A sundial at a particular
latitude in one hemisphere must be reversed for use at the opposite latitude in the other hemisphere
. A vertical direct south sundial in the Northern Hemisphere becomes a vertical direct north sundial in the Southern Hemisphere.
Do sundials go counterclockwise in the Southern Hemisphere?
Sundials in the southern hemisphere are
arranged counterclockwise
, where three O’clock is to the left of 12 O’clock. There, at noon, the sun is due north, but it still goes from east to west, and hence it moves counterclockwise. This is the opposite of what happens in the northern hemisphere.
What way does the shadow on your sundial move in the Southern Hemisphere?
Shadows will move in the opposite direction of the sun. In the Northern Hemisphere, they will move from west to east, and will point north at noon. In the Southern Hemisphere,
shadows will indicate south at noon
. With practice, you can use shadows to determine both direction and time of day.
How do you read a sundial in the Southern Hemisphere?
Sundials in the southern hemisphere are
arranged counterclockwise
, where three O’clock is to the left of 12 O’clock. There, at noon, the sun is due north, but it still goes from east to west, and hence it moves counterclockwise. This is the opposite of what happens in the northern hemisphere.
Does a sundial work on the equator?
There are many types of sundials; an equatorial sundial is easy to make and teaches fun- damental astronomical concepts. The face of the sundial
represents the plane of Earth’s equator
, and the stick represents Earth’s spin axis.
What direction should a sundial face?
Sundials need to point in the
direction of True North
, and the style (either a sharp straight edge or thin rod, often located at the edge or tip of the gnomon) must be aligned with the Earth’s rotational axis.
How accurate is a sundial?
A sundial is designed to read time by the sun. This places a broad limit of two minutes on accurate time because the shadow of the gnomon cast by the sun is not sharp. Looking from earth the sun is 1⁄2° across making shadows fuzzy at the edge.
The actual construction of a sundial can be very accurate
.
What are the disadvantages of sundial?
- A sundial doesn’t work at night.
- A sundial doesn’t work when the sun is hidden – by clouds, buildings, etc.
- A sundial only works at the latitude it is designed for – a sundial built for Ecuador woudl not be accurate in New Zealand.
What is the angle of a gnomon?
The gnomon of the vertical sundial makes an angle of
90°
–L with the vertical (that is, an angle L with the horizontal), as shown in the side view in Figure 5. In the southern hemisphere, the vertical dial is north-facing. Unlike the equatorial dial, the hour angles are not equally spaced.
How do you set up a sundial in Australia?
The gnomon, set to the correct latitude,
has to point to the true South in the Southern hemisphere
as in the Northern Hemisphere it has to point to the true North. The hour numbers also run in opposite directions, so on a horizontal dial they run anticlockwise (US: counterclockwise) rather than clockwise.
Do sundials work everywhere?
Sundials must be corrected across the span of a time zone
. Every zone has a “reference longitude,” and with every degree of longitude away from the reference, the sundial is off by an additional 4 minutes. Thus, equation of time correction is employed in order to maintain a uniform time across the zone.
Does a sundial work the same north and south of the equator?
To position a horizontal sundial correctly, one has to find true North or South.
The same process can be used to do both
. The gnomon, set to the correct latitude, has to point to the true South in the Southern hemisphere as in the Northern Hemisphere it has to point to the true North.
Who invented sundial?
The mathematician and astronomer Theodosius of Bithynia
( c. 160 BC to c. 100 BC) is said to have invented a universal sundial that could be used anywhere on Earth.
Does a sundial work at night?
In principle,
a sundial can also be used during the night
, provided that the moon is sufficiently bright and that the lunar age is known. The ‘solar time’ can then be obtained from the ‘lunar time’ (both expressed in equal hours) by adding four-fifths of an hour for each day of the lunar cycle.
How do you calculate a sundial?
- tan(theta) = tan(HA) x sin(lat)
- theta = the resulting dial hour angle measured from the noon line (- is left of the noon line, + is right of the noon line)
- HA = the hour angle of the sun from the noon meridian, expressed in (+/-) degrees.
Can you use a sundial on a cloudy day?
Sundials do not work at night or when it is very cloudy
. Even on a properly constructed sundial, several things reduce the sundial’s accuracy as a timekeeping tool.
