Changing Planet

World’s Largest Backyard Telescope

Some 35 feet tall and housing a 70 inch diameter mirror, this may be the largest amateur-built telescope on the planet today. Credit: Steve Dodds

Ask any backyard stargazerbigger is better when it comes to telescopes. One Utah amateur has turned just such a towering dream into reality.

Truck driver by day and passionate skywatcher by night, Mike Clements has built what appears to be the world’s largest modern-day amateur telescope.  The behemoth telescope has a primary mirror measuring 70 inches (1.8 meters) across. It is housed in a black metal cage that stands some 35 feet (10.7 meters) tallthe size of a school bus.

For comparison, the most popular sizes for backyard telescopes typically range anywhere from 3 to 12 inches (7.6 to 30.5 centimeters).

At the heart of Clements’ reflecting telescope is the 900-pound (408 kilograms) mirror, one made originally for a U.S. spy satellite program. However due to some minor damage during manufacturing, the mirror was mothballed, and eventually put up for auction, which is how Clements acquired it in 2005, according to press reports .

Telescope builder Mike Clements poses in front of the massive 70 inch wide mirror at the heart of his giant reflecting telescope. Credit: Steve Dodds
Telescope builder Mike Clements poses in front of the massive 70 inch wide mirror at the heart of his giant reflecting telescope. Credit: Steve Dodds

The larger the aperture (or diameter) of the primary mirror (or lens) that collects  incoming light in a telescope, the better its image qualitywhether you view the moon, planets or distant stars. That’s why many amateur astronomers acquire what’s called “aperture fever”, always wishing for a bigger telescope.

Alongside the financial aspects, however, factors such as portability , storage and ease of use bring most stargazers down to Earth when choosing a telescope for tours of the cosmos.

Technically, the record for largest amateur-made telescope may still go to Ireland’s Lord Rosse, who in 1845 built a 72-inch-telescope that stood as the largest astronomical instrument in the world for many years.

Clements plans to eventually take his dream scope on the road, touring the country and letting the public gaze up at the cosmos up close.

I bet long lines will form for folks hoping to get a peek through this monster telescope.


Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • Heriberto Villarreal

    I will like to know if the telescope worked and the range

  • m salganik

    apparently it does… still needs some work but there have been very positive observing reports. Check out the forums at where there have been several threads discussing this scope (with first-hand observing reports).

  • Paul Manhart

    Couple of comments in description:
    1. Diameter decreases angular resolution (diffraction limit), but telescope must be fabricated well and not change shape from one position to another. Also, at that aperture atmosphere will limit resolution. You need adaptive optics dude! I know that you know all this but description seemed a bit simple.
    2. My friend Pete Schwar built a large telescope with a seat attached so he was always at the eyepiece. Used car battery to slew telescope. Won award for this at the Riversude Telescope Conference (Big Bear CA) around 1981 or 82. Check it out.
    3. With ladder, viewing for line of people will be a problem. Any solutions here?
    4. Looks like a Ritchey from the size of the obscuration. Am I right?
    5. Fantastic job. Keep us all posted. Try getting a trailer for transportation.

    Where in the country are you?

  • Rodger Fry

    I am the director of the Stansbury Park Observatory Complex in Tooele County, Utah. We made an agreement with Mike Clements to house this telescope in a building we built. We have had it up and running for 3 month and I can testify that the resolution is superb. It is effected by unstable atmosphere but when the seeing is good it is fantastic.
    We have purchased two viewing platforms that the public can walk up the stairs view and then walk down the second set of stairs.
    We try to make special arrangements for guests coming in from out of town to open up the facility for them

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.

Voices director: David Braun (

Social Media