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Äàòà èçìåíåíèÿ: Wed Apr 18 01:38:12 2007
Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 17:34:02 2007
Êîäèðîâêà:
Ïîèñêîâûå ñëîâà: http astrokuban.info astrokuban

rotaPlatToSky

Converting platform rotation to rotation on the sky

apr07
The platform can be rotated by pulling on the tie downs or redistributing weight on the platform. The picture below shows the different parts of this
rotation:

rotating the platform about the main cables.

rotating the platform about the main cables.

The rectangle is the platform. The arc is the paraxial surface
The black lines are before the rotation, the red lines are after the rotation.
The rotation is about the bottom of the platform where the main cables attach.
The blue dashed lines go from the center of rotation to the horn (sitting on the paraxial surface). The horn rotates through the same angle as the platform.
The green dashed lines go from the center of curvature of the reflector to the horn. This is about 435 feet.
The center of rotation of the platform is about 61 feet above the paraxial surface.
The purple line is the path the horn moves during the platform rotation.

The distance the horn moves increases as the zenith angle increases. The sky angle is the purple distance divided by 435 feet. The platform angle is the distance divided by the blue line. The sky rotation will be about 6 times smaller than the platform rotation because of the ratio of the distances.

The picture below shows the ratio of SkyRotationAngle/PlatFormRotationAngle as a function of zenith angle:

SkyAngle/PlatformAngle vs za

The ratio changes because the distance from the center of rotation of the platform to the horn changes with za.
The idl routine platrotosky will compute the positions of the horn as the platform rotates as well as the rotation angle on the sky.

processing: x101/070114/cmptilt.pro
See Also: the idl routine pnt platrotosky

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