Land of the Long Twilights

The first (and only!) sunset1 this year at Amundsen–Scott South Pole Station in Antarctica occurs on March 22 at 0615 UTC (using “astronomer’s time” as time zone has no meaning so close to the South Pole).

The year’s first and only end of civil twilight (when the geometric center of the Sun lies 6° below the horizon) occurs on April 4 at 1153 UTC. That’s 13d05h38m after sunset.

The year’s first and only end of nautical twilight (when the geometric center of the Sun lies 12° below the horizon) occurs on April 21 at 0409 UTC. That’s 16d16h16m after the end of civil twilight.

The year’s first and only end of astronomical twilight (when the geometric center of the Sun lies 18° below the horizon) occurs on May 11 at 0521 UTC. That’s 20d01h12m after the end of nautical twilight, and 49d23h06m after sunset. That’s one heck of a long twilight!

Night lasts from May 11 at 0521 UTC until astronomical twilight begins on July 31 at 1916 UTC. A duration of 81d13h55m.

Nautical twilight begins on August 21 at 0024 UTC. That’s 20d05h08m after the beginning of astronomical twilight.

Civil twilight begins on September 6 at 2121 UTC. That’s 16d20h57m after the beginning of nautical twilight.

The first and only sunrise of the year occurs on September 20 at 0945 UTC. “Morning” twilight lasts a total of 50d14h29m.

The Sun remains above the horizon continuously until sunset on March 22, 2025 at 1100 UTC. Daylight “hours” last 183d01h15m.

Strange place!

1Sunrise and sunset. For computational purposes, sunrise or sunset is defined to occur when the geometric zenith distance of the center of the Sun is 90.8333 degrees. That is, the center of the Sun is geometrically 50 arcminutes below a horizontal plane. For an observer at sea level with a level, unobstructed horizon, under average atmospheric conditions, the upper limb of the Sun will then appear to be tangent to the horizon. The 50-arcminute geometric depression of the Sun’s center used for the computations is obtained by adding the average apparent radius of the Sun (16 arcminutes) to the average amount of atmospheric refraction at the horizon (34 arcminutes).
[Reference:, but see here:]

Note: SkySafari 6 Pro, Version 6.8.2 (6820) for MacOS was used to determine these dates and times. The location coordinates used for Amundsen–Scott South Pole Station were 89° 58′ 59.9″ S, 139° 16′ 01.2″ E, 2835 m.

Fun Fact: Did you know that there is a seismic station near the south pole, and that it has been operating since 1957?

Prokofiev and Astronomy

I recently completed teaching a six-week course on the Ukraine-born Russian/Soviet composer Sergei Prokofiev (1891-1953), a course I am eager to reprise in the not-too-distant future. His story is by turns both fascinating and tragic, and he wrote a lot of great music—much of it seldom performed. I am amazed that no one has yet produced an English-language documentary on Prokofiev, nor even a biopic.

Since my primary interests are classical music and astronomy, I am naturally curious about significant classical composers who were also interested in astronomy. Prokofiev was one of those composers.

Prokofiev kept fascinating and extensive diaries between 1907 and 1933, a practice which sadly ceased as soon as he began seriously contemplating a return to the Soviet Union and the increasingly repressive regime of Joseph Stalin.

Here are Prokofiev’s astronomy-related entries from those diaries.

The song Prokofiev is referring to here is Two Poems for voice and piano, op. 9, no. 1. The text is a poem by Russian poet Konstantin Balmont (1867-1942). Here is that poem in an English translation:

In this first performance, Anna Grigorievna Zherebtsova-Andreyeva was the singer, and Dulov (first name unknown) was the pianist.

Here is a performance of this work by Andrey Slavny (baritone) and Yuri Serov (piano), recorded at St. Catherine Lutheran Church in St. Petersburg in 1995.

The astronomy book Prokofiev was referring to is The World of the Heavens [Nebesny Mir], An Illustrated Astronomy for the General Reader by E. I. Ignatiev, published in St. Petersburg in 1916. Hardly a “little book” at over 400 pages!

When Prokofiev writes “the green and white diamond of Sirius” he must be referring to the impressive scintillation of Sirius, the brightest star in the night sky, since at the latitude (50° N) of Kharkiv, Ukraine, where he was at the time, Sirius never reaches an altitude higher than 23° above the horizon.

What’s an arshin, you might be wondering? An arshin is an antiquated Russian unit of length equal to 71.12 cm, so “two arshins” would be a little less than 5 ft. in length.

An editorial footnote indicates that “Presumably, Prokofiev’s Fraunhofer was looted or destroyed in the Petrograd flat after his departure in 1918. It would be worth a fortune today.”

Prokofiev continues,

Prokofiev again continues,

An editorial footnote indicates that “The White Nights in St. Petersburg are normally regarded as lasting from 11 June to 2 July. During this period the sun does not descend far enough below the horizon for the sky to become dark.”

Now on holiday on the Kama river, a tributary of the Volga, Prokofiev writes,

Prokofiev would only have been able to see four satellites of Jupiter with his telescope: Io, Europa, Ganymede, and Callisto. The other two “satellites” must have been background stars. If I have figured correctly, Prokofiev would have been observing Jupiter early morning on Friday, August 24, 1917 (New Style date) which would have been Friday, August 11 (Old Style date) in Russia at that time. The two stars he thought were satellites of Jupiter were probably 8th-magnitude stars HD 28990 and HD 28966.

Prokofiev’s reference to the Sun “belonging” to Hercules indicates he knew about the solar apex, the direction the Sun travels relative to the local standard of rest. William Herschel was the first to demonstrate that the solar apex is in the constellation Hercules.

Balmont refers to the aforementioned poet, Konstantin Balmont.

Prokofiev is referring to the 1917 Russian Constituent Assembly election during the Russian Revolution, and that he observed Venus, Jupiter, Sirius, and the Moon at Kislovodsk.

On his way to his first visit to the United States, Prokofiev is spending some time in Japan. At this time he is in Yokohama. At latitude 35° N, he is indeed getting a good view of Scorpius. The date in brackets is the New Style (Gregorian calendar) date, whereas the non-bracket date is the Old Style (Julian calendar) date.

Prokofiev is now sailing from Yokohama to San Francisco, by way of Honolulu.

Prokofiev is now in New York City.

Prokofiev is, of course, referring to the Royal Observatory, Greenwich, London, England.

This takes place in Paris, and B. N. is Boris Nikolayevich Bashkirov, a wealthy amateur poet and friend of Prokofiev whose pseudonym was Boris Verin. “Linette” is Lina Codina, who would become Prokofiev’s wife in two years’ time.

An editorial footnote states, “When staying in Les Rochelets in the summer of 1921 Prokofiev every evening read aloud a chapter of H. G. Wells’s The Outline of History to his mother and Boris Bashkirov.”

Interesting that this insightful essay was penned on “Pi Day”, since the transcendental π = 3.1415926535897932384626433832795… has infinitely many digits that neither terminate nor enter a permanently repeating pattern.

My take after reading this is that there may be two realities. One reality (our reality) consist of entities that exist within time and space. But there is another reality, where there are entities that exist outside of time and space (of which eternity and infinity are proxies).

As for immortality, since I have no consciousness of anything before I was born, why should I expect that I would have any consciousness of anything after I die? To me, that is the most tragic fact of human existence. Within a few minutes (or hours, if extraordinary measures are taken) after death occurs, all of our knowledge and experience—our memories—are irretrievably lost, and all that remains of us is what we have left behind (writing, music, art, etc.), and the memories of those who are still living who knew us. After all the people who knew us personally have died, then all that remains of our existence are artifacts. And, eventually, all of those will be gone, too. This truly emphasizes the importance of this life, of this world, of this time. How we live our lives and treat others today, tomorrow, and the next day are of paramount importance. It is all we have, or will ever have.

Fatou refers to Pierre Joseph Louis Fatou (1878-1929), mathematician and astronomer. I am virtually certain that “Jacobi” is actually the French astronomer Michel Giacobini (1873–1938).

Here are my observing notes about Gamma Leonis:

Algieba.  Very bright, close double.  Primary is orangish-yellow (2.6 K1-IIIbCN-0.5) and secondary is yellow (3.8 G7IIICN-1).  Relative color seems to change as you watch. 

I think it only fitting to end these excerpts from Prokofiev’s diaries with some of his music. In preparing my Prokofiev course, I came across some noteworthy compositions that were not known to me previously. Most unfortunately, some of these works are almost unknown and seldom played because they were written (under duress, without a doubt) as propaganda pieces. Here is, I believe, his most inspired composition written under such circumstances. It is a cantata for chorus and orchestra that Prokofiev wrote in 1939, called Zdravitsa (literally “A Toast!”), op. 85. It was written to commemorate the 60th birthday of Joseph Stalin. The words are hagiolatry in praise of Stalin (Prokofiev did not write them), but the music is truly divine. Here are three excerpts from a recording by the Russian State Symphony Orchestra and the Russian State Symphonic Cappella, conducted by Valeri Polyansky.

The first excerpt is of the orchestra alone:

Now, choir and orchestra:

And, finally, the glorious finale:

I look forward to the time when Russia will be free from tyranny, and when this gorgeous piece by Sergei Prokofiev gets a new libretto. No longer a toast to the despot Stalin, but a toast to peace-loving people throughout the world!

Prokofiev, S. (2006). Diaries 1907-1914: Prodigious youth (A. Phillips, Ed.). Faber & Faber.

Prokofiev, S. (2008). Sergey Prokofiev: Diaries 1915-1923: Behind the mask (A. Phillips, Ed.). Faber & Faber.

Prokofiev, Sergei. (2012). Sergey Prokofiev diaries 1924-1933: Prodigal son. Faber & Faber.

TYC 5134-1820-1: A New Double Star Discovery

Shadow path of TYC 5134-01820-1 occulted by asteroid 1330 Spiridonia – June 26, 2023 UT

On 26 June 2023 UT, Vince Sempronio near Benson, Arizona and David Oesper near Tucson, Arizona observed an occultation of the 12.2-magnitude* star Tycho 5134-1820-1 in the constellation Aquila by the 15.1-magnitude asteroid 1330 Spiridonia. The predicted magnitude drop should have been around 2.9 magnitudes (15.1m-12.2m) by both observers, but I observed only about a 0.2-magnitude drop, and Vince a 1.5 magnitude-drop. After expert analysis by David Gault and David Herald in Australia, it was determined that we had discovered a new double star!

Observer locations for the June 26, 2023 occultation event

Fortuitously, Vince had observed 1330 Spiridonia covering up only the primary (brightest) component, and I had observed 1330 Spiridonia covering up only the secondary component. Both of us made our observations with 8-inch telescopes.

Vince Sempronio’s light curve (11.2 seconds, 70 data points)
David Oesper’s light curve (60.7 seconds, 455 data points)

The double star solution from our observations gives the following:

G magnitude of the primary component: 12.4

G magnitude of the secondary component: 13.9

Separation: 59.7 milliarcseconds (0.0597 arcseconds)

Position Angle: 141.8° (eastward from north)

The double star solution

Follow up observations over time will be needed to determine whether this is an optical double (chance alignment) or a true binary system. The distance to TYC 5134-1820-1 is currently estimated to be between 2,689 and 2,883 light years (SIMBAD). Definitely not in the neighborhood.

Even though double stars are common in our galaxy (and everywhere else in the universe), and understanding that our observations represent only the tiniest contribution to scientific knowledge, there is satisfaction in knowing that we discovered something not known by anyone else before. Besides, you never know when a discovery such as this will draw attention to an unusual and astrophysically-interesting system.

In conclusion, here is but one example showing that observations of stellar occultations by the minor planets of our solar system presents an exquisite method of discovering very close double (and possibly binary) stars, not assayable by any other technique.

*Gaia G magnitude

Does 790 Pretoria Have a Moon?

On 14 Dec 2023 at 10:17:12.943 UT, the 13.6-magnitude outer main belt asteroid 790 Pretoria was in the middle of covering up the 10.9-magnitude star TYC 1299-730-1 (UCAC4 532-018101) in the constellation Taurus, as seen from my vantage point on the west side of Tucson, Arizona.

Stellar Occultation of TYC 1299-730-1 by 790 Pretoria

I observed a 6.6-second occultation, but noticed a single-point event with the same magnitude drop as the main occultation, but 0.5 second earlier. A close up of that section of the light curve is shown below.

Stellar Occultation of TYC 1299-730-1 by 790 Pretoria showing possible moonlet

If 790 Pretoria has a moon that also occulted the star, then you would expect the magnitude drop when the star is covered up to be the same—the magnitude of the asteroid (and its satellite) alone. This is indeed the case here.

An analysis of all the data points prior to these two occultation events indicates that there is only a 1/130,000 chance that the single-point dip was caused by noise. The time-resolution of each data point is 0.03 seconds, so it seems likely that the moonlet occultation event was very close to 0.03 seconds in duration, as the data points on either side fall comfortably within the baseline.

Originally, there were four other observers signed up for this event (three in Arizona and two in Texas), but the other two Arizona observers were not able to observe and the two Texas observers were clouded out, leaving only me with my 8-inch Meade LX90 telescope on the back patio of my home to observe the event.

No moon of 790 Pretoria has yet been reported, and since no one else observed the 14 Dec 2023 event, my observation can only serve as a suggestion that 790 Pretoria might have a moon, but not proof.

Prior to my observation there were 14 stellar occultation events of 790 Pretoria observed, the first in 1998 and the last in 2021. We don’t yet have a shape model for 790 Pretoria.

Only three light curves from previous 790 Pretoria occultation events are available through the VizieR archive. These are listed and shown below.

VizieR Light Curves of previous stellar occultations by 790 Pretoria
LC 238 by R. Sandy
LC 7658 by Dean Hooper
LC 7939 by S. Messner

Here is a list of all previous occultation chords for 790 Pretoria.

And details of the North American events, including the 14 Dec 2023 event I observed.

The 19 Jul 2009 event resulted in the discovery that TYC 2255-01354-1 is a double star.

Superheavy Elements

There are currently 118 known chemical elements. The most recent, 118 Oganesson (chemical symbol Og), was first synthesized in 2002 . Its only known isotope, \mathbf{\frac{294}{118}\textrm{\textbf{Og}}} (118 protons + 176 neutrons = 294 nucleons), has a half-life of just 0.0007 seconds, and to date only five oganesson atoms have been produced.

It is possible, given our current knowledge of nuclear physics, that there is at least one island of nuclear stability where stable or quasi-stable isotopes of superheavy elements exist. One such island might exist around Z = 164, that is an element having 164 protons and something like 246 neutrons.

Are any superheavy elements stable enough to be found in nature? Is there any astrophysical process that could produce them? If superheavy elements exist, we would expect such matter to have a mass density in excess of the densest-known stable element, osmium (element 76), 22.59 g/cm3. Superheavy elements around Z = 164 are expected to have a mass density between 36.0 and 68.4 g/cm3.

Researchers at the University of Arizona in Tucson explain that superheavy elements might exist in nature, either in the exotic form of extremely dense alpha matter — nuclear matter composed of alpha particles in a Bose-Einstein condensate-like configuration — or as standard matter. Though a long shot, they suggest looking at asteroids (and other objects) possibly having anomalously high densities, which they call Compact Ultradense Objects (CUDOs).

In order to calculate the density of an asteroid, you need to measure its volume and its mass. The volume can be calculated if you know the size and shape of the asteroid, and the mass can best be calculated if the asteroid has a satellite (either natural or artificial), or from a spacecraft flyby. A less certain mass can be calculated by measuring how an asteroid gravitationally perturbs a neighboring asteroid as they both orbit around the Sun. We must keep in mind that any asteroids that presently appear to have an unusually high density may later be found to have a more normal density upon better estimates of the size and shape of the asteroid, and especially its mass.

The most recent available table of asteroid bulk densities can be found on the SiMDA (Size, Mass, and Density of Asteroids) web site. In that table, a bulk density accuracy rank of A (most accurate) to E (least accurate), and X (unrealistic) for each object is given. Among the A-rank densities, we find that 16 Psyche is listed as having the highest bulk density of 3.90 ± 0.29 g/cm3. NASA’s Psyche robotic spacecraft was launched on October 13, 2023 and is expected to begin orbiting 16 Psyche in August 2029.

Among the B-rank densities, two asteroids have nominal bulk densities higher than 16 Psyche’s: 135 Hertha at 4.45 ± 0.63 g/cm3 and 192 Nausikaa at 4.10 ± 0.70 g/cm3.

Among the C-rank densities, 21 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "C" Asteroid Densities (> 16 Psyche)

206 Hersilia 6.08 ± 2.55
181 Eucharis 5.46 ± 2.43
410 Chloris 4.96 ± 2.41
679 Pax 4.95 ± 1.45
110 Lydia 4.88 ± 1.75
97 Klotho 4.80 ± 1.01
124 Alkeste 4.74 ± 2.22
275 Sapientia 4.69 ± 1.12
92 Undina 4.64 ± 1.75
34 Circe 4.63 ± 1.21
56 Melete 4.57 ± 1.07
102 Miriam 4.46 ± 1.88
680 Genoveva 4.37 ± 2.06
129 Antigone 4.35 ± 2.14
69 Hesperia 4.33 ± 1.11
709 Fringilla 4.12 ± 1.98
89 Julia 4.01 ± 1.61
675 Ludmilla 3.99 ± 1.94
201 Penelope 3.99 ± 1.97
455 Bruchsalia 3.93 ± 1.29
354 Eleonora 3.93 ± 1.84

Among the D-rank densities, 16 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "D" Asteroid Densities (> 16 Psyche)

250 Bettina 7.84 ± 5.42
138 Tolosa 7.69 ± 4.39
360 Carlova 6.62 ± 4.51
388 Charybdis 5.80 ± 3.66
43 Ariadne 5.54 ± 2.84
536 Merapi 5.39 ± 4.77
172 Baucis 5.34 ± 3.31
420 Bertholda 4.94 ± 4.44
103 Hera 4.78 ± 2.87
491 Carina 4.58 ± 3.11
683 Lanzia 4.49 ± 2.69
849 Ara 4.29 ± 2.18
506 Marion 4.16 ± 2.29
363 Padua 4.10 ± 2.25
705 Erminia 4.02 ± 2.39
786 Bredichina 3.91 ± 2.28

Among the E-rank densities, 7 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "E" Asteroid Densities (> 16 Psyche)

2004 PB108 6.74 ± 7.23
1013 Tombecka 6.39 ± 53.43
306 Unitas 6.23 ± 6.77
132 Aethra 5.09 ± 7.72
445 Edna 4.60 ± 4.91
147 Protogeneia 4.18 ± 5.03
769 Tatjana 4.09 ± 4.38

Among the X-rank densities, 14 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "X" Asteroid Densities (> 16 Psyche)

1686 De Sitter 430.61 ± 213.19
33 Polyhymnia 75.32 ± 9.72
1428 Mombasa 43.03 ± 14.78
152 Atala 42.29 ± 10.80
949 Hel 12.31 ± 5.14
582 Olympia 9.98 ± 27.31
61 Danae 9.74 ± 9.45
665 Sabine 9.05 ± 5.19
217 Eudora 8.94 ± 0.64
204 Kallisto 8.89 ± 26.79
234 Barbara 8.89 ± 29.30
202 Chryseis 8.66 ± 1.63
126 Velleda 8.64 ± 106.21
67 Asia 8.59 ± 1.23

Obviously, most—if not all—of the asteroids listed above will eventually be found to have bulk densities less than that of 16 Psyche as more accurate masses and volumes are determined. Presently, only the following asteroids have minimum bulk densities greater than that of 16 Psyche, assuming the mean error listed is correct:

Asteroid Densities > 16 Psyche (within error)

1686 De Sitter 430.61 ± 213.19
33 Polyhymnia 75.32 ± 9.72
1428 Mombasa 43.03 ± 14.78
152 Atala 42.29 ± 10.80
949 Hel 12.31 ± 5.14
217 Eudora 8.94 ± 0.64
202 Chryseis 8.66 ± 1.63
67 Asia 8.59 ± 1.23

LaForge, Price, and Rafelski choose 33 Polyhymnia as the current best candidate to search for superheavy elements. Even a small amount of superheavy elements (especially in the alpha matter state) could significantly raise the bulk density of the asteroid as a whole. Kretlow lists the mass of 33 Polyhymnia as (6.20 ± 0.74) × 1018 kg and its volume-equivalent diameter as 54.0 ± 0.9 km, giving a bulk density around 75 g/cm3.

This finding is not without controversy, however. See the following discussion:

Kretlow, M. Size, Mass and Density of Asteroids (SiMDA) – A Web Based Archive and Data Service” (2020).

LaForge, E., Price, W. & Rafelski, J. Superheavy elements and ultradense matter. Eur. Phys. J. Plus 138, 812 (2023).

Limb Darkening and Luminosity

The Sun photographed on 8 May 2019 in white light by Matúš Motlo
showing sunspots, faculae, and limb darkening

The photosphere of our Sun and most other stars exhibit a phenomenon called limb darkening where the disk is brighter at the center than at the edges at optical wavelengths. This effect is more pronounced towards the violet end of the visible spectrum than it is towards the red end.

Limb darkening occurs because there is a strong temperature gradient within the photosphere (deeper is hotter) and we see deeper into the Sun at the center of the disk then we do toward the edges. The deeper, hotter regions of the photosphere produce more visible light than do the shallower, cooler regions.

Does this non-uniformity of light emitted from the disk of a star mean we are “missing” some light in measuring a star’s brightness that would then affect our ability to accurately calculate the star’s total luminosity? Not at all. Here’s why.

Stars are almost always isotropic emitters of light. That means they emit light uniformly in all directions. At a given distance from the star, an observer would measure the same brightness of the star no matter what their direction from it. Even though the edges of the stellar disk are darker, the center is brighter, and the total integrated brightness is the same as it would be if all parts of the disk were emitting uniformly.

We calculate the luminosity of the star by measuring the amount of light we receive across our collecting area (whether that be the human eye or the telescope aperture), and then dividing this collecting area into the total surface area of a sphere centered on the star and having a radius that is our distance from the star. We then take that quotient times the amount of light we detect in our small collecting area to get the total amount of light emitted by the star in all directions.

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.

Otto Struve & Exoplanets, 1952

It’s too bad the remarkable Russian-born American astronomer Otto Struve (1897-1963) never lived to see the discovery of the first exoplanets, especially considering how he was probably the first to suggest the two main techniques by which they are now discovered.

The first discovery of something that could be called an exoplanet was announced in 1992 by the Polish astronomer Aleksander Wolszczan (1946-) and Canadian astronomer Dale Frail (1961-). They found two planets orbiting a neutron star 2,300 light years away in the constellation Virgo. This neutron star is the pulsar PSR 1257+12, which had only recently been discovered by Wolszczan (1990). The pulsar planets were detected using a variant of the Doppler (radial velocity) method, and a third planet was discovered by the same team in 1994. These planets likely formed from the debris disk formed when two white dwarf stars merged, so they could be considered “exotic” planets, quite unlike anything found in our solar system.

In 1995, the first exoplanet orbiting a “normal” star was announced by Swiss astronomers Michel Mayor (1942-) and Didier Queloz (1966-). Using the Doppler (radial velocity) method, they found a “hot Jupiter” orbiting the star 51 Pegasi at a distance of 51 light years (nice coincidence!).

In 1999, independent teams led by Canadian-American astronomer David Charbonneau (1974-) and American astronomer Gregory W. Henry (1972-) were the first to use the transit method to detect an exoplanet. They confirmed a hot Jupiter orbiting the star HD 209458 (also in Pegasus, another nice coincidence) 157 light years distant that had been discovered using the Doppler (radial velocity) technique only weeks earlier.

As you can see, the 1990s was the decade when exoplanetary science got its start!

Getting back to the prescience of Otto Struve—40 years prior to the discovery of the first exoplanets—Joshua Winn (1972-) in his newly-published The Little Book of Exoplanets writes:

Although the discovery of hot Jupiters came as a surprise, it’s not quite true that nobody foresaw them. In 1952, Otto Struve, an astronomer at the University of California at Berkeley, published a short paper pointing out that the precision of Doppler measurements had become good enough to detect planets—but only if there existed planets at least as massive as Jupiter with orbital periods as short as a few days. Setting aside the question of how such a planet might have formed, he realized there is no law of physics that forbids such planets from existing. In an alternate history, Struve’s paper inspired astronomers to launch a thousand ships and explore nearby stars for hot Jupiters. In fact, his paper languished in obscurity. None of the pioneers—neither Walker, Latham, Mayor, nor Queloz—were influenced by Struve’s paper. The planet around 51 Pegasi probably could have been discovered in the early 1960s, or surely by Walker in the 1980s, had the Telescope Time Allocation Committee allowed him to observe a larger number of stars.

Here is Otto Struve’s 1952 paper in its entirety (references omitted), published in the October 1952 issue of The Observatory.


By Otto Struve

With the completion of the great radial-velocity programmes of the major observatories, the impression seems to have gained ground that the measurement of Doppler displacements in stellar spectra is less important at the present time than it was prior to the completion of R. E. Wilson’s new radial-velocity catalogue.

I believe that this impression is incorrect, and I should like to support my contention by presenting a proposal for the solution of a characteristic astrophysical problem.

One of the burning questions of astronomy deals with the frequency of planet-like bodies in the galaxy which belong to stars other than the Sun. K. A. Strand’s discovery of a planet-like companion in the system of 61 Cygni, which was recently confirmed by A. N. Deitch at Poulkovo, and similar results announced for other stars by P. Van de Kamp and D. Reuyl and E. Holmberg have stimulated interest in this problem. I have suggested elsewhere that the absence of rapid axial rotation in all normal solar-type stars (the only rapidly-rotating G and K stars are either W Ursae Majoris binaries or T Tauri nebular variables, or they possess peculiar spectra) suggests that these stars have somehow converted their angular momentum of axial rotation into angular momentum of orbital motion of planets. Hence, there may be many objects of planet-like character in the galaxy.

But how should we proceed to detect them? The method of direct photography used by Strand is, of course, excellent for nearby binary systems, but it is quite limited in scope. There seems to be at present no way to discover objects of the mass and size of Jupiter; nor is there much hope that we could discover objects ten times as large in mass as Jupiter, if they are at distances of one or more astronomical units from their parent stars.

But there seems to be no compelling reason why the hypothetical stellar planets should not, in some instances, be much closer to their parent stars than is the case in the solar system. It would be of interest to test whether there are any such objects.

We know that stellar companions can exist at very small distances. It is not unreasonable that a planet might exist at a distance of 1/50 astronomical unit, or about 3,000,000 km. Its period around a star of solar mass would then be about 1 day.

We can write Kepler’s third law in the form V^{3} \sim \frac{1}{P}. Since the orbital velocity of the Earth is 30 km/sec, our hypothetical planet would have a velocity of roughly 200 km/sec. If the mass of this planet were equal to that of Jupiter, it would cause the observed radial velocity of the parent star to oscillate with a range of ± 0.2 km/sec—a quantity that might be just detectable with the most powerful Coudé spectrographs in existence. A planet ten times the mass of Jupiter would be very easy to detect, since it would cause the observed radial velocity of the star to oscillate with ± 2 km/sec. This is correct only for those orbits whose inclinations are 90°. But even for more moderate inclinations it should be possible, without much difficulty, to discover planets of 10 times the mass of Jupiter by the Doppler effect.

There would, of course, also be eclipses. Assuming that the mean density of the planet is five times that of the star (which may be optimistic for such a large planet) the projected eclipsed area is about 1/50th of that of the star, and the loss of light in stellar magnitudes is about 0.02. This, too, should be ascertainable by modern photoelectric methods, though the spectrographic test would probably be more accurate. The advantage of the photometric procedure would be its fainter limiting magnitude compared to that of the high-dispersion spectrographic technique.

Perhaps one way to attack the problem would be to start the spectrographic search among members of relatively wide visual binary systems, where the radial velocity of the companion can be used as a convenient and reliable standard of velocity, and should help in establishing at once whether one (or both) members are spectroscopic binaries of the type here considered.

Berkeley Astronomical Department, University of California.
1952 July 24.

Most Distant Human-Made Object

In 1895, Italian inventor and electrical engineer Guglielmo Marconi (1874-1937) produced the first human-made radio waves capable of traveling beyond the Earth, so radio evidence of the existence of human civilization has now traveled 128 light years from Earth. Assuming a stellar number density in the solar neighborhood of (7.99 ± 0.11) × 10−2 stars per cubic parsec1, Earth’s radio emissions have already reached about 20,000 star systems.

The most distant physical human-made object, however, is the Voyager 1 spacecraft, now over 160 AU from the solar system barycenter (SSB), a distance of almost 15 billion miles. That certainly sounds impressive by human standards, but that is only 0.0025 light years. As the distance of Voyager 1 from the solar system barycenter is constantly increasing, you’ll want to visit JPL Horizons to get up-to-date information using the settings below for your date range of interest. Delta gives the distance from the SSB to the Voyager 1 spacecraft in astronomical units (AU).

This still-functioning spacecraft that was launched on September 5, 1977, flew by Jupiter on March 5, 1979, and flew by Saturn on November 12, 1980, is now heading into interstellar space in the direction of the constellation Ophiuchus, the Serpent Bearer, near the Ophiuchus/Hercules border.

Given Voyager 1’s current distance (from Earth), a radio signal from Earth traveling at the speed of light would take 22 hours and 8 minutes to reach Voyager 1, and the response from Voyager 1 back to Earth another 22 hours and 8 minutes. So, when engineers send a command to Voyager 1, they won’t know for another 44 hours and 16 minutes (almost 2 days) whether Voyager 1 successfully executed the command. Patience is indeed a virtue!

Thanks to three onboard radioisotope thermoelectric generators (RTGs)2, Voyager 1 should be able to continue to operate in the bone-chilling cold of deep space until at least 2025.

In about 50,000 years, Voyager 1 will be at a distance comparable to the nearest stars.

1The Fifth Catalogue of Nearby Stars (CNS5)
Alex Golovin, Sabine Reffert, Andreas Just, Stefan Jordan, Akash Vani, Hartmut Jahreiß, A&A 670 A19 (2023), DOI: 10.1051/0004-6361/202244250

2At launch, the Voyager 1 RTGs contained a total of about 4.5 kg of plutonium-238, generating 390W of electricity.

The Dimmest Constellation

You are probably familiar with at least the names of the twelve constellations of the zodiac:


But are you familiar with the twelve constellations that have no stars brighter than 4th magnitude?

Coma Berenices
Corona Australis

All but two of these dim constellations are, at least in part, visible from southern Arizona; Chamaeleon and Mensa require a trip south to see.

The southern constellation Mensa, the Table Mountain (declination -70° to -85°) is a ghost of a constellation, exhibiting no star brighter than magnitude 5.1. That’s 17 times fainter than Polaris! In fact, that’s fainter than all the stars of the Little Dipper asterism! Mensa does have one claim to fame, however. The Large Magellanic Cloud, satellite galaxy of our Milky Way galaxy, straddles most of the border that Mensa shares with Dorado, the Swordfish.

Mensa is far and away the dimmest constellation. But Mensa is a small constellation, bested in size by 74 of the 88 constellations. So perhaps it is not too surprising that a small constellation is less likely to harbor a bright star. Another measure of faint, perhaps, is to determine which of these twelve constellations with no star brighter than 4th magnitude is largest. That might be more remarkable, because one is less likely to find no bright stars in a large area of sky than in a small area of sky. By this measure, Camelopardalis, the Giraffe, wins without a doubt. Camelopardalis is the 18th largest constellation, and yet contains no star brighter than magnitude 4.0. It is that empty region you might have not noticed midway between Capella and Polaris, best viewed at evening twilight’s end during the month of February each year.