More Related Content Similar to Presentation on Equation of time Similar to Presentation on Equation of time (20) 1. Presentation on
Equation of Time
Presented By:
Md. Nazmus Saqib Khan
ID 12075768
Year: 4th
Session: 2011-12
Department of Mathematics
University of Rajshahi-6205
4. Some Definitions
© Department of Mathematics, R.U.
Apparent sun: The sun we see in
the sky is called apparent sun.
Mean sun: The mean sun is
fictitious point which moves
uniformly along the equator with
the mean velocity of the sun along
the ecliptic.
5. Some Definitions
Apparent Solar Time:
Apparent solar time at any
instant is the time that has
elapsed since the preceding
apparent midnight. Apparent
midnight is the instant of the
sun’s lower transit on the
meridian.
Apparent solar time is equal
to the hour angle of the
apparent sun.
It is actually the time shown
by a sundial. (Fig.1)
Fig.1: Roman
Sundial© Department of Mathematics, R.U.
6. Some Definitions
Mean Solar Time: The
mean solar time at any
instant is the time that has
elapsed since the lower
transit of the mean sun. In
other words, the time
indicated by the mean
sun is termed as mean
solar time or simply mean
time. Mean solar time is
equal to the hour angle of
the mean sun. It is
actually our clock time.
(Fig.2)
Fig.2: Mechanical Clock
© Department of Mathematics, R.U.
7. Some Definitions
Transit: The instant
when any point on the
celestial sphere is on the
meridian of an observer
is called the transit or
culmination, of that point
over that meridian. When
it is on the half of the
meridian containing the
zenith is called upper
transit; when it is on the
other half it is called
lower transit.(Fig.3)
Fig.3: Transit
© Department of Mathematics, R.U.
8. Some Definitions
Hour Angle: It is the
angle subtended at the
pole between the
observer’s meridian and
the hour circle of the
body. In the northern
hemisphere, the hour
angle is always
measured from the south
towards the west upto
the hour circle of the
heavenly body. (Fig.4)
Fig.4: Hour angle
© Department of Mathematics, R.U.
9. Some Definitions
Right ascension: It is the
angular distance
measured from the vernal
equinox along the equator
to the point of intersection
of the equator with the
hour circle through the
body. It is measured from
the vernal equinox
eastwards from 0 to 360
degrees. (Fig.5)
Fig.5: Right Ascension
© Department of Mathematics, R.U.
10. Defining Equation of Time
Since observations made on the sun for the
purpose of determining the time can give
apparent time only, it is necessary to be able
to find at any instant the exact relation
between apparent and mean time. The
difference between the two, which varies
from -14m to +16m (nearly), is called the
equation of time. This quantity may be
found in the Nautical Almanac for each day
of the year.
© Department of Mathematics, R.U.
11. Defining Equation of Time
So the equation of time at any instant at a given place
is defined as the difference between the apparent
solar time and mean solar time at that instant.
Equation of time = Apparent solar time – Mean solar
time
= H.A. of apparent sun – H.A. of mean
sun
= R.A. of mean sun – R.A. of apparent
sun
Since, H.A. of a body = – R. A. of the body .
[H.A. = Hour Angle
R.A. = Right Ascension]
© Department of Mathematics, R.U.
12. Chief Causes of Equation of Time
The difference between the two kinds
of time is due to several causes, the
chief of which are:
I. The inequality of the earth’s angular
motion in the orbit, and
II. The fact that the apparent sun is on
the ecliptic while the mean sun is on
the equator.
© Department of Mathematics, R.U.
15. Some applications
The equation of time is used to correct the sundial time.
In the late 17th and 18th centuries, equation clocks were
made, which allowed the user to see or calculate
apparent solar time, as would be shown by a sundial.
It is also used for many applications of solar energy.
Machines such as solar trackers and heliostats have to
move in ways that are influenced by the equation of time.
Civil time is the local mean time for a meridian that often
passes near the center of the time zone, and may
possibly be further altered by daylight saving time. When
the apparent solar time that corresponds to a given civil
time is to be found, the difference in longitude between
the site of interest and the time zone meridian, daylight
saving time, and the equation of time must all be
considered.
© Department of Mathematics, R.U.
19. References
Spherical Astronomy by W. M. Smart
Practical Astronomy by George L.
Hosmer
Spherical Astronomy by Sharma
Astronomy by K. K. De
The Astronomical Almanac online
Wikipedia
Google Images
© Department of Mathematics, R.U.
20. END OF THIS PRESENTATION
Any Questions?
Thank You!
© Department of Mathematics, R.U.
