A coelostat is an solar tracking device consisting of a set of mirrors with one mirror driven by a clock to fixed the Sun image for a solar telescope. The solar image produced by a coelostat ["see-lo-stat"] during a day as the earth turns is not rotated.This image stability is achieved by using two flat mirrors with a polar rotating primary mirror. The primary mirror called the coelostat mirror is mounted on a polar axis with the mirror flat surface fixed parallel to the axis with its normal rotating perpendicular to the polar axis.The secondary mirror or second flat reflects the sun beam into the desired downward direction as in the case shown here.The height of the secondary remains fixed during a days observation but must be adjusted over the year to take into effect the variation of the solar declination as the suns position in the sky moves up and down over the celestial equator.The coelostat mirror can be moved radially from the east to west side of the secondary flat to avoid the secondary mirror obscuring the sun.The coelostat position can be set to minimizes the angles of incident to reduce the induced instrumental polarization.