Nearest Exoplanets

There are 33 confirmed exoplanets within 15 light years of our solar system, with more certainly on the way as a number of unconfirmed exoplanets are under ongoing investigation.

Here’s a table of all known planets within 15 light years of the Sun, including the eight planets of our own solar system for comparison.

Click the link below for a more convenient view of the entire table in a separate tab.

Planet mass and radius are given in terms of Earth’s mass and radius. The reason the radius of all the exoplanets listed here is “unknown” is because all of these planets have been detected using the radial velocity and/or astrometric method. Only the transit method provides a reliable way to measure an exoplanet’s size, but the nearest stars that host transiting exoplanets are 21.3 ly and 22.4 ly distant (HD 219134 and LTT 1445, respectively). Our limit here is 15 ly.

A side note about transiting exoplanets. In order for us to see an exoplanet transiting its host star, the exoplanet’s orbital plane has to be fortuitously aligned quite close to our line of sight. Since even these nearest stars are very far away in comparison to the size of our solar system, we are stuck with the line of sight we have. What percentage of all exoplanets out there might we detect using the transit method? That depends, of course, on the orientation of the exoplanet’s orbital plane but also the size of the star (and the planet if it is large) and the distance of the exoplanet from that star. Roughly, only about 1 in 200 exoplanets or about 0.5% can be detected using the transit method.

Luminosity is the host star’s luminosity in terms of our Sun’s luminosity. Bolometric luminosity is used where available; otherwise, optical luminosity is used.

The average distance of the planet from the star is calculated from the semi-major axis and the orbital eccentricity. We then calculate the incident stellar flux using the average distance of the planet from the star and the luminosity of the star, normalized to what the Earth receives (0.9997 and not 1.oooo because the Earth, on average, is more than 1 AU from the Sun). The relevant equation is:

\frac{\textrm{L}}{\bar{\textrm{d}}^{2}}\cdot\phi_{\oplus }

where L is the luminosity of the star in terms of the Sun’s luminosity
   and d-bar is the average distance of the planet from the star in AU
   and Φ is the incident stellar flux at Earth’s average distance from the Sun
             in proportional units of solar luminosities per AU2

This calculation, of course, makes no assumptions about the albedo of the planet nor whatever atmosphere the planet may or may not have. It is simply a calculation of stellar radiation per unit area received at the planet’s distance from the star.

Here’s an example from the table. Mercury, on average, receives 6.4 times as much energy per unit area as does the Earth, whereas Neptune receives only 0.0011 as much as the Earth.

Some Key Takeaways

  • The most luminous star that is known to host exoplanets within 15 light years of our solar system, Epsilon Eridani, is only 32% as bright as the Sun.
  • Eight of these exoplanets receive an amount of energy from their star that is comparable to what the Earth receives from the Sun: Gliese 1061 d (0.56), Proxima Centauri b (0.66), Gliese 687 b (0.78), Luyten’s Star b (1.05), Teegarden’s Star b (1.07), Wolf 1061 c (1.37), Gliese 1061 c (1.40), and Ross 128 b (1.42).
  • The most massive of these exoplanets is Epsilon Eridani b, weighing in at 311 earth-masses, comparable to Jupiter in our own solar system (318).

I’d like to conclude by noting that I will do my best to keep this table up-to-date, but if you see something that needs changing before I do, by all means post a comment here and I will make the correction or addition.

Minor Planets Named After Their Discoverers

To the best of my knowledge, only 19 minor planets have been named after their discoverers. While the discoverer has first naming rights, they cannot name a minor planet after themselves, though they can (and sometimes do) name a minor planet after a spouse, parent, or child.

Of course, many minor planet discoverers have minor planets named after them, but almost always these are discoveries by someone else who decides to name one of “their” minor planets after the other discoverer.

In the rare situation when someone decides (and has the authority) to name a discoverer’s minor planet after the discoverer, it is almost always a posthumous honor. Comet discoveries, on the other hand, are automatically named after their discoverer(s).

I have reader Rafael to thank for letting me know that Eugène Delporte does indeed have an asteroid he discovered named after him (see comments after Eugène Delporte and the Constellation Jigsaw) and this got me wondering if there were other examples. I wrote a SAS program to do some fuzzy matching between asteroid name and asteroid discoverer, and came up with the following list. Let me know if there are any others I missed, and I will include them here.

726 Joëlla
Discovered 1911 Nov 22 by Joel Hastings Metcalf (1866-1925) at Winchester, Massachusetts.

792 Metcalfia
Discovered 1907 Mar 20 by Joel Hastings Metcalf (1866-1925) at Taunton, Massachusetts.

989 Schwassmannia
Discovered 1922 Nov 18 by Arnold Schwassmann (1870-1964) at Bergedorf, Germany.

1074 Beljawskya
Discovered 1925 Jan 26 by Sergey Ivanovich Belyavskij (1883-1953) at Simeïs, Crimea.

1111 Reinmuthia
Discovered 1927 Feb 11 by Karl Reinmuth (1892-1979) at Heidelberg, Germany.

1274 Delportia
Discovered 1932 Nov 28 by Eugène J. Delporte (1882-1955) at Uccle, Belgium.

1596 Itzigsohn
Discovered 1951 Mar 8 by Miguel Itzigsohn (1908–1978) at La Plata, Argentina.

1648 Shajna
Discovered 1935 Sep 5 by Pelageya Fedorovna Shajn (1894-1956) at Simeïs, Crimea.

1655 Comas Solá
Discovered 1929 Nov 28 by José Comas Solá (1868-1937) at Barcelona, Spain.

1666 van Gent
Discovered 1930 Jul 22 by Hendrik van Gent (1899-1947) at Johannesburg, South Africa.

1777 Gehrels
Discovered 1960 Sep 24 by C. J. van Houten, I. van Houten-Groeneveld, and Tom Gehrels (1925-2011) at Palomar Mountain, California.

1927 Suvanto
Discovered 1936 Mar 18 by Rafael Suvanto (1909-1940) at Turku, Finland.

2044 Wirt
Discovered 1950 Nov 8 by Carl A. Wirtanen (1910-1990) at Mount Hamilton, California.

2246 Bowell
Discovered 1979 Dec 14 by Edward L. G. Bowell (1943-2023) at Anderson Mesa, Arizona.

3019 Kulin
Discovered 1940 Jan 7 by György Kulin (1905-1989) at Budapest, Hungary.

5540 Smirnova
Discovered 1971 Aug 30 by Tamara Mikhajlovna Smirnova (1935-2001) at Nauchnyj, Crimea.

5900 Jensen
Discovered 1986 Oct 3 by Poul B. Jensen (?-) at Brorfelde, Denmark.

19911 Rigaux
Discovered 1933 Mar 26 by Fernand Rigaux (1905-1962) at Uccle, Belgium.

96747 Crespodasilva
Discovered 1999 Aug 16 by Lucy d’Escoffier Crespo da Silva (1978-2000) at Westford, Massachusetts.

Incidentally, here are the three most prolific minor planet discoverers that still have an unnamed minor planet discovery that could be named after them. There are, of course, many others who deserve this honor.

Eleanor F. Helin (1932-2009)
Even though 3267 Glo is named after her nickname “Glo”, why not designate one of her discoveries as Helin or Eleanor Helin or Eleanorhelin? There are many still available, beginning with 5131 (1990 BG).

Carolyn Shoemaker (1929-2021)
Though 4446 Carolyn is named after her, why not designate one of her discoveries as Carolyn Shoemaker or Carolynshoemaker? There are many still available, beginning with 48576 (1994 NN2).

Gary Hug (1950-)
There are many still available, including 32165 (1998 FS92).

The Mysterious Case of 55 Herculis

55 Her (near 54 Her, shown above) was visible as late as 1782, but by 1791 it had disappeared
(Click on the image above for a larger view.)

I was fascinated to read the letter from Oleksiy V. Arkhypov (Kharkiv, Ukraine) in the February 2025 issue of Sky & Telescope, p. 6, where he describes a 5th-magnitude star in the constellation Hercules that has apparently disappeared. John Flamsteed (1646-1719) had recorded the star at the end of the 17th century. Flamsteed listed the brighter stars in each constellation in order of right ascension at the time, but did not number them. That task fell to Joseph Jérôme de Lalande (1732–1807) who assigned what we now know as the “Flamsteed numbers” to each of the stars in Flamsteed’s catalogue. Two adjacent stars in Hercules in Flamsteed’s catalogue were given the designations 54 Her and 55 Her.

William Herschel (1738-1822) observed both stars on October 10, 1781 (and had noted that they were both red in color) and again on April 11, 1782, but on May 24, 1791 (and afterwards), only 54 Her was visible. Apparently, 55 Her disappeared from sight between 1782 and 1791, and it hasn’t been seen since.

In Herschel’s own words:

On the Disappearance of the 55th Herculis.

Among the changes that happen in the sidereal heavens we enumerate the loss of stars; but, notwithstanding the real destruction of an heavenly body may not be impossible, we have some reasons to think that the disappearance of a star is probably owing to causes which are of the same nature with those that act upon periodical stars, when they occasion their temporary occultations. This subject, however, being of great extent and consequence, we shall not enter into it at present, but only relate a recent instance of the kind.

Two stars of the 5th magnitude, whose places we find inserted in all our best catalogues, were to be seen in the neck of Hercules. They are the 54th and 55th of Flamsteed’s, in that constellation. In the year 1781, the 10th of October, I examined them both, and marked down their colour, red. The 11th of April, 1782, I looked at them again, and noted my having seen them distinctly, with a power of 460; and that they were single stars.

The 24th of last May, I missed one of the two, and examining the spot again the 25th, and many times afterwards, found that one of them was not to be seen. The situation of the stars is such that, not having fixed instruments, I could not well determine which of the two was the lost one. I therefore requested the favour of my much esteemed friend, the astronomer royal, to ascertain the remaining star ; and it appears from Dr. Maskelyne’s answer to my letter, that the 55th Herculis is the one which we have lost.

The coordinates for 54 Her are:
α2000 = 16h 55m 22s, δ2000 = +18° 26′ 00″

Recent arXiv:astro-ph Picks: December 2024

Here are some recent submissions on astro-ph that I found to be especially interesting. Text excerpts below are quoted directly from the articles. My comments are in italics.

Short-Term Evolution and Risks of Debris Cloud Stemming from Collisions in Geostationary Orbit
https://arxiv.org/abs/2412.13586

The geostationary orbit is a popular orbit for communication, meteorological, and navigation satellites due to its apparent motionless. Nearly all geostationary satellites are positioned in a circular orbit with a radius of 42,164 km, making this region particularly vulnerable to space traffic accidents due to the high concentration of objects and the absence of natural debris-clearing mechanisms. The growing population in geostationary region raises concerns about the potential risks posed by fragments stemming from explosions and collisions, particularly following the breakup of Intelsat-33e, which remained operational in geostationary orbit until October 19, 2024.

A breakup event generates a large number of fragments of varying sizes. In the geostationary region, only fragments larger than 1 meter are routinely tracked by the Space Surveillance Network, as the sensitivity of ground-based sensors decreases significantly with distance. However, small, non-trackable fragments can still cause catastrophic damage to spacecraft. The collision velocity of spacecraft in geostationary orbit can reach up to 4 km/s, while micro-meteoroids may hit at speeds of up to 72 km/s.

The impact of a debris cloud is inherently global as it disperses around the entire Earth.

By 2024, over 1,000 objects have been observed near the geostationary orbit (GEO). Nearly all objects exhibit inclinations of less than 15 degrees, with the majority having inclinations of less than 1 degree. Once a fragmentation event occurs, the GEO objects will be exposed to considerable risks, as they are densely clustered along a single ring above the Equator.

More about Intelsat 33e and its breakup:
https://en.wikipedia.org/wiki/Intelsat_33e


Sun-like stars produce superflares roughly once per century
https://arxiv.org/abs/2412.12265

Stellar superflares are energetic outbursts of electromagnetic radiation, similar to solar flares but releasing more energy, up to 1036 erg on main sequence stars. It is unknown whether the Sun can generate superflares, and if so, how often they might occur. We used photometry from the Kepler space observatory to investigate superflares on other stars with Sun-like fundamental parameters. We identified 2889 superflares on 2527 Sun-like stars, out of 56450 observed. This detection rate indicates that superflares with energies >1034 erg occur roughly once per century on stars with Sun-like temperature and variability. The resulting stellar superflare frequency-energy distribution is consistent with an extrapolation of the Sun’s flare distribution to higher energies, so we suggest that both are generated by the same physical mechanism.

Solar flares are sudden local bursts of bright electromagnetic emission from the Sun, which release a large amount of energy within a short interval of time. The increase in short-wavelength solar radiation during flares influences the Earth’s upper atmosphere and ionosphere, sometimes causing radio blackouts and ionosphere density changes. Solar flares are frequently accompanied by the expulsion of large volumes of plasma, known as coronal mass ejections (CMEs), which accelerate charged particles to high energies. When these solar energetic particles (SEPs) reach Earth, they cause radiation hazards to spacecraft, aircraft and humans. Extreme SEP events can produce isotopes, called cosmogenic isotopes, which form when high-energy particles interact with the Earth’s atmosphere. These isotopes are then recorded in natural archives, such as tree rings and ice cores. The total amount of energy released by each flare varies by many orders of magnitude, as determined by a complex interplay between the physical mechanisms of particle acceleration and plasma heating in the Sun’s
atmosphere.

Solar flares have been observed for less than two centuries. Although thousands of them have been detected and measured, only about a dozen are known to have exceeded a bolometric (integrated over all wavelengths) energy of 1032 erg. Among them was the Carrington Event on 1 September 1859, which was accompanied by a CME that had the strongest recorded impact on Earth. Modern estimates of the Carrington Event’s total bolometric energy are 4 × 1032 to 6 × 1032 erg.

It is unknown whether the Sun can unleash flares with even higher energies, often referred to as superflares, and if so, how frequently that could happen. The period of direct solar observations is too short to reach any firm conclusions. There are two indirect methods to investigate the potential for more intense flares on the Sun. One method uses extreme SEP events recorded in cosmogenic isotope data, which have been used to quantify the occurrence rate of strong CMEs reaching Earth over the past few millennia. There are five confirmed (and three candidate) extreme SEP events that are known to have occurred in the last 10,000 yr, implying a mean occurrence rate of ∼ 10−3 yr−1. However, the relationship between SEPs and flares is poorly understood, especially for the stronger events.

A second method is to study superflares on stars similar to the Sun. If the properties of the observed stars sufficiently match the Sun, the superflare occurrence rate on those stars can be used to estimate the rate on the Sun.

We found that Sun-like stars produce superflares with bolometric energies > 1034 erg roughly once per century. That is more than an order of magnitude more energetic than any solar flare recorded during the space age, about sixty years. Between 1996 and 2012 twelve solar flares had bolometric energies > 1032 erg, but none were > 1033 erg. The most powerful solar flare recorded occurred on 28 October 2003, with an estimated bolometric energy of 7 × 1032 erg, which exceeds estimates for the Carrington Event (4 × 1032 to 6 × 1032 erg).

We cannot exclude the possibility that there is an inherent difference between flaring and non-flaring stars that was not accounted for by our selection criteria. If so, the flaring stars in the Kepler observations would not be representative of the Sun. Approximately 30% of flaring stars are known to have a binary companion. Flares in those systems might originate on the companion star or be triggered by tidal interactions. If instead our sample of Sun-like stars is representative of the Sun’s future behavior, it is substantially more likely to produce a superflare than was previously thought.

More about the Carrington Event:
https://en.wikipedia.org/wiki/Carrington_Event


ChronoFlow: A Data-Driven Model for Gyrochronology
https://arxiv.org/abs/2412.12244

Gyrochronology is a technique for constraining stellar ages using rotation periods, which change over a star’s main sequence lifetime due to magnetic braking. This technique shows promise for main sequence FGKM stars, where other methods are imprecise. However, models have historically struggled to capture the observed rotational dispersion in stellar populations. To properly understand this complexity, we have assembled the largest standardized data catalog of rotators in open clusters to date, consisting of ~7,400 stars across 30 open clusters/associations spanning ages of 1.5 Myr to 4 Gyr.

Stars in open clusters are all about the same age, so this is highly useful in training models that use stellar rotation periods to determine stellar age.
https://en.wikipedia.org/wiki/Gyrochronology


On The Lunar Origin of Near-Earth Asteroid 2024 PT5
https://arxiv.org/abs/2412.10264

The Near-Earth Asteroid (NEA) 2024 PT5 is on an Earth-like orbit which remained in Earth’s immediate vicinity for several months at the end of 2024. PT5’s orbit is challenging to populate with asteroids originating from the Main Belt and is more commonly associated with rocket bodies mistakenly identified as natural objects or with debris ejected from impacts on the Moon. We obtained visible and near-infrared reflectance spectra of PT5 with the Lowell Discovery Telescope and NASA Infrared Telescope Facility on 2024 August 16. The combined reflectance spectrum matches lunar samples but does not match any known asteroid types—it is pyroxene-rich while asteroids of comparable spectral redness are olivine-rich. Moreover, the amount of solar radiation pressure observed on the PT5 trajectory is orders of magnitude lower than what would be expected for an artificial object. We therefore conclude that 2024 PT5 is ejecta from an impact on the Moon, thus making PT5 the second NEA suggested to be sourced from the surface of the Moon. While one object might be an outlier, two suggest that there is an underlying population to be characterized. Long-term predictions of the position of 2024 PT5 are challenging due to the slow Earth encounters characteristic of objects in these orbits. A population of near-Earth objects which are sourced by the Moon would be important to characterize for understanding how impacts work on our nearest neighbor and for identifying the source regions of asteroids and meteorites from this under-studied population of objects on very Earth-like orbits.

Perhaps the most significant conclusion to finding a second near-Earth object with an apparently Moon-like surface composition is the realization of lunar ejecta as a genuine population of objects. The Quasi-Satellite Kamo‘oalewa has a slightly redder spectrum than 2024 PT5, but the higher quality of our data at longer wavelengths (the Quasi-Satellite was significantly dimmer, so only photometry was obtained beyond ≈ 1.25μm) makes a discussion of how different the two spectra are only qualitative. At the very least, the two lunar NEOs do not look identical. Sharkey et al. (2021) argued that the red spectrum of Kamo‘oalewa was partially due to space weathering – an exposure time of a few million years was likely sufficient to explain its surface properties and was similar to its approximate dynamical lifetime and even the age of the crater that Jiao et al. (2024) suggested it came from, Giordano Bruno. If correct, perhaps 2024 PT5 has a somewhat younger surface than the larger Kamo‘oalewa. In any case, PT5 is smaller than Kamo‘oalewa and thus the craters that are energetic enough to produce an object its size are more common – a more recent ejection age, and thus a ‘younger’ surface might be preferred from that argument as well. (Granted, smaller fragments would be more common than larger ones in cratering events of any size as well.) Further work to study these two objects and to find more lunar-like NEOs will be needed to ascertain the origin of these differences and how they can be related to the circumstances of their creation. At any rate, the smaller size of PT5 means that we are approaching being able to study the impactors and outcomes from the kinds of small impacts seen regularly by the Lunar Reconaissance Orbiter.

For more information about 2024 PT5 and Kamo‘oalewa:
https://en.wikipedia.org/wiki/2024_PT5
https://en.wikipedia.org/wiki/469219_Kamo%CA%BBoalewa


Call to Protect the Dark and Quiet Sky from Harmful Interference by Satellite Constellations
https://arxiv.org/abs/2412.08244

The growing number of satellite constellations in low Earth orbit (LEO) enhances global communications and Earth observation, and support of space commerce is a high priority of many governments. At the same time, the proliferation of satellites in LEO has negative effects on astronomical observations and research, and the preservation of the dark and quiet sky. These satellite constellations reflect sunlight onto optical telescopes, and their radio emission impacts radio observatories, jeopardising our access to essential scientific discoveries through astronomy. The changing visual appearance of the sky also impacts our cultural heritage and environment. Both ground-based observatories and space-based telescopes in LEO are affected, and there are no places on Earth that can escape the effects of satellite constellations given their global nature. The minimally disturbed dark and radio-quiet sky1 is crucial for conducting fundamental research in astronomy and important public services such as planetary defence, technology development, and high-precision geolocation.

Some aspects of satellite deployment and operation are regulated by States and intergovernmental organisations. While regulatory agencies in some States have started to require operators to coordinate with their national astronomy agencies over impacts, mitigation of the impact of space objects on astronomical activities is not sufficiently regulated.

1We refer to the radio-quiet sky as simply the ‘quiet sky’

To address this issue, the CPS [International Astronomical Union (IAU) Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS)] urges States and the international community to:

1) Safeguard access to the dark and quiet sky and prevent catastrophic
loss of high quality observations.

2) Increase financial support for astronomy to offset and compensate the impacts on observatory operations and implement mitigation measures at observatories and in software.

3) Encourage and support satellite operators and industry to collaborate with the astronomy community to develop, share and adopt best practices in interference mitigation, leading to widely adopted standards and guidelines.

4) Provide incentive measures for the space industry to develop the required technology to minimise negative impacts. Support the establishment of test labs for brightness and basic research into alternate less reflective materials
and reduction of unwanted radiation in the radio regime for spacecraft manufacturing.

5) In the longer term, establish regulations and conditions of authorization and supervision based on practical experience as well as the general provisions of international law and main principles of environmental law to codify industry best practices that mitigate the negative impacts on astronomical observations. Satellites in LEO should be designed and operated in ways that minimise adverse effects on astronomy and the dark and quiet sky.

6) Continue to support finding solutions to space sustainability issues, including the problem of increasing space debris leading to a brighter sky. Minimising the production of space debris will also benefit the field of astronomy and all sky observers worldwide.

The elephant in the room—not specifically mentioned in this report—is that countries and companies should be sharing satellite constellations as much as possible to minimize the number of satellite constellations in orbit. This is analogous to the co-location often required for terrestrial communication towers. Our current satellite constellation predicament illustrates yet another reason why we need a binding set of international laws that apply to all nations and are enforced by a global authority. The sooner we have this the better, as our cultural survival—if not our physical survival—may depend upon it.


A New Method to Derive an Empirical Lower Limit on the Mass Density of a UFO
https://arxiv.org/abs/2412.12142

I derive a lower limit on the mass of an Unidentified Flying Object (UFO) based on measurements of its speed and acceleration, as well as the infrared luminosity of the airglow around it. If the object’s radial velocity can be neglected, the mass limit is independent of distance. Measuring the distance and angular size of the object allows to infer its minimum mass density. The Galileo Project will be collecting the necessary data on millions of objects in the sky over the coming year.

Any object moving through air radiates excess heat in the form of infrared airglow luminosity, L. The airglow luminosity is a fraction of the total power dissipated by the object’s speed, v, times the frictional force of air acting on the object. The radiative efficiency depends on the specific shape of the object and the turbulence and thermodynamic conditions in the atmosphere around it. If the object accelerates, then this friction force must be smaller than the force provided by the engine which propels the object. The net force equals the object’s mass, M, times its acceleration, a.

In conclusion, one gets an unavoidable lower limit on the mass of an accelerating object. The object’s mass must be larger than the infrared luminosity from heated air around it, divided by the product of the object’s acceleration and speed.

This limit provides an elegant way to constrain the minimum mass of Unidentified Flying Objects (UFOs), also labeled as Unidentified Anomalous Phenomena (UAPs). To turn the inequality into an equality, one needs to know the detailed object shape and atmospheric conditions around the object.

The first Galileo Project Observatory at Harvard University collects data on ∼ 105 objects in the sky every month. A comprehensive description of its commissioning data on ∼ 5 × 105 objects was provided in a recent paper (Dominé et al. 2024). The data includes infrared images captured by an all-sky Dalek array of eight uncooled infrared cameras placed on half a sphere.

Within the coming month, the Galileo Project’s research team plans to employ multiple Daleks separated by a few miles, in order to measure distances to objects through the method of triangulation.

If the measured velocity and acceleration of a technological object are outside the flight characteristics and performance envelopes of drones or airplanes, then the object would be classified by the Galileo Project’s research team as an outlier. In such a case, it would be interesting to calculate the minimum mass density of the object. If the result exceeds normal solid densities, then the object would qualify as anomalous, a UAP. Infrared emission by the object would be a source of confusion, unless the object is resolved and the emission from it can be separated from the heated air around it.

All flying objects made by humans have a volume-averaged mass density ⟨ρ⟩ which is orders of magnitude below 22.6 g cm−3, the density of Osmium – which is the densest metal known on Earth. A UFO with a higher mass density than Osmium would have to carry exotic material, not found on Earth.

By summer 2025, there will be three Galileo Project observatories operating in three different states within the U.S. and collecting data on a few million objects per year. With new quantitative data on infrared luminosities, velocities and accelerations of technological objects, it would be possible to check whether there are any UFOs denser than Osmium.

I admire the author, Avi Loeb, Harvard astrophysics professor, for his creative approaches to interesting problems outside the mainstream that many of his colleagues tend to avoid. Lately, he’s been focusing a lot on technosignatures, and I imagine he has a keen interest in the recent spate of unexplained nighttime drone sightings in New Jersey and elsewhere. For more about Loeb and the Galileo Project:
https://en.wikipedia.org/wiki/Avi_Loeb
https://en.wikipedia.org/wiki/The_Galileo_Project


Beyond CCDs: Characterization of sCMOS detectors for optical astronomy
https://arxiv.org/abs/2409.16449

Modern scientific complementary metal-oxide semiconductor (sCMOS) detectors provide a highly competitive alternative to charge-coupled devices (CCDs), the latter of which have historically been dominant in optical imaging. sCMOS boast comparable performances to CCDs with faster frame rates, lower read noise, and a higher dynamic range. Furthermore, their lower production costs are shifting the industry to abandon CCD support and production in favour of CMOS, making their characterization urgent. In this work, we characterized a variety of high-end commercially available sCMOS detectors to gauge the state of this technology in the context of applications in optical astronomy. We evaluated a range of sCMOS detectors, including larger pixel models such as the Teledyne Prime 95B and the Andor Sona-11, which are similar to CCDs in pixel size and suitable for wide-field astronomy. Additionally, we assessed smaller pixel detectors like the Ximea xiJ and Andor Sona-6, which are better suited for deep-sky imaging. Furthermore, high-sensitivity quantitative sCMOS detectors such as the Hamamatsu Orca-Quest C15550-20UP, capable of resolving individual photoelectrons, were also tested. In-lab testing showed low levels of dark current, read noise, faulty pixels, and fixed pattern noise, as well as linearity levels above 98% across all detectors. The Orca-Quest had particularly low noise levels with a dark current of 0.0067±0.0003 e/s (at −20C with air cooling) and a read noise of 0.37±0.09 e using its standard readout mode. Our tests revealed that the latest generation of sCMOS detectors excels in optical imaging performance, offering a more accessible alternative to CCDs for future optical astronomy instruments.

The Hamamatsu Orca-Quest CP15550-20UP, simply called Orca-Quest, is advertised as being a quantitative CMOS detector with extremely low noise levels and photoelectron counting capabilities. It features a custom 9.4-megapixel sensor with 4.6 × 4.6 μm pixels. The Orca-Quest has two scan modes that were characterized: standard and ultra-quiet. The ultra-quiet mode has a much lower frame rate at 5 frames per second (fps) compared to the standard mode’s 120 fps, which allows for much lower read noise. Also characterized was the ‘photon number resolving’ readout mode which claims to report the integer number of incident photoelectrons based on a proprietary calibrated algorithm using the ultra-quiet scan. The Orca-Quest has a detector-imposed temperature lock at −20C when air-cooled. The standard and ultra-quiet modes are 16-bit, with a saturation limit of 65536 ADU while the photon number resolving mode has a saturation limit of only 200 ADU. The Orca-Quest boasts a peak quantum efficiency of 85%.

Unlike CCDs, which use a single global amplifier with a shift register, sCMOS pixels have individual readout electronics, requiring each pixel to be tested as an independent detector. Historically, this led to high fixed pattern noise in CMOS detectors, but we found negligible fixed pattern noise in almost all the detectors we analyzed pixel-wise.

4534 Rimskij-Korsakov

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)]
  • Russian Easter Festival Overture
  • Scheherazade
  • Suite from The Snow Maiden
  • Symphony No. 2, “Antar”
  • The Tale of Tsar Saltan, Suite

Comet Tsuchinshan-ATLAS (C/2023 A3)

Comet Tsuchinshan-ATLAS (C/2023 A3)
October 20, 2024 0208 UT, west of Tucson, Arizona
Photograph by David Oesper

A bright comet with a long tail is just now emerging into our evening sky after passing perihelion, and today around 9:08 a.m. MST it passed closest to the Earth at a distance of 0.47 AU.

Even though there is currently moonlight interference and the comet’s head is on the WSW horizon at the end of astronomical twilight (here in Tucson), the tail may be visible even as early as tonight, and each evening going forward Comet Tsuchinshan-ATLAS will be rising higher in the WSW sky.

Our first chance this month to see Comet Tsuchinshan-ATLAS at least 10° above the horizon in a sky free of twilight and moonlight will come next Saturday evening, but you should definitely make an effort to get out of the city to a dark rural location free of light pollution to get the best view.

Here’s a dark-sky ephemeris for Comet Tsuchinshan-ATLAS for Tucson, Arizona for October and November. Since the comet is moving away from both the Sun and the Earth, the sooner you make an effort to see this spectacular comet, the better!

How Far the Sun

How do we know our Sun is 93 million miles (150 million km) away1?

The ancient Greek astronomer and mathematician Aristarchus of Samos, who lived around 2,300 years ago, was probably the first person who made a reasonable attempt to determine the distance to the Sun.

Using a method of geometric analysis developed by Euclid (trigonometry had not yet been invented), Aristarchus measured the angle between the half-lit Moon and the Sun and determined that the Sun is 18 to 20 times farther away than the Moon.  Though he fell far short of the actual value of 389 due to the extreme difficulty of making accurate measurements using the instruments and methods available to him, Aristarchus showed the way for future generations of astronomers to determine the true distance to the Sun.

Determining the actual distance (and not the relative distance) to the Sun had to wait for Kepler’s Third Law of planetary motion that relates a planet’s orbital period to its distance from the Sun, the invention of the telescope, and Isaac Newton’s laws of motion and gravitation.

P^{2}\propto a^{3}

Distances within the solar system can be determined using trigonometry and parallax, which is the apparent shift of an object against the distant background stars as seen from different locations.

Hold your thumb at arm’s length and alternate between right and left eye open to see the parallactic shift.
Bring your thumb closer, and the shift is greater.

Measuring the parallax to a Sun-orbiting object (such as Mars) from two different locations on the Earth’s surface allows us to measure its distance and, thanks to Kepler and Newton, sets the scale for the entire solar system.  The true distance of each planet from the Sun can then be mathematically determined.  This was first accomplished in 1672, and has been done many times since, with ever-improving accuracy.

Observations of the position of Mars by Giovanni Cassini at Paris and Jean Richer at Cayenne
allowed the first determination of the distance to Mars using trigonometric parallax in 1672.

Today, we have even better methods to determine the scale of the solar system: timing radar reflections off of solar system objects, and measuring travel time for radio communications between Earth and spacecraft.  Both radar and radio signals travel at the speed of light, which is very well determined.

1Approximate average distance

Hale, Hooker, Hubble, Humason

Edwin Powell Hubble (1889-1953) was born in Marshfield, Missouri, nine years after a devastating F4 tornado destroyed most of the town, killing 99 people and injuring 100. The Hubble family moved to Wheaton, Illinois (near Chicago) the year Edwin was born.

After receiving a B.S. degree from the University of Chicago in 1910, Hubble spent three years at Oxford University as a Rhodes Scholar. The experience must have made quite an impression on young Hubble, as he returned to the U.S. with an affected British accent and other mannerisms (such as smoking a pipe) that stayed with him (and sometimes irritated others) for the rest of his life.

George Ellery Hale (1868-1938) offered Hubble a job at the Mount Wilson Observatory in 1919, and that same year also hired a talented man who would soon become Hubble’s assistant, Milton Humason (1891-1972), just as Mt. Wilson’s 100-inch Hooker telescope (the largest in the world at that time) started to see regular use.

Hubble identified Cepheid variables in M31, the Andromeda Nebula (and some other spiral nebulae), using the 100-inch in 1922-1923. From those observations, Hubble determined without a shadow of doubt that the Andromeda Nebula is in fact another galaxy of stars lying far beyond our own Milky Way galaxy. Up until this time, there was great debate about whether “spiral nebulae” like M31 were within our own galaxy or beyond it. Many thought that our galaxy was the entire universe. Thanks to Edwin Hubble and those who followed him, we now know that our galaxy is but one of many billions in this unimaginably vast universe we are lucky enough to explore.

How did Hubble use the faint Cepheid variables to determine the distance to M31? Cepheid variables are very luminous yellow giant and supergiant stars whose luminosity is directly related to the period of time it takes for the star to vary in brightness from brightest to dimmest to brightest again. The longer the period, the brighter the star really is. Knowing the apparent brightness of a star (dependent on distance), and knowing its true brightness (not dependent on distance), we can easily calculate the distance to the star. In the case of M31, the Andromeda Galaxy, we now know its distance to be 2.48 ± 0.04 million light years. M31 and the Milky Way are comparable in size and mass, and are by far the two largest galaxies of the Local Group, which contains at least 80 members. M31 and our Milky Way are moving towards each other due to gravitational attraction, and they will “collide” in about 4 to 5 billion years, probably leading to the formation of a giant elliptical or lenticular galaxy. But no one on Earth will witness this event. Due to the warming Sun, the surface of the Earth will become lifeless in a billion years or so.

Maria Mitchell: America’s First Female Astronomy Professor

Maria (pronounced Ma-RYE-ah) Mitchell (1818-1889), America’s first female professor of astronomy, was born August 1, 1818 on Nantucket Island (Massachusetts). Her interest in astronomy was encouraged by her father, and she assisted him with his research at a time when few women were allowed an opportunity to do scientific research. She discovered a comet in 1847 at the age of 29, and this brought her fame as one of America’s few women scientists. She was employed for many years as a computer (a person who performs lengthy mathematical calculations), and then taught astronomy at Vassar College for many years (1865-1888), a women’s college in Poughkeepsie, New York. At Vassar, she was also the director of the Vassar College Observatory. A devoted teacher, she believed that students learn best by doing real research projects. In 1869, she traveled to Burlington, Iowa with six of her students to observe a total solar eclipse.

Seven years after the death of Maria Mitchell, her sister, Phebe Mitchell Kendall, (1828-1907) compiled a book, Maria Mitchell: Life, Letters, and Journals (1896).

The Maria Mitchell Observatory was established on Nantucket Island in 1908, and today continues its long legacy of public outreach and undergraduate research.

“When we are chafed and fretted by small cares, a look at the stars will show us the littleness of our own interests.”

“We travel to learn; and I have never been in any country where they did not do something better than we do it, think some thoughts better than we think, catch some inspiration from heights above our own.”

“Question everything.”

“The best that can be said of my life so far is that it has been industrious, and the best that can be said of me is that I have not pretended to what I was not.”

Quotes by Maria Mitchell

Star-Shy Asteroids

Thanks to Gaia, many star positions (and proper motions) and minor planet positions (orbits) have improved so much that those of us who try to observe stellar occultations by minor planets have recently seen a vast improvement in our likelihood of success. These occultation events are an excellent way to discover minor planet satellites as well as double stars. At the very least, they provide highly accurate minor planet astrometric positions that lead to more accurate orbits, and if several observers record an event, the size and shape of the minor planet can be more accurately determined.

Perhaps surprisingly, a number of low-numbered (and thus generally larger) minor planets have never been observed to occult a star. Here are the ten lowest-numbered minor planets still awaiting their first-observed stellar occultation event.

To predict future stellar occultation events for any given minor planet (and so much more!), use the latest version of Occult – Occultation Prediction Software by David Herald.

Last Updated: February 24, 2025

180 Garumna
Main-belt Asteroid. Diameter 23.440 ± 0.414 km.
Rotation Period: 23.866 hours
Discovered 1878 Jan 29 by J. Perrotin at Toulouse.
Named for the Garonne river on which the city of discovery is situated. Garumna is the ancient name.
https://en.wikipedia.org/wiki/180_Garumna

183 Istria
Main-belt Asteroid. Diameter 32.927 ± 0.168 km.
Rotation Period: 11.77 hours
Discovered 1878 Feb 8 by J. Palisa at Pola.
Named for the {now Croatian} peninsula at the northern end of the Adriatic sea, containing Trieste and the city of discovery. Named by Vice-Admiral B. Freiherr von Wüllerstorf who was the commander of the first Austrian circumnavigatory adventure with the frigate Novara.
https://en.wikipedia.org/wiki/183_Istria

228 Agathe
Main-belt Asteroid. Diameter 9.30 ± 0.8 km.
Rotation Period: 6.484 hours
Discovered 1882 Aug 19 by J. Palisa at Vienna.
Named in honor of the youngest daughter of Theodor von Oppolzer (1841-1886), professor of astronomy in Vienna.
https://en.wikipedia.org/wiki/228_Agathe

244 Sita
Main-belt Asteroid. Diameter 11.077 ± 0.022 km.
Rotation Period: 129.51 hours
Discovered 1884 Oct 14 by J. Palisa at Vienna.
Named possibly for the wife of Rama in the Sanskrit epic The Ramayana. It is a symbol of the ideal spouse and of everlasting faith.
https://en.wikipedia.org/wiki/244_Sita

262 Valda
Main-belt Asteroid. Diameter 14.645 ± 0.141 km.
Rotation Period: 17.386 hours
Discovered 1886 Nov 3 by J. Palisa at Vienna.
Any reference of this name to a person or occurrence is unknown. Name proposed by the Baroness Bettina von Rothschild.
https://en.wikipedia.org/wiki/262_Valda

281 Lucretia
Main-belt Asteroid. Diameter 11.036 ± 0.145 km.
Rotation Period: 4.348 hours
Discovered 1888 Oct 31 by J. Palisa at Vienna.
Named in honor of Lucretia Caroline Herschel (1750-1848), sister of the discoverer (1781) of Uranus, Sir William Herschel (1738-1822), whom she assisted, beginning in 1772. She independently discovered seven or eight comets. After her brother’s death, she returned from England to Hannover, Germany and constructed a catalogue of the nebulae and clusters discovered by him. She received the Gold Medal of the Royal Astronomical Society in 1828.
https://en.wikipedia.org/wiki/281_Lucretia

291 Alice
Main-belt Asteroid. Diameter 10.456 ± 0.419 km.
Rotation Period: 4.313 hours
Discovered 1890 Apr 25 by J. Palisa at Vienna.
Name of unknown origin. Named by the Société Astronomique de France at the invitation of the discoverer. Independently discovered by A. Charlois at Nice one night later.
https://en.wikipedia.org/wiki/291_Alice

296 Phaëtusa
Main-belt Asteroid. Diameter 8.196 ± 0.100 km.
Rotation Period: 4.5385 hours
Discovered 1890 Aug 19 by A. Charlois at Nice.
Named for one of the daughters of Apollo and Klymene, changed by Zeus into poplars after the death of their brother Phaethon.
https://en.wikipedia.org/wiki/296_Pha%C3%ABtusa

299 Thora
Main-belt Asteroid. Diameter 15.757 ± 0.081 km.
Rotation Period: 272.9 hours
Discovered 1890 Oct 6 by J. Palisa at Vienna.
Named for the Norse god of thunder, weather, and crops.
Named by Geheimrat Prof. Scheibler in Berlin. In Norse mythology this name repeatedly exists as spouse of Helge, spouse of Ragnar Lodbrok, and as a girlfriend of Gudrun.
https://en.wikipedia.org/wiki/299_Thora

311 Claudia
Main-belt Asteroid. Diameter 26.300 ± 0.378 km.
Rotation Period: 7.532 hours
Discovered 1891 Jun 11 by A. Charlois at Nice.
The name was suggested to Charlois by the amateur astronomer Arthur Mee of Cardiff, Wales, to commemorate Mee’s wife, Claudia.
https://en.wikipedia.org/wiki/311_Claudia

References
Schmadel, Lutz D. 2012. Dictionary of Minor Planet Names. 6th ed. Berlin, Germany: Springer. https://doi.org/10.1007/978-3-642-29718-2.

Solar System Dynamics. (Downloaded 31 Jan 2025). (Small-Body Database Lookup). https://ssd.jpl.nasa.gov