Astronomical rings

The term ring sundial is used several times:

• Most of the portable sundial in the form of an annular equatorial sundial, but with adjustable Nodus is meant instead of a Polstabs.

• An annular equatorial sundial with scale on a ring instead of on a plane is also briefly mentioned sundial.
• The farmer ring is sometimes referred to as a simple sundial. There are farmer rings that have only the size of a finger ring, which may be another reason to call him sundial.

Equatorial sundial

Bauer ring

The portable sundial

The portable sundial is similar in the unfolded state of use of a stationary annular equatorial sundial. It has the form of a reduced two rings armillary sphere. However, in contrast to Äquatoralsonnenuhr she has a Nodus instead of a Polstabes and functions as height sundial. This is set to the polar axis as a function of the declination of the sun ( year date) and is mostly designed hole shaped.

Principle of operation

In the function as height sundial the height of the sun above the horizon but its elevation is not meant as usual on the celestial equator. This angle is identical to the angle of declination of the sun, practically does not change throughout the day. The equatorial scale ring represents the celestial equator, the right set Nodus the sun. So that the solar beam is incident on the equator of the ring, this is to rotate together with the ring about the vertical axis sundial. The beam impinges on the mark, indicating the time of day. At the same time, the sundial is " facing north " could be fixed as a local fixed equatorial sundial. The outer ring is located in the plane of the sky meridian.

Since there are two ways out of the truth noon, that the light spot falls on the scale ring, you must know whether morning or afternoon is. The clock is used the fastest correct if one makes sure that the light spot in the morning to the right ( looking at the clock so that you look along the sliding rod from top to bottom ), in the afternoon falls to the left. Around noon, the light spot hits the scale ring only grinding. The measurement accuracy is now at its lowest: error about ± 5 minutes. On True lunch itself is possible because of the drop shadow of the outer ring no reading. At the equinoxes, there is no light spot, because the scale ring of shadows.

Use

• The latitude of the use - map is set on the outer ring by the suspension loop is moved to the corresponding width value.
• The hole slider to the year date in the setting rod.
• The free hanging sundial is held horizontally rotated until the sunlight through the hole on the line on the inside of the inner ring Areas Covered ( scale ring ) falls ( note whether morning or afternoon is ). The sliding rod is rotatable about its axis, can be so getting worried for a full light spot.
• When you spot the true local time is read from the hour scale.