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日ial是一个使用太阳位置的时钟，一根杆子在时间线上的飞机上投下阴影。

  晷

  坐标

  Declination of wall

  Local constant

  Equation of time and analemma

  Build a sundial manually

  评论

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晷





 日ial是基于对太阳位置的检测来测量时间的仪器。有非常古老的起源，在其最一般的意义上表示建筑物墙壁上的日。。是由触笔组成，称为gnomon，它是把它的阴影在表盘（或表盘）上的杆允许计时。在拨号小时线中绘制相应的小时。
日ial可以根据特定的纬度进行裁剪，使得gnomon平行于地球的旋转轴线，使其指向北半球的北极和南半球的南极。
日The的研究被称为gnomonic。
要建立日ial，您需要知道：
  坐标，纬度和经度
  倾斜墙
 本地常量
  ;时间方程
此信息的准确性将决定日the的准确性。

使用easy软件在几分钟内构建太阳表盘，单击链接：建立日。


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坐标

The earth’s coordinates, latitude is the angle between the equatorial plane and the straight line that passes through that point and is normal to the surface and longitude the angle east or west from a reference meridian to another meridian that passes through that point.
Is very important to calculate it accurately (up to 6 decimal places) to get a more accurate sundial, you can use this tool, find your home, zoom in and move the marker over your wall.

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Declination of wall

The declination of a wall is the angle in degree between the south and perpendicular axis of the wall (north for the southern hemisphere), is counted positive towards West and negative towards East.
There are more method to calculate the declination, let’s see some:

compass method

A compass indicates the direction of the magnetic pole, but there can be several errors in the measurement, bisurbation like mountains. You can use a easy tool 在地图上测量 select distance mode, move the marker over the wall use max zoom and click to get a second marker parallel to the wall, read the value of the direction and add 90 degrees to get the declination

shadow method

Get the sun position with this tool 太阳位置 set coordinates date and time (accurately around noon), move the mouse over the sun icon and read the azimuth and elevation, whit this data you can calculate the shadow of a nail, the the difference (theory for south and real value) in degrees is the declination

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Local constant

It is equivalent to the difference of time, early or late, between the meridian passage of the sun (time zones which are adjusted our watches, 15° every hour), and that the longitude of the sundial.

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Equation of time and analemma

The dials do not convert the common apparent solar time in standard time. It therefore has a variation of 15 minutes in a year, known as the equation of time, caused by the fact that the Earth’s orbit is elliptical and not circular, and is inclined with respect to the equator (see ecliptic)
The visual representation of this equation is the analemma, in astronomy indicates a particular geometric figure-eight curve that describes the position of the sun on different days of the year, at the same time and in the same locality.
Due to the tilt of Earth’s axis ( 23.5° ) and ellipticity Earth’s orbit, the height of the Sun above the horizon is not the same, day after day, and the combined effect is that of the figure described. The vertical coordinate of each point corresponds to the declination of the Sun at that time, while the horizontal coordinate indicates the deviation of the solar position earlier or later than the average time ( as shown by the clocks ) .
A Simple Expression for the Equation of Time:
n = day of the year.

Δt = 9.873 sin( 4π / 365.242 ( n - 81 )) - 7.655 sin( 2π / 365.242 ( n - 1 ))

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Build a sundial manually

The most important element of the sundial is the gnomon, which consists of a rod that casts its shadow on a sundial on which the hour lines must be drawn. By the type of sundial (vertical, horizontal, equatorial ring, etc.), the size, from the coordinates and from the declination determines the length and its position.



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