Dean Ketelsen (1953-2023): A Personal Remembrance

Dean Ketelsen at the Grand Canyon Star Party

A dear friend of mine passed away suddenly last week while mowing the lawn at his cottage in St. Charles, Illinois. Most of us are lucky to have maybe a dozen friends. Dean must have had hundreds. He was as generous and kind-hearted as anyone I have ever known. And incredibly knowledgeable about observational astronomy and optics.

I first met Dean while I was an undergraduate student at Iowa State University in the late 1970s. He was hired by Dr. Willet Beavers to make stellar radial velocity observations using the 24-inch telescope at ISU’s Erwin W. Fick Observatory. I was the primary data analyst reducing the data from the telescope, and all of us were amazed at how many stars Dean could observe in a night! I believe Dean was the most productive observer Fick Observatory ever had.

Dean and I were part of the ISU team that traveled to a farm near Riverton, Manitoba, Canada to observe the total solar eclipse on February 26, 1979.

Iowa State University Solar Eclipse Expedition – February 26, 1979
Front Row (left to right): Dan Peterson, Maria Meyers, Chuck Hoelzen, Ed Sexauer
Back Row (left to right): David Oesper, Jim Pierce, David Cook, Mike Andrews, Prof. Stan Williams, Prof. Willet Beavers, Dean Ketelsen, Joe Eitter

After graduation and working for Fick Observatory before the radial velocity grant money ran out (temporarily), I moved to Dell Rapids, South Dakota to work for the EROS Data Center near Sioux Falls. But, before I left, Dean gave me a Unitron refractor. One of many examples of his generosity.

Soon after I moved to South Dakota, Dean moved to Tucson, Arizona to become a telescope operator on the Mayall 4-meter telescope at Kitt Peak National Observatory. Then, as now, the 4-meter scope was heavily scheduled, but on Christmas and New Year’s he sometimes had the scope to himself for photography and visual observing. I asked him once, “What is the most impressive object you ever saw with the Kitt Peak 4-meter?” His reply: “The crescent moon!” I received some beautiful black & white large prints of galaxies and nebulae from Dean taken with one of the large Kitt Peak instruments. I framed and cherished these astrophotos.

Dean left the telescope operator position at Kitt Peak a few years later and began working at the University of Arizona Mirror Lab where he remained for the rest of his life. He was directly involved in fabricating several of the 8.4-meter mirrors—the largest monolithic telescope mirrors in the world—as well as smaller optics as well. Early in his career at the Mirror Lab, Dean was also working part-time on a Master’s degree in Optical Science at the University of Arizona, but he was never able to complete it before classes he took more than five years earlier no longer counted towards his degree. And I can see why. Dean led a rich and busy life, and his many friends and acquaintances were always his first priority.

Dean’s hospitality was legendary. My family regularly visited Tucson over the years, and Dean was always a most gracious host, transporting us to see all the good sights whenever we visited. A tour of the Mirror Lab was often included, so—thanks to Dean—I have been there many a time.

Dean’s generosity was also legendary. Besides the Unitron refractor and astrophotos, many years ago Dean “loaned” me a pair of Fujinon 16×70 binoculars, and after I moved to Tucson in 2022, he gave me a pair of Celestron 25 x 100 binoculars as a house-warming gift, no longer following any pretense that this would be a loan.

Over a several year period, Dean made a 24-inch mirror for the Ames Area Amateur Astronomers in Iowa, which they are still using today in a Dobsonian telescope built by club members. And, speaking of Dobsonians, Dean was a close acquaintance of John Dobson, and they often got together at star parties.

Dean Ketelsen with John Dobson at a star party

Here are some recent examples of Dean’s generosity. When Suzy and I came to Tucson to visit December 26-30, 2021, Dean and his dear friend Susan Yager picked us up at the Amtrak station and they both spent a lot of time with us as we were thinking about moving to Tucson. Ditto for our March 6-10, 2022 house-hunting trip. I was planning to take Amtrak back to Wisconsin with a stop in Alpine, TX to visit my daughter and her family while Suzy flew to Chicago to get back to work sooner, but Dean was driving from Tucson to St. Charles, Illinois so I rode with him. Though he didn’t have to, Dean went out of his way to drop me off in Dodgeville, Wisconsin and then went on to St. Charles.

Before that house-hunting trip, Dean had reached out to the relatives in charge of Derald Nye’s estate, knowing that I would be losing my backyard research observatory in Wisconsin and that it might be possible for me to purchase his home in Corona de Tucson, which would include an observatory. Unfortunately, that opportunity did not happen, but Dean subsequently put in a good word for me so that I could serve on the 16-inch Meade telescope committee which will add that telescope to the TAAA’s TIMPA observing site.

Before we moved to Tucson, Dean offered to transport my astronomical optics in his large van so that I didn’t need to entrust that delicate equipment to the movers. A week before moving, we drove from Dodgeville and he drove from St. Charles where we met up in Rockford at Lino’s for pizza (great restaurant!) and the transfer of optical equipment to his van afterwards. Needless to say, that equipment arrived safe and sound and in perfect condition at our new house just a few days after the movers when Dean made the trip back to Tucson.

After we moved to Tucson on May 1, 2022, besides restaurant get-togethers at Daily Mae’s and Bianchi’s, Dean & Susan joined John & Lana Gilkison at our house to observe the May 15, 2022 total lunar eclipse. Dean (and Susan) picked me up twice for dark-sky observing: once to watch the Tau Herculid meteor shower Memorial Day 2022 at his favorite observing spot along the road to the top of Kitt Peak, and once to observe from Empire Ranch SSE of Tucson. I was looking forward to many more observing sessions with Dean, but sadly that will not happen. I have lost my best observing buddy here.

No one person can relate all the accolades and experiences that Dean had, but I know of a few. Dean received the 2002 Las Cumbres Amateur Outreach Award from the Astronomical Society of the Pacific, and the asteroid 124075 Ketelsen (2001 GT1) was named after him.

Dean Ketelsen receiving the 2002 Las Cumbres Amateur Outreach Award
from the Astronomical Society of the Pacific

Dean was primarily responsible for reincarnating the Grand Canyon Star Party in 1991. He was a primary organizer for many years, and I believe he had attended every year since, including this year. I had the good fortune to attend in 2006, and gave one of the “Twilight Talks”. The most wonderful aspect of this star party that makes it very special and decidedly different from other star parties I have attended is that thousands of enthusiastic visitors to Grand Canyon National Park from all around the world are regaled by a twilight talk each night followed by observing through nearly 50 telescopes, binoculars, and green-laser-pointed constellations and satellites. The enthusiasm of the amateur astronomers sharing their love of astronomy with folks who are in an unusually good mood because they’re on vacation in a beautiful place is a winning combination. Dean had a lot to do with that vibe!

Dean was also an excellent public speaker, and frequently gave public astronomy talks and talks about the exciting things happening at the Mirror Lab.

Joan Oesper, Dean Ketelsen, Melinda Ketelsen, and David Oesper at Yerkes Observatory in 2008

Dean was an incredible photographer, whether the subject was astronomical, terrestrial, or people. He and his wife Melinda, who passed away after a long battle with cancer in 2016, have a blog called The Ketelsens! that includes many of his photos and descriptions of many of their experiences through the last posting on May 31, 2020—during the COVID-19 pandemic. I sincerely hope this blog will be moved to a permanent location on the internet before his blogspot account runs out. It would be a terrible shame to lose this treasure!

And, speaking of photography, Dean first suggested many years ago the idea of stereo photography of the aurora. To the best of my knowledge, this has seldom been done, though with cellular phones and digital cameras now it would be relatively easy to coordinate such a venture. Two observers separated by a hundred miles or more with identical cameras, lenses, and exposure times would need to take pictures of the aurora at exactly the same time and in exactly the same direction (centered on the same star or constellation). The results, I’m sure, would be spectacular!

I have found it difficult to capture all I want to say about Dean in this article, but I’d like to finish by sharing with you the recent email communications I had from Dean, right up to the day before he died. All but one of my emails to Dean are unimportant in the context of this article, so they are not included here.

June 4, 2023 email from Dean Ketelsen
Just got word from Elinor’s niece Cathy (Prescott) that Elinor died a couple weeks ago.  Evidently fell and broke her arm in several places, contracted pneumonia and died a week later.  So sad – about the last of that generation of friends.  She and David Levine, Derald Nye, Mike Terenzoni and I were the only folks (and Vicki!) at Grand Canyon #1.  No memorial is planned, but I’ve already asked thru Cathy for a vial of her ashes – maybe we can have our own at the Canyon next year!

July 26, 2023 email from Dean Ketelsen
Hi David-
How are you surviving the heat?  I’ve been up in St Charles coming up on 4 weeks and it has been delightful!  This week is the worst, supposed to be up over 90, I think for the first time, tomorrow and Friday before dropping to low 80s for the weekend.  I love those sunny days in the 70s, though we have been getting some smoke from the Canadian fires, some days worse than others.

The closer it comes, the less I’m excited about the annular eclipse.  Plus I’ve got a “Ketelsen reunion” on 8 October, and after driving to the Midwest, not sure I’m up for returning after less than a week!  So may watch the partial phase from here.  Still thinking about next April.  My first wife Vicki’s sister and her family live in Dallas and am welcome there.  I’ve sent them a map of the path and they are looking for a location closer to the center line for a small group.  Will see what they come up with.  Not sure I’m interested in trying to chase clear spots – again, will see what sort of a zoo it is!

Probably back in Tucson about the weekend of the 12th.  Hopefully temp will have dropped a little towards normal!

Hang in there!


August 5, 2023 email from Dean Ketelsen
Hi David-
This article caught my eye in NYT online site.  The hospital mixup was only a few miles from Riverton where we observed the ’79 solar eclipse…

Dean texted me about a Space X rocket launch from Vandenberg on August 7. I called him and we talked briefly on the phone. Little did I know it would be the last time I would hear his voice. Then, he sent me this email:

Good Luck! <> on behalf of Launch Alert <>
Sent: Monday, August 7, 2023 1:02 PM <>
Subject: [EXT][Launch Alert] Launch on Schedule

External Email

Tonight’s launch of a Falcon 9 rocket from Vandenberg SFB appears to be on schedule. The following is an update from SpaceX:

“SpaceX is targeting Monday, August 7 at 8:57 p.m. PT (03:57 UTC on August 8) for a Falcon 9 launch of 15 Starlink satellites to low-Earth orbit from Space Launch Complex 4 East (SLC-4E) at Vandenberg Space Force Base in California.”

For launch and countdown status, go to…

August 7, 2023 email from David Oesper to Dean Ketelsen
Hi Dean,
Thanks for letting me know about this.  We had partly cloudy skies tonight, which didn’t help, and I had to observe from my patio so if, as I suspect, the launch would only have been visible close to the WNW horizon, I wouldn’t have been able to see it.  I thought I might be able to see one of the stage separations as it was heading to our southern sky here, but no luck with that either.  Oh well, it was worth a try, anyway.



August 8, 2023 email from Dean Ketelsen
Hey David-
Watching the launch online, I could see the sunset from the onboard camera, but I don’t think it ever rose into bright sunset.  Still, Ben Bailly of TAAA captured the enclosed last night.  Still, not as spectacular as what it could be – the second taken be non-astronomer friend from Sabino Canyon area 10 months ago she noticed w/o advance warning…. Better luck next time!


Dean died the following day. Here is his obituary:

Dean’s obituary states that there will be a future gathering in Tucson to celebrate Dean’s life. As soon as that event is announced, I’ll post the information here in a comment.

Dean Ketelsen – Public Star Party at Sabino Canyon – April 29, 1989

I encourage you to share your personal remembrances of Dean by posting a comment here.

5 thoughts on “Dean Ketelsen (1953-2023): A Personal Remembrance”

  1. I hadn’t heard that. I’m surprised nothing came out from the TAAA.
    Great guy who contributed greatly to the astronomy community down here in Tucson for sure.

  2. A memorial service for Dean Ketelsen will be held at the Steward Observatory on the University of Arizona campus, 933 N. Cherry Ave. in Tucson on Sunday, October 1 at 1:30 p.m. MST.

    1. Thanks for your remembrance, David!

      Yes, the TAAA will publish a tribute to Dean in its Sept. newsletter. And Steward observatory will host a Celebration of Life on 1-Oct-2023, as David said, in the large lecture hall (Room N210), at 1:30 pm. The date has been selected so as not to collide with football games, and the high temperature on the mirror casting for GMT7. Dean wouldn’t want that! Also, his many friends and family members need time to travel from far away.

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