Thomsen Observatory

People gather inside the observatory and look up as they view the stars

Star Parties

Regularly scheduled viewing: first and third Friday nights of each month.  

If weather is marginal during the day, call the observatory at 817-202-6573 and leave a message with your questions and phone number.

Viewing begins about a half hour after sundown, but you are welcome to come before that, if you are patient for our volunteers to arrive to open the gate. Usually, we are setting up inside the dome about sunset. 

What to bring? Wear warmer clothes than normal daytime attire, especially in winter. As the air cools, viewing gets more clear, but so does shivering! In mosquito weather, bring bug spray. In winter, wear hats, gloves and other very warm clothing. It’s easy to remove layers to keep cool, difficult to add layers if you didn’t bring them. 
Also, your own lawn chair adds to your enjoyment if guests are waiting to view. Plan to stay an hour or more if viewing is optimal. 

Students smile as they gather around for a picture inside the observatory

Contact & Location

Thomsen Observatory: 817-202-6573
Address: 425 Linden St, Keene, TX 76059
Jerry Becker, Manager: 817-357-9097

Keene is 5 miles NE of Cleburne, TX,
8 miles SW of Alvarado,
25 miles S of Ft. Worth,
50 miles SW of Dallas and
65 miles N of Waco.

Basic Telescope Types

  • Refractor: Uses convex lens to focus image at eyepiece
    • Chromatic Refractor: Uses a secondary lens behind the primary to better focus the individual colors.
    • APOChromatic Refractor: Uses two secondary lenses to get the best focus of individual colors. The Thomsen scope is APOChromatic, the most accurate type of refractor telescope. This type of scope becomes expensive and heavy.
    • Galilio’s telescope, through which he discovered the first four moons of Jupiter, was a refractor with a small (about 3″) lens. 
  • Reflector: Uses a convex mirror to reflect light to a prism near the top of the scope which angles the light rays to the eyepiece. There are many variations of reflectors, and all large telescopes are reflectors (over about 40″) because a refracting lens becomes too large to maintain a consistent shape. 

Frequently Used Astronomy Terms – Wikipedia Descriptions

Viewing the Night Sky – Helpful Links to “Seeing”