On Sunday afternoon, October 13, 2024, I attended a wonderful concert by the Southern Arizona Symphony Orchestra (SASO) that included a rousing performance of Scheherazade by the Russian composer Nikolai Rimsky-Korsakov.
Early that evening, I was the first person in the world to observe the composer’s namesake asteroid 4534 Rimskij-Korsakov passing in front of a distant star and, briefly, blocking its light. As a classical music lover, that made me very happy.
The 0.5-second occultation of the 13.6-magnitude star UCAC4 558-003434 by the asteroid 4534 Rimskij-Korsakov on 14 Oct 2024 2:23:46 UT as seen from Tucson, Arizona using an 8-inch telescope
4534 Rimskij-Korsakov was discovered on 6 Aug 1986 by the Russian astronomer Nikolai Chernykh (1931-2004) at the Crimean Astrophysical Observatory near the small settlement of Nauchnyi on the Crimean peninsula, part of Ukraine but illegally occupied by Putin’s Russian forces since 2014.
At the time of its discovery, this asteroid received its preliminary designation 1986 PV4. As is the custom, the discoverer gets to choose a name for the asteroid if they so desire, and Nikolai Chernykh decided to name his discovery after Nikolai Rimsky-Korsakov (1844-1908). This name was approved by the IAU and published in Minor Planet Circular 23352 on 25 Apr 1994.
4534 Rimskij-Korsakov is not a large asteroid. Its average diameter is estimated to be just 9.9 miles. Had I been right on the centerline of the asteroid’s shadow, I should have seen the star disappear for about 1.2 seconds. Given that I had to use an integration time of 0.27s due the faintness of the occulted star, the 0.5-second event I recorded had only two data points in the “dip” where the 13.6 magnitude star disappeared leaving only the sky background since the asteroid’s estimated magnitude was just 17.5m. Normally, one likes to have at least three data points in the dip, but two is better than one and the event happened at exactly the predicted time.
Nikolai Rimsky-Korsakov wrote a lot of great music, and he was a master of orchestration and orchestral “colors”. Here are my favorite works. If you don’t already know them, give them a listen!
Capriccio espagnol
Le Coq d’Or, Suite [arranged by Alexander Glazunov (1865-1936) & Maximilian Steinberg (1883-1946)]
There are currently 118 known chemical elements. The most recent, 118 Oganesson (chemical symbol Og), was first synthesized in 2002 . Its only known isotope, (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:
References Kretlow, M. Size, Mass and Density of Asteroids (SiMDA) – A Web Based Archive and Data Service” (2020). https://astro.kretlow.de/?SiMDA
LaForge, E., Price, W. & Rafelski, J. Superheavy elements and ultradense matter. Eur. Phys. J. Plus138, 812 (2023). https://arxiv.org/abs/2306.11989 https://doi.org/10.1140/epjp/s13360-023-04454-8
157 asteroids have orbits that lie entirely within Earth’s aphelion distance from the Sun (1.016710 AU). That number reduces to 54 inside Earth’s semimajor axis distance (1.000001 AU). That number further reduces to 28 inside Earth’s perihelion distance (0.983292 AU). Those 28 asteroids are listed below.
Only one asteroid lies entirely within Venus’s orbit, 594913 ‘Ayló’chaxnim (2020 AV2)1, and none are known inside Mercury’s orbit…so far. Asteroids inside of the Earth’s orbit are extremely difficult to detect since their angular distance from the Sun is never very large, and the glare of the Sun interferes. This is especially true for any asteroids that might exist inside of Mercury’s orbit.
An asteroid is given a provisional designation when it is discovered that begins with the year of discovery. After the orbit of the asteroid has been sufficiently well-determined, it is given a number. Then, eventually, the numbered asteroid is given a name.
Only 8 of the 28 asteroids entirely within Earth’s perihelion distance have received numbers, and only two of these have been given a name: ‘Ayló’chaxnim and Atira.
Interestingly, half of these 28 asteroids have been discovered since 2017, including 1 so far this year. The first was discovered in 1998.
In the table below, i is the orbital inclination relative to the ecliptic plane, e is the orbital eccentricity, q is the perihelion distance, a is the semimajor axis distance, Q is the aphelion distance, and P is the orbital period. The table is listed in order of aphelion distance, smallest to largest.
Asteroids with orbits that lie entirely within Earth’s perihelion distance from the Sun
Italian monk, mathematician, and astronomer Giuseppe Piazzi (1746-1826) discovered an unexpected 8th magnitude object in Taurus near Mars and the Pleiades at around 8:00 p.m. on January 1, 1801 at his observatory in Palermo, Sicily. Thinking it a comet, he recorded the position of the object over several nights, until illness forced him to quit on February 11, just a few days after the object passed fairly close to Mars. By early May, the object was too close to the Sun in the western sky to observe, and Piazzi despaired of ever recovering the object. The now-famous 24-year-old German mathematician Carl Gauss (1777-1855) came to the rescue. Gauss used Piazzi’s positions to determine an orbit for Ceres (so named by Piazzi) and predicted from the scant data its future positions when it would once again be visible in the night sky. Ceres was recovered only a half-degree away from its predicted position by Hungarian astronomer Franz Xaver von Zach (1754-1832) on December 7, close to Denebola and not far from a close conjunction of the planets Jupiter and Saturn, and then confirmed after a long stretch of cloudy weather on December 31, 1801. The German amateur astronomer Heinrich Olbers (1758-1840) found Ceres at Bremen two days later on January 2, 1802. Olbers (of Olbers’ Paradox fame) discovered the second asteroid, Pallas, on March 28, 1802. Many, many more asteroids have been discovered since then. They are sequentially numbered, originally in order of their discovery date, but nowadays in order of their receiving a precise orbit determination.
Fast forward.
The names of asteroids 998 through 1002, discovered between August
6-15, 1923, have special significance.
998 Bodea – named in honor of German astronomer Johann Elert Bode (1747-1826), whose empirical relationship of the distances of the planets (Titius-Bode Law) indicated that there should be a planet between the orbits of Mars and Jupiter, touching off a massive search led by von Zach for a new planet.
999 Zachia – named in honor of Franz Xaver von Zach, who
published Piazzi’s observations and recovered Ceres after Gauss’
predicted positions.
1000 Piazzia – named in honor of Giuseppe Piazzi, who
discovered the first asteroid, 1 Ceres.
1001 Gaussia – named in honor of Carl Friedrich Gauss, who
predicted the position of Ceres so it could be recovered.
1002 Olbersia – named in honor of Heinrich Olbers who was the second person to recover Ceres and the discoverer of the second asteroid, 2 Pallas (and 4 Vesta, by the way).
Fortunately, German astronomer Johann Daniel Titius (1729-1796) finally did get an asteroid named after him as well: 1998 Titius, discovered on February 24, 1938.
As of August 19, 2019, 796,422 minor planets (asteroids, trans-Neptunian objects, etc., but not including comets) have been discovered, but only 541,128 have orbits that are well-enough determined that they have been given a minor planet number. When a minor planet is first discovered, it is given a provisional designation based on the date of discovery. For example, 2019 PE3 was discovered during the first half of August 2019. After enough high-quality astrometric data has been collected to determine an accurate orbit, the minor planet is assigned a number. For example, minor planet 1996 TB1 was discovered by IOTA member George Viscome on October 5, 1996. It received a number, 35283, in 2000, and it received a name, Bradtimerson, earlier this year (2019). George submitted the name to the IAU after Brad Timerson, mentor and inspiration to many of the current crop of asteroid occultation observers, passed away on October 17, 2018. So we now have 35283 Bradtimerson.
The counts in the paragraph above show us that 67.9% of the minor planets that have been discovered have been assigned a number. Of these, only 21,922 (4.1%) have received a name.
Many asteroids have been given interesting or unusual names. Excluding the many fine individuals (real, not fictional) who have an asteroid named after them, here are a few of my favorites. There are a few here that are actually named after a person, but the minor planet name has a meaning beyond just the person’s name.
Remember, these are real places that will be visited someday. Oh, to be so lucky!
Lots of asteroids are awaiting names. Can you come up with some interesting, entertaining, or poetic ones? Give it a try, check this list or do a search here to make sure it is new, and then post a comment here and I’ll probably include your ideas in this article, giving you credit, of course. Be creative!
To get you in the spirit, here are a few names I’ve come up with:
Botanica
Distantia
Eternium
Gandalf
Hello & Goodbye [consecutive numbers, in celebration of The Beatles song written by Paul McCartney]
Of the 793,918 asteroids and trans-Neptunian objects (TNOs) currently catalogued, only 98 are in retrograde orbits around the Sun. That’s just 0.01%.
By “retrograde” we mean that the object orbits the Sun in the opposite sense of all the major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. From a vantage point above the north pole of the Earth, all of the major planets orbit in a counterclockwise direction around the Sun.
But a retrograde object would be seen to orbit in a clockwise direction around the Sun, as is shown in the animation below for Jupiter retrograde co-orbital asteroid 514107 (2015 BZ509), with respect to Jupiter and its two “clouds” of trojan asteroids.
Of these 98 retrograde objects, only 14 have orbits well-enough determined to have received a minor planet number, and only one has yet received an official name (20461 Dioretsa).
Semimajor Axis (a) between…
Number of Retrograde Minor Planets
Mars – Jupiter
3
Jupiter – Saturn*
20
Saturn – Uranus*
15
Uranus – Neptune*
20
TNOs
40
*asteroids between the orbits of Jupiter and Neptune are often referred to as centaurs
At least some of these objects may be captured interstellar objects.
Let’s now take a look at some of these 98 retrograde objects in greater detail.
20461 Dioretsa The first retrograde asteroid to be discovered was 20461 Dioretsa, in 1999. The only named retrograde asteroid to date, Dioretsa is an anadrome of the word “asteroid”. It is a centaur in a highly eccentric orbit (0.90), ranging between the orbits of Mars and Jupiter out to beyond the orbit of Neptune. Objects in cometlike orbits that show no evidence of cometary activity are often referred to as damocloids. Dioretsa is both a centaur and a damocloid. Its orbital inclination (relative to the ecliptic) is 160°, which is a 20° tilt from an anti-ecliptic orbit. It takes nearly 117 years to orbit the Sun once. It is a dark object with a reflectivity only around 3% and is estimated to be about 9 miles across.
2010 EQ169 This retrograde asteroid holds the distinction (at least temporarily) of being the most highly-inclined main-belt asteroid (91.6°), relative to the ecliptic plane. It is also the retrograde asteroid with the smallest semimajor axis (2.05 AU) and lowest orbital eccentricity (0.10). Unfortunately, it was discovered after the fact by analyzing past data from the Wide-field Infrared Survey Explorer (WISE) space telescope, and has not been seen since. We have only a three-day arc of 17 astrometric observations of 2010 EQ169 between March 7-9, 2010 from which to determine its orbit. Nominally, 2010 EQ169 orbits the Sun at nearly a right angle to the ecliptic plane once every 2.9 years, between the orbits of Mars and Jupiter. However, our knowledge of its orbit is extremely uncertain, as shown below, and it has been lost. Our only hope will be to back-calculate the positions of future asteroids discovered to these dates to see if it matches the WISE positions.
Element
Value
1σ Uncertainty
Inclination (i)
91.606°
18.177°
Semimajor Axis (a)
2.0518 AU
2.2176
Orbital Eccentricity (e)
0.10153
0.90213
Orbital Period (P)
2.94y
4.765
2013 BL76 This retrograde TNO has the largest known semi-major axis of any of the retrograde non-cometary objects: 966.4274 ± 2.2149 AU. In a highly eccentric cometlike orbit (e = 0.99135), its perihelion is in the realm of the centaurs between the orbits of Jupiter and Saturn (8.35 AU), and its aphelion is way out around 1,924 AU. It takes about 30,000 years to orbit the Sun. Its orbit is inclined 98.6° with respect to the ecliptic.
2013 LA2 This retrograde centaur is in an orbit closest to the ecliptic plane (i = 175.2°), tilted 4.8° with respect to the ecliptic. It orbits the Sun about once every 21 years between the orbits of Mars and Uranus.
2017 UX51 The distinction for this retrograde TNO is that it has the highest orbital eccentricity of any non-cometary solar system object (e = 0.9967). Or is it an old inactive comet? 2017 UX51 orbits the Sun every 7,419 ± 2,883 years as close in as between the orbits of Earth and Mars (perihelion q = 1.24 AU)—classifying it as an Amor object—out to far beyond the orbit of Neptune (aphelion Q = 759.54 ± 196.77 AU). Its orbital inclination is 108.2°.
343158 (2009 HC82) An Apollo asteroid, 343158 is the only known retrograde near-Earth asteroid (NEA), with an orbital inclination of 154.4°. It orbits the Sun every 4.0 years, between 0.49 AU (almost as close in as the aphelion of Mercury) out to 4.57 AU (between the orbits of Mars and Jupiter).
References Conover, E., 2017. Science News, 191, 9, 5.
Finally, a turnkey system is available for recording stellar occultations by asteroids and trans-Neptunian objects (TNOs)! All you need besides the kit is a telescope and a PC. A big thank you to Ted Blank and IOTA for putting this together!
Occultation Recording Kit
Highly sensitive RunCam Night Eagle Astro Edition video camera
0.5x focal reducer & adapters to attach camera to 1¼-inch eyepiece holder
We need more observers in the Midwest (everywhere, really) to give us more chords across the asteroids and TNOs, thus increasing the scientific value of the observations. Right now, we are desperately in need of observers in Iowa (where I lived for many years and will always be home to me), and we have precious few active observers in Wisconsin (yours truly), Minnesota (Steve Messner), and Illinois (Bob Dunford, Aart Olsen, Randy Trank).
If you have an interest in pursuing this interesting and rewarding speciality that gives you the opportunity to make a valuable scientific contribution, feel free to post a comment here and I’ll be happy to help!
Planetary orbits are randomly oriented throughout our galaxy. The probability that an exoplanet’s orbit will be fortuitously aligned to allow that exoplanet to transit across the face of its parent star depends upon the radius of the star, the radius of the planet, and the distance of the planet from the star. In general, planets orbiting close-in are more likely to be seen transiting their star then planets orbiting further out.
The equation for the probability of observing a exoplanet transit event is
where ptra is the transit probability, R* is the radius of the star, Rp is the radius of the planet, a is the semi-major axis of the planetary orbit, and e is the eccentricity of the planetary orbit
Utilizing the data in the NASA Exoplanet Archive for the 1,463 confirmed exoplanets where the above data is available (and assuming e = 0 when eccentricity is unavailable), we find that the median exoplanet transit probability is 0.0542. This means that, on average, 1 out of every 18 planetary systems will be favorably aligned to allow us to observe transits. However, keep in mind that our present sample of exoplanets is heavily biased towards large exoplanets orbiting close to their parent star. Considering a hypothetical sample of Earth-sized planets orbiting 1 AU from a Sun-sized star, the transit probability drops to 0.00469, which means that we would be able to detect only about 1 out of every 213 Earth-Sun analogs using the transit method.
How might we detect some of the other 99.5%? My admired colleague in England, Abdul Ahad, has written a paper about his intriguing idea: “Detecting Habitable Exoplanets During Asteroidal Occultations”. Abdul’s idea in a nutshell is to image the immediate environment around nearby stars while they are being occulted by asteroids or trans-Neptunian objects (TNOs) in order to detect planets orbiting around them. While there are many challenges (infrequency of observable events, narrow shadow path on the Earth’s surface, necessarily short exposure times, and extremely faint planetary magnitudes), I believe that his idea has merit and will one day soon be used to discover and characterize exoplanets orbiting nearby stars.
Ahad notes that the apparent visual magnitude of any given exoplanet will be directly proportional to the apparent visual magnitude of its parent star, since exoplanets shine by reflected light. Not only that, Earth-sized and Earth-like planets orbiting in the habitable zone of any star would shine by reflected light of the same intrinsic brightness, regardless of the brightness of the parent star. He also notes that the nearer the star is to us, the greater will be a given exoplanet’s angular distance from the occulted star. Thus, given both of these considerations (bright parent star + nearby parent star = increased likelihood of detection), nearby bright stars such as Alpha Centauri A & B, Sirius A, Procyon A, Altair, Vega, and Fomalhaut offer the best chance of exoplanet detection using this technique.
Since an exoplanet will be easiest to detect when it is at its greatest angular distance from its parent star, we will be seeing only about 50% of its total reflected light. An Earth analog orbiting Alpha Centauri A would thus shine at visual magnitude +23.7 at 0.94″ angular distance, and for Alpha Centauri B the values would be +24.9 and 0.55″.
Other considerations include the advantage of an extremely faint occulting solar system object (making it easier to detect faint exoplanets during the occultation event), and the signal boost offered by observing in the infrared, since exoplanets will be brightest at these wavelengths.
A distant (and therefore slow-moving) TNO would be ideal, but the angular size of the TNO needs to be larger than the angular size of the occulted star. However, slow-moving objects mean that occultation events will be rare.
The best chance of making this a usable technique for exoplanet discovery would be a space-based observatory that could be positioned at the center of the predicted shadow and would be able to move along with the shadow to increase exposure times (Ahad, personal communication). It would be an interesting challenge in orbital mechanics to design the optimal base orbit for such a spacecraft. The spacecraft orbit would be adjusted to match the position and velocity of the occultation shadow for each event using an ion drive or some other electric propulsion system.
One final thought on the imaging necessary to detect exoplanets using this technique. With a traditional CCD you would need to begin and end the exoplanet imaging exposure(s) only while the parent star is being occulted. This would not be easy to do, and would require two telescopes – one for the occultation event detection and one for the exoplanet imaging. A better approach would be to use a Geiger-mode avalanche photodiode (APD). Here’s a description of the device captured in 2016 on the MIT Lincoln Labs Advanced Imager Technology website:
A Geiger-mode avalanche photodiode (APD), on the other hand, can be used to build an all-digital pixel in which the arrival of each photon triggers a discrete electrical pulse. The photons are counted digitally within the pixel circuit, and the readout process is therefore noise-free. At low light levels, there is still noise in the image because photons arrive at random times so that the number of photon detection events during an exposure time has statistical variation. This noise is known as shot noise. One advantage of a pixel that can digitally count photons is that if shot noise is the only noise source, the image quality will be the best allowed by the laws of physics. Another advantage of an array of photon counting pixels is that, because of its noiseless readout, there is no penalty associated with reading the imager out frequently. If one reads out a thousand 1-ms exposures of a static scene and digitally adds them, one gets the same image quality as a single 1-s exposure. This would not be the case with a conventional imager that adds noise each time it is read out.
References Ahad, A., “Detecting Habitable Exoplanets During Asteroidal Occultations”, International Journal of Scientific and Innovative Mathematical Research, Vol. 6(9), 25-30 (2018). MIT Lincoln Labs, Advanced Imager Technology, https://www.ll.mit.edu/mission/electronics/ait/single-photon-sensitive-imagers/passive-photon-counting.html. Retrieved March 17, 2016. NASA Exoplanet Archive https://exoplanetarchive.ipac.caltech.edu. Winn, J.N., “Exoplanet Transits and Occultations,” in Exoplanets, ed. Seager, S., University of Arizona Press, Tucson (2011).
Early in the morning of Tuesday, May 29, 2018, I was fortunate enough to record a 3.2 second occultation of the 12.6 magnitude star UCAC4 359-140328 in Sagittarius by the unnamed asteroid 29769, originally given the provisional designation 1999 CE28.
Not only is this the first time this asteroid has been observed to pass in front of a star, it is the smallest asteroid I have ever observed passing in front of a star. At an estimated diameter of 14.7 miles, had I been located just 7.4 miles either side of the centerline of the shadow path, I would have missed this event altogether! This is also the first positive event I’ve recorded for an (as yet) unnamed asteroid, and the first positive event I’ve recorded for an asteroid having more than a four-digit number (29769).
As you can see in the map above, the predicted shadow path was quite a ways northwest of my location. Even though I used the Gaia DR2 position for UCAC4 359-140328 for the path prediction, the existing orbital elements for asteroid 29769 did not yield a correspondingly accurate position for the asteroid.
Though a single chord across an asteroid does not give us any definitive information about its overall size and shape, it does give us a very accurate astrometric position that will be used to improve the orbital elements for this asteroid.
The central moment of this occultation event was 6:00:02.414 UT on May 29, 2018, which was about 20 seconds later than predicted. The astrometric equatorial coordinates for the star UCAC4 359-140328 referenced to the J2000 equinox (using Gaia DR2 with proper motion applied) are
UCAC4 359-140328
α = 18h 21m 01.6467s
δ = -18° 20′ 46.282″
Using JPL Horizons (with the extra precision option selected), the astrometric equatorial coordinates for the asteroid 29769 (1999 CE28), again referenced to the J2000 equinox, are
29769 (1999 CE28)
α = 18h 21m 01.6388s
δ = -18° 20′ 46.320″
As we can see above, the actual position of the asteroid at the time of the event was 0.0079 seconds of time east and 0.038 seconds of arc north of its predicted position. This observation will provide a high quality astrometric data point for the asteroid that will be used to improve its orbit. Gratifying!
As of this writing, there are 523,584 minor planets that have sufficiently well enough determined orbits to have received a number. Of these, only 21,348 have received names (4.1%). So, I guess you could say there is quite a backlog of numbered asteroids awaiting to receive names. The IAU should consider naming some minor planets after the most productive asteroid occultation observers around the world. There aren’t very many of us, and this would certainly be an encouragement to new and existing observers.
Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but since October 4, 1957 another “species” of sky vermin made their debut: artificial satellites. In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.
I’ve put together a video montage of satellites I’ve recorded between June 21, 2017 and October 20, 2017. The component events are presented chronologically as follows:
UT Date
6-21-2017
8-15-2017
9-4-2017
9-5-2017
9-12-2017
10-20-2017 (2 satellites)
You’ll notice that sometimes the satellite crosses the field as a moving “dash”. That’s because sometimes I used longer exposure times to record a fainter target star.
In general, the slower the satellite is moving across the field, the higher is its orbit around the Earth. One must also consider how much of the satellite’s orbital motion is along your line of sight to the satellite. In the following video clip, you’ll see a slow-moving “tumbler” satellite moving from right to left across the top of the field.
UT Date
8-25-2017
Target Star
Tycho 676-828-1
Asteroid
179462 (2002 AJ202)
On January 10th of this year, I figured out how to identify satellites crossing the telescope field of view using the amazing program Guide 9.1, which I use for all my observatory research work. On March 4th, I was hoping to be the first to record the asteroid 3706 Sinnott passing in front of a star. This asteroid is named after Sky & Telescope Senior Editor Roger Sinnott, whom I had the good fortune to work with in writing the article “A Roll-Down-Roof Observatory” in the May 1993 issue of Sky & Telescope, p. 90. Roger is amazing. He took an article that I had written and edited it in a way that only lightly touched my original text yet ended up saying what I wanted to say even better than I was able to say it myself. The mark of a great editor! Anyway, I’m sure Roger remembers me and I was looking forward to giving him the news that I had observed the first stellar occultation by “his” asteroid. Alas, it was not to be, because, as so often happens, the too-faint-to-be-seen asteroid passed either above or below the target star. The consolation prize, however, was recording a third stage Long March Chinese rocket booster (CZ-3B R/B; NORAD 43004U; International # 17069D) passing through the field. This rocket launched on November 5, 2017, and added two satellites to China’s Beidou positioning network. As you can see in the light curve below, the rotation period of the rocket booster is a bit longer than the 19 seconds of usable video I had.
UT Date
3-4-2018
Target Star
UCAC4 556-42881
Asteroid
3706 Sinnott
Once in a great while, I record a telescopic meteor. Here are two.
UT Date
7-15-2017
3-4-2018
Target Star
Tycho 6269-2747-1
UCAC4 561-14746
Asteroid
17136(1999 JE82)
6890 Savinykh
References
Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21
Under the direction of Friedrich Argelander (1799-1875), astronomers at the Bonn Observatory spent seven years (1852 to 1859) measuring the positions and magnitudes of roughly 324,000 stars, one star at a time. This phenomenal work resulted in the Bonner Durchmusterung (BD) catalog and atlas, which included stars down to approximately magnitude 9.5 and is a tribute to the foresight of Argelander and the diligence of his small staff. The Bonner Durchmusterung was the last star catalog to be produced without the benefit of photography, and it is certainly the most comprehensive of the pre-photographic atlases.
Back in 2007, Alan MacRobert stated (Sky & Telescope, July 2007, p. 59), “Someday machines will measure the brightness of every star in the sky to some amazingly deep magnitude many times a night, and blind software will compile and analyze light curves automatically.” No doubt, he is correct, but he does add that this has not happened yet, despite years of pregnant expectations.
But we are getting closer to that day, with the Large Synoptic Survey Telescope (LSST) scheduled to come online in 2022 and many other similar survey instruments in the pipeline or already operational. That is one reason as an amateur astronomer with limited resources (including time) I focus on observing the occultation of stars by asteroids and trans-Neptunian objects. It is one of the few areas where an amateur observational astronomer can provide location-dependent observations. You are either in the shadow path or you are not. Though truth be told I would rather be studying exoplanets, we can only do what we have the resources to do—regardless of talent or potential.
History is full of examples of skills and techniques made obsolete almost overnight by new technologies (or a different point of view), but what is seldom recorded is the sense of desolation and indeed mortality experienced by those unfortunate enough to live to see that their highly-developed skills are no longer wanted or needed. As my meteor-watching friend Paul Martsching has said, “It is good we don’t live forever: we are a product of our times.” He realizes full well that someday automated systems will count every meteor above the horizon far better and more completely than any visual meteor observer can, but for many years he has carefully recorded meteor activity many nights a year. The data he collects will always be relevant as part of the historical record, at least, and the sheer joy of being out under the stars and away from light pollution can never be replaced by a computer. To us, astronomy is something much deeper than what can be delivered through a computer screen.
We are a product of our times, and as we approach the twilight (or autumn) of our lives we don’t necessarily feel compelled to embrace every new thing that comes along. Peace.
From the standpoint of daily life, however, there is one thing we do know: that we are here for the sake of each other—above all for those upon whose smile and well-being our own happiness depends, and also for the countless unknown souls with whose fate we are connected by a bond of sympathy. Many times a day I realize how much my own outer and inner life is built upon the labors of my fellow men, both living and dead, and how earnestly I must exert myself in order to give in return as much as I have received. – Albert Einstein (1879-1955)
(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.
