Equatorial Mounts

The varieties of equatorial mountings are limited only by the designer s imagination. The basic varieties, however, are the following  

Those that mount the tube to one side of the polar axis and use a counterweight on the opposite side to maintain balance. For an example, see Fig. 2. These are sometimes called off-axis or asymmetric mounts. It is also possible to mount a second telescope in place of the counterweight. 

Those that support the mbe on two sides in a balanced way to eliminate the need for a heavy counterweight. Yokes and forks are most commonly used, especially for larger telescopes. Theses are sometimes called symmetric 

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Pyrheliometer is an instrument that measures only the direct radiation from the solar disk itself, without bouncing off clouds or the atmosphere. Concentrating solar collectors utilize only this part of the total solar radiation. Its measurement gives an indication of the clearness of the sky. The normal incident pyrheliometer (NIP) measures this form of radiation. A tracker, called the equatorial mount, is used to keep the NIP pointed at the sun. The difference between the NIP and the total pyranometer readings is referred to as the diffuse solar radiation. 

The effects of weathering at locations such as Florida and Arizona can be accelerated by using panel mountings that track the sun, combined with metal Fresnel reflectors to concentrate the rays of the sun, water sprays and cooling devices. This method is known by the initials EMMAQUA which stand for equatorial mounted mirrors with water spray (AQUA). By such means, one year of normal Florida weathering can be achieved in approximately 40 to 45 days [4] and this is therefore a very cost-effective method for materials needing a long service life. 

EMMA Equatorial mount with mirror for acceleration... 

The samples are mounted on racks at an angle of 30-45° to the vertical in special frames facing south (equatorial mounts) (Fig. 10.125). It is also important to take into account the immediate environment in which the frames are placed because of the different reflectance of UV radiation and infrared absorption by earth, rock, concrete and asphalt. The height at which the frames are placed above ground level is also important. 

EMMA (equatorial mount with mirrors for acceleration) is designed to simulate arid conditions (ASTM D 1435 and ASTM E 838 cf. Table 10.29). 

Figure 9.4 Equatorial mount with mirrors for acceleration (EMMAQUA) testing. www.directindustry.com.

FIGURE 2 40-cm telescope on an off-axis equatorial mount [Courtesy National Optical Astronomy Observatories, Kitt Peak.]... 

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