The Sun Dial

1
The Sun Dial

• Christine Griffin

2
What Is A Sundial?

• A sun dial is a way of determining the time of
  day by looking at a shadow made by the sun.
• Our planets revolve in ellipses around the sun
  and the shadow depicted on the dial allows us to
  judge what hour it is.
• The sun moves through a 15 arc in the sky every
  hour and stays at a constant rate, and a sundial
  that lies in the equitorial plane represents
  these angles.
• Sundials are often made for usage at 45 degrees
  north, but can be used for another latitude and
  adjusted.

3
What Is A Sundial- Cont.

• Sundials should be parallel to the Earths axis
  of rotation.
• Apparent solar time is the time told by the Sun,
  and mean solar time is the time told by our
  clocks. The difference between these times is
  about 15 minutes this difference is also known
  as the equation of time.
• To compensate for the equation of time issue, the
  dial can be adjusted or alterations to the actual
  face of the dial can be shown. Some dials have
  red representing summer hours and blue
  representing winter hours in order to do so.
• Also heliochronometer- corrects the time
  difference. Precision sundial.

4
www.sundials.org/faq/tips.htm
5
Terminology

• Gnomon the shadow-maker. Also sometimes called
  the style, although the style means something
  slightly different.
• Style the specific line that produces the shadow
  edge, which shows the time
• Dial face the surface upon which the shadow is
  cast
• Nodus a point on the edge of the gnomon that can
  also cast a shadow. Sometimes is in the shape of
  a small sphere.
• Hour lines show the position of the shadow at a
  given time

6
History

• Egyptians
• obelisks four-sided monuments-- in about 3500
  B.C.
• real sundial dates back to 2100 B.C.
• water-clock in 1500 B.C. --more accurate and
  remained in use until mechanical clocks
• Greeks and Romans also developed their own
• By 30 B.C. about 13 types in Greece, Asia Minor,
  Italy
• Later, an Arab, Abul-Hassan, introduced idea of
  making all hours of equal length in 13th century.
• Renaissance period marked lots of development of
  the actual features of the sundial
• Incorporated seasons, calendar date, sunrise,
  sunset, Zodiac signs etc
• Eventually clocks took over
• BUT until end of 19th century French railways
  used sundials to regulate their clocks

7
Types Of Sundials

• Noon Mark- sequence of noons
• Horizontal Dial- gnomon towards celestial pole.
  Hours and half-hours marked.
• Declining- can face directly towards N, S, E, or
  W. If East, only shows morning hours. If West,
  only shows afternoon hours.
• Reclining Inclining- set on a tilt.
• Vertical Direct North- face points directly
  North. Gnomon points to ground, parallel with
  axis of Earth.
• Portable- can be carried around places and
  adjusted

8
Sundials Today
Worlds Biggest Sundial at Jaipur Observatory, in
Jaipur, India. It is 27 meters high and accurate
to a fraction of a second.

• Some people have digital sundials
• Some people have analog sundials that just
  resemble a real sundial
• Most sundials today are of ornamental usage and
  people just put them in their gardens.
• Typically garden sundials have a face thats
  parallel to the ground.

9
Bibliography

• Early Clocks. A Walk Through Time. 28 Sept.
  2005 lthttp//physics.nist.gov/GenInt/Time/early.ht
  mlgt.
• The Equation of Time. NASS FAQ. 28 Sept. 2005
  lthttp//www.sundials.org/faq/tips.htmgt.
• Fraser, J. T. Time, The Familiar Stranger.
  Redmond Tempus Books, 1987.
• History of the Sundial. National Maritime
  Museum. 28 Sept. 2005 lthttp//www.nmm.ac.uk/serve
  r/show/conWebDoc.353/setPaginate/Nogt.
• Sundial. Sundial- Wikipedia. 28 Sept. 2005
  lthttp//en.wikipedia.org/wiki/Sundialgt.
• The Sun Dial Homepage. 28 Sept. 2005
  lthttp//www.qwerty.co.za/sundials/solar/solar.html
  gt.
• Watch and Clock. Encyclopedia Britannica.
  ELibrary. 28 Sept. 2005 lthttp//elibrary.bigchalk.
  comgt.