Bigger Mirror... Better Views - Hobbs Observatory Update!

By: Mike Brown, CVAS Volunteer and Local Astronomer

The large reflector telescope in the west dome at Hobbs Observatory features a 24-inch-diameter, 4-inch-thick quartz mirror. A mirror of this size gathers nearly 5,000 times more light than the unaided human eye, allowing us to see faint galaxies, glowing nebulae, and intricate lunar detail. Simply put, the bigger the mirror, the brighter and more detailed the view.
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A reflector telescope uses a mirror instead of a lens to collect light. Its concave surface has been precisely ground and polished to within millionths of an inch in the shape of a parabola. The front surface of the mirror is coated with an extremely thin layer of aluminum,  just 1/300th the thickness of a human hair,  which makes it reflective. The polished quartz itself is very stable, but the delicate aluminum coating slowly loses reflectivity over time. As that happens, image brightness and contrast decline. To restore peak performance, the old coating must occasionally be chemically stripped and a fresh layer of aluminum applied.

The Hobbs mirror was last recoated in 2005, so it was time for renewal. At the end of February, members of the Chippewa Valley Astronomical Society and the UW–Eau Claire Physics and Astronomy Department carefully removed the mirror, crated it, and shipped it to a recoating facility in California. The total cost for recoating, shipping, and insurance is estimated at $4,000, covered by UW–Eau Claire.

The refreshed mirror will be reinstalled and aligned in time for the start of the public observing season.

Hobbs Observatory is open to the public, free of charge, on clear Saturday evenings from May through October (except July 18 and September 12), beginning about an hour after sunset and continuing until 11:00 p.m. We invite you to visit this summer and see the universe come alive through the eyepiece.