Expansion Coefficient

The telescope must be focussed as the temperature changes due to the difference between the expansion coefficient of the telescope structure and that of the mirrors. If the support structure were made of glass, the focus would not need to be adjusted.

The expansion coefficient of aluminum is 22e-6 fraction/degree C. The expansion coefficient of the mirror is unknown, but most normal expansion glasses are around 9e-6. The height of the tower is about 62 inches therefore we calculate an net expansion coefficient of (22e-6 - 9e-6)x62=0.8 mil per degree C.

Last Updated 6/23/97 by RRT