreement, whenever we cross it
the date advances one day (going west) or goes back one day (going east).
That line passes the Bering Strait between Alaska and Siberia, which thus have
different dates, but for most of its course it runs in mid-ocean and does not
inconvenience any local time keeping.
Astronomers, astronauts and people dealing with satellite data may need a time
schedule which is the same everywhere, not tied to a locality or time zone. The
Greenwich mean time, the astronomical time at Greenwich (averaged over the year)
is generally used here. It is sometimes called Universal Time (UT). http://www-istp.gsfc.nasa.gov/stargaze/Slatlong.htm This Web pages continues to give an introduction to Star Maps. For an image of a Star Map go to this site: http://csep10.phys.utk.edu/astr161/lect/time/maps.html |
![[IMAGE: Defining latitude]](maps.h4.gif)
![[IMAGE: Lines of latitude]](maps.h5.gif)
![[IMAGE: lines of longitude]](maps.h6.gif)