The spectral type classification scheme for stars is, among other things, a temperature sequence. A helpful mnemonic for remembering the sequence is Oh, Be A Fine Girl (Guy) Kiss Me Like This, Yes! The O stars have the highest surface temperatures, up to 56,000 K (100,000° F), while the Y infrared dwarfs (brown dwarfs) have surface temperatures as cool as 250 K (-10° F).
Here are the brightest representatives of each of these spectra classes readily visible from the northern hemisphere. Apparent visual magnitude (V-band) is given unless otherwise noted.
9.1.6 The metaphysical options …there appear to be basically six approaches to the issue of ultimate causation: namely Random Chance, Necessity, High Probability, Universality, Cosmological Natural Selection, and Design. We briefly consider these in turn. Option 1: Random Chance, signifying nothing. The initial conditions in the Universe just happened, and led to things being the way they are now, by pure chance. Probability does not apply. There is no further level of explanation that applies; searching for ‘ultimate causes’ has no meaning. This is certainly logically possible, but not satisfying as an explanation, as we obtain no unification of ideas or predictive power from this approach. Nevertheless some implicitly or explicitly hold this view. Option 2: Necessity. Things have to be the way they are; there is no other option. The features we see and the laws underlying them are demanded by the unity of the Universe: coherence and consistency require that things must be the way they are; the apparent alternatives are illusory. Only one kind of physics is self-consistent: all logically possible universes must obey the same physics. To really prove this would be a very powerful argument, potentially leading to a self-consistent and complete scientific view. But we can imagine alternative universes! —why are they excluded? Furthermore we run here into the problem that we have not succeeded in devising a fully self-consistent view of physics: neither the foundations of quantum physics nor of mathematics are on a really solid consistent basis. Until these issues are resolved, this line cannot be pursued to a successful conclusion. Option 3: High probability. Although the structure of the Universe appears very improbable, for physical reasons it is in fact highly probable. These arguments are only partially successful, even in their own terms. They run into problems if we consider the full set of possibilities: discussions proposing this kind of view actually implicitly or explicitly restrict the considered possibilities a priori, for otherwise it is not very likely the Universe will be as we see it. Besides, we do not have a proper measure to apply to the set of initial conditions, enabling us to assess these probabilities. Furthermore, application of probability arguments to the Universe itself is dubious, because the Universe is unique. Despite these problems, this approach has considerable support in the scientific community, for example it underlies the chaotic inflationary proposal. It attains its greatest power in the context of the assumption of universality: Option 4: Universality. This is the stand that “All that is possible, happens”: an ensemble of universes or of disjoint expanding universe domains is realized in reality, in which all possibilities occur. In its full version, the anthropic principle is realized in both its strong form (if all that is possible happens, then life must happen) and its weak form (life will only occur in some of the possibilities that are realized; these are picked out from the others by the WAP, viewed as a selection principle). There are four ways this has been pursued. 1: Spatial variation. The variety of expanding universe domains is realised in space through random initial conditions, as in chaotic inflation. While this provides a legitimate framework for application of probability, from the viewpoint of ultimate explanation it does not really succeed, for there is still then one unique Universe whose (random) initial conditions need explanation. Initial conditions might be globally statistically homogeneous, but also there could be global gradients in some physical quantities so that the Universe is not statistically homogeneous; and these conditions might be restricted to some domain that does not allow life. It is a partial implementation of the ensemble idea; insofar as it works, it is really a variant of the “high probability” idea mentioned above. If it was the more or less unique outcome of proven physics, then that would provide a good justification; but the physics underlying such proposals is not even uniquely defined, much less tested. Simply claiming a particular scalar field with some specific stated potential exists does not prove that it exists! 2: Time variation. The variety of expanding universe domains could be realised across time, in a universe that has many expansion phases (a Phoenix universe), whether this occurs globally or locally. Much the same comments apply as in the previous case. 3: Quantum Mechanical. It could occur through the existence of the Everett-Wheeler “many worlds” of quantum cosmology, where all possibilities occur through quantum branching. This is one of the few genuine alternatives proposed to the Copenhagen interpretation of quantum mechanics, which leads to the necessity of an observer, and so potentially to the Strong Anthropic interpretation considered above. The many-worlds proposal is controversial: it occurs in a variety of competing formulations, none of which has attained universal acceptance. The proposal does not provide a causal explanation for the particular events that actually occur: if we hold to it, we then have to still explain the properties of the particular history we observe (for example, why does our macroscopic universe have high symmetries when almost all the branchings will not?). And above all it is apparently untestable: there is no way to experimentally prove the existence of all those other branching universes, precisely because the theory gives the same observable predictions as the standard theory. 4: Completely disconnected. They could occur as completely disconnected universes: there really is an ensemble of universes in which all possibilities occur, without any connection with each other. A problem that arises then is, What determines what is possible? For example, what about the laws of logic themselves? Are they inviolable in considering all possibilities? We cannot answer, for we have no access to this multitude of postulated worlds. We explore this further below. In all these cases, major problems arise in relating this view to testability and so we have to query the meaningfulness of the proposals as scientific explanations. They all contradict Ockham’s razor: we “solve” one issue at the expense of envisaging an enormously more complex existential reality. Furthermore, they do not solve the ultimate question: Why does this ensemble of universes exist? One might suggest that ultimate explanation of such a reality is even more problematic than in the case of single universe. Nevertheless this approach has an internal logic of its own which some find compelling. Option 5: Cosmological Natural Selection. If a process of re-expansion after collapse to a black hole were properly established, it opens the way to the concept not merely of evolution of the Universe in the sense that its structure and contents develop in time, but in the sense that the Darwinian selection of expanding universe regions could take place, as proposed by Smolin. The idea is that there could be collapse to black holes followed by re-expansion, but with an alteration of the constants of physics through each transition, so that each time there is an expansion phase, the action of physics is a bit different. The crucial point then is that some values of the constants will lead to production of more black holes, while some will result in less. This allows for evolutionary selection favouring the expanding universe regions that produce more black holes (because of the favourable values of physical constants operative in those regions), for they will have more “daughter” expanding universe regions. Thus one can envisage natural selection favouring those physical constants that produce the maximum number of black holes. The problem here is twofold. First, the supposed ‘bounce’ mechanism has never been fully explicated. Second, it is not clear—assuming this proposed process can be explicated in detail—that the physics which maximizes black hole production is necessarily also the physics that favours the existence of life. If this argument could be made water-tight, this would become probably the most powerful of the multiverse proposals. Option 6: Purpose or Design. The symmetries and delicate balances we observe require an extraordinary coherence of conditions and cooperation of causes and effects, suggesting that in some sense they have been purposefully designed. That is, they give evidence of intention, both in the setting of the laws of physics and in the choice of boundary conditions for the Universe. This is the sort of view that underlies Judaeo-Christian theology. Unlike all the others, it introduces an element of meaning, of signifying something. In all the other options, life exists by accident; as a chance by-product of processes blindly at work. The prime disadvantage of this view, from the scientific viewpoint, is its lack of testable scientific consequences (“Because God exists, I predict that the density of matter in the Universe should be x and the fine structure constant should be y”). This is one of the reasons scientists generally try to avoid this approach. There will be some who will reject this possibility out of hand, as meaningless or as unworthy of consideration. However it is certainly logically possible. The modern version, consistent with all the scientific discussion preceding, would see some kind of purpose underlying the existence and specific nature of the laws of physics and the boundary conditions for the Universe, in such a way that life (and eventually humanity) would then come into existence through the operation of those laws, then leading to the development of specific classes of animals through the process of evolution as evidenced in the historical record. Given an acceptance of evolutionary development, it is precisely in the choice and implementation of particular physical laws and initial conditions, allowing such development, that the profound creative activity takes place; and this is where one might conceive of design taking place. [This is not the same as the view proposed by the ‘Intelligent Design’ movement. It does not propose that God tweaks the outcome of evolutionary processes.] However from the viewpoint of the physical sciences per se, there is no reason to accept this argument. Indeed from this viewpoint there is really no difference between design and chance, for they have not been shown to lead to different physical predictions.
A few comments.
1: Random chance. At first, this strikes one as intellectual laziness, but perhaps it is more a reflection of our own intellectual weakness. More on that in a moment.
2: Necessity. Our intellectual journey of discovery and greater understanding must continue, and it may eventually lead us to this conclusion. But not now.
3: High probability. How can we talk about probability when n = 1?
4: Universality. We can hypothesize the existence of other universes, yes, but if we have no way to observe or interact with them, how can we call this endeavor science? Furthermore, explaining the existence of multiple universes seems even more problematic that explaining the existence of a single universe—ours.
5: Cosmological Natural Selection. We do not know that black holes can create other universes, or that universes that contain life are more likely to have laws of physics that allow an abundance of black holes
6. Purpose of Design. The presupposition of design is not evidence of design. It is possible that scientific evidence of a creator or designer might be found in nature—such as an encoded message evincing purposeful intelligence in DNA or the cosmic microwave background—but to date no such evidence has been found. Even if evidence of a creator is forthcoming, how do we explain the existence of the creator?
I would now like to suggest a seventh option (possibly a variant of Ellis’s Option 1 Random Chance or Option 2 Necessity).
7. Indeterminate Due to Insufficient Intelligence. It is at least possible that there are aspects of reality and our origins that may be beyond what humans are currently capable of understanding. For some understanding of how this might be possible, we need look no further than the primates we are most closely related to, and other mammals. Is a chimpanzee self-aware? Can non-humans experience puzzlement? Are animals aware of their own mortality? Even if the answer to all these questions is “yes”1, there are clearly many things humans can do that no other animal is capable of. Why stop at humans? Isn’t it reasonable to assume that there is much that humans are cognitively incapable of?
Why do we humans develop remarkable technologies and yet fail dismally to eradicate poverty, war, and other violence? Why does the world have so many religions if they are not all imperfect and very human attempts to imbue our lives with meaning?
What is consciousness? Will we ever understand it? Can we extrapolate from our current intellectual capabilities to a complete understanding of our origins and the origins of the universe, or is something more needed that we currently cannot even envision?
“Sometimes attaining the deepest familiarity with a question is our best substitute for actually having the answer.” —Brian Greene, The Elegant Universe
“To ask what happens before the Big Bang is a bit like asking what happens on the surface of the earth one mile north of the North Pole. It’s a meaningless question.” —Stephen Hawking, Interview with Timothy Ferris, Pasadena, 1985
1 For more on the topic of the emotional and cognitive similarities between animals and humans, see “Mama’s Last Hug: Animal Emotions and What They Tell Us about Ourselves” by primatologist Frans de Waal, W. W. Norton & Company (2019). https://www.amazon.com/dp/B07DP6MM92 .
References G.F.R. Ellis, Issues in the Philosophy of Cosmology, Philosophy of Physics (Handbook of the Philosophy of Science), Ed. J. Butterfield and J. Earman (Elsevier, 2006), 1183-1285. [http://arxiv.org/abs/astro-ph/0602280]
If you’re an astronomy teacher that likes to put a trick question on an open book quiz or test once in a while to encourage your students to think more deeply, here’s a good one for you:
On average, what planet is closest to the Earth?
The correct answer is C. Mercury.
Huh? Venus comes closest to the Earth, doesn’t it? Yes, but there is a big difference between minimum distance and average distance. Let’s do some quick calculations to help us understand minimum distance first, and then we’ll discuss the more involved determination of average distance.
Here’s some easily-found data on the terrestrial planets:
I’ve intentionally left the last two columns of the table empty. We’ll come back to those in a moment. a is the semi-major axis of each planet’s orbit around the Sun, in astronomical units (AU). It is often taken that this is the planet’s average distance from the Sun, but that is strictly true only for a circular orbit.1e is the orbital eccentricity, which is a unitless number. The closer the value is to 0.0, the more circular the orbit. The closer the value is to 1.0, the more elliptical the orbit, with 1.0 being a parabola.
The two empty columns are for q the perihelion distance, and Q the aphelion distance. Perihelion occurs when the planet is closest to the Sun. Aphelion occurs when the planet is farthest from the Sun. How do we calculate the perihelion and aphelion distance? It’s easy.
Perihelion: q = a (1 – e)
Aphelion: q = a (1 + e)
Now, let’s fill in the rest of our table.
Ignoring, for a moment, each planet’s orbital eccentricity, we can calculate the “average” closest approach distance between any two planets by simply taking the difference in their semi-major axes. For Venus, it is 1.000 – 0.723 = 0.277 AU, and for Mars, it is 1.524 – 1.000 = 0.524 AU. We see that Venus comes closest to the Earth.
But, sometimes, Venus and Mars come even closer to the Earth than 0.277 AU and 0.524 AU, respectively. The minimum minimum distance between Venus and the Earth in conjunction should occur when Venus is at aphelion at the same time as Earth is at perihelion: 0.983 – 0.728 = 0.255 AU. The minimum minimum distance between Earth and Mars at opposition should occur when Mars is at perihelion and Earth is at aphelion: 1.382 – 1.017 = 0.365 AU. Mars does not ever come as close to the Earth as Venus does at every close approach.
The above assumes that all the terrestrial planets orbit in the same plane, which they do not. Mercury has an orbital inclination relative to the ecliptic of 7.004˚, Venus 3.395˚, Earth 0.000˚ (by definition), and Mars 1.848˚. Calculating the distances in 3D will change the values a little, but not by much.
Now let’s switch gears and find the average distance over time between Earth and the other terrestrial planets—a very different question. But we want to pick a time period to average over that is sufficiently long enough that each planet spends as much time on the opposite side of the Sun from us as it does on our side of the Sun. The time interval between successive conjunctions (in the case of Mercury and Venus) or oppositions (Mars) is called the synodic period and is calculated as follows:
P1 = 87.9691d = orbital period of Mercury
P2 = 224.701d = orbital period of Venus
P3 = 365.256d = orbital period of Earth
P4 = 686.971d = orbital period of Mars
S1 = (P1-1 – P3-1)-1 = synodic period of Mercury = 115.877d
S2 = (P2-1 – P3-1)-1 = synodic period of Venus = 583.924d
S4 = (P3-1 – P4-1)-1 = synodic period of Mars = 779.946d
I wrote a quick little SAS program to numerically determine that an interval of 9,387 days (25.7 years) would be a good choice, because
9387 / 115.877 = 81.0083, for Mercury
9387 / 583.924 = 16.0757, for Venus
9387 / 779.946 = 12.0354, for Mars
The U.S Naval Observatory provides a free computer program called the Multiyear Interactive Computer Almanac (MICA), so I was able to quickly generate a file for each planet, Mercury, Venus, and Mars, giving the Earth-to-planet distance for 9,387 days beginning 0h UT 1 May 2019 through 0h UT 10 Jan 2045. Here are the results:
As you can see, averaged over time, Mercury is the nearest planet to the Earth!
For a more mathematical treatment, see the article in the 12 Mar 2019 issue of Physics Today.
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
Jupiter – Saturn*
Saturn – Uranus*
Uranus – Neptune*
*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.
Semimajor Axis (a)
Orbital Eccentricity (e)
Orbital Period (P)
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.
I’ve never been a fan of daylight saving time. During the warmest months for stargazing and other astronomy activities, daylight saving time (DST) puts the end of twilight (and every other astronomical event) an hour later: near, at, or past bedtime for children and early-rising adults.
The last time we tinkered with DST in the U.S. was to extend it in 2007 to begin the second Sunday in March and end the first Sunday in November (previously it was the first Sunday in April to the last Sunday in October). We currently observe daylight saving time 65.4% of the year (almost ⅔) and standard time the remaining 34.6% of the year (a little over ⅓).
DST is a zero-sum game. Getting that extra hour the first weekend in November sure is nice, but we pay for it when we lose an hour the second weekend in March. For a few days in November, we feel like we’re sleeping in an extra hour, but for a few days in March, we feel like we’re getting up an hour earlier than usual.
While I would much prefer to stay on standard time all year long nationwide, there doesn’t appear to be much public support for that. On the other hand, there is a groundswell of support for going to year-round DST. Even this would be preferable to our current system, in my opinion.
We have toyed with the idea of year-round DST once before: from January 6, 1974 to October 27, 1974. During the winter months in early 1974, there was a lot of public outcry about schoolchildren going to school in the dark, and I’m sure the pre-sunrise cold was a factor, too. So, the year-round DST experiment was terminated early (it was supposed to last until April 27, 1975). Would it be any different this time around?
Northern states (where the winter nights are longest) would be most affected by year-round DST, as would areas in the far-western reaches of each of the time zones. Here in Wisconsin, we would see something like the following:
Some Highlights of Year-Round Daylight Saving Time in Wisconsin (times are for Dodgeville, WI)
Earliest End of Evening Twilight: 7:08 p.m. (around December 6)
Earliest Sunset: 5:26 p.m. (around December 9)
Latest Sunrise: 8:32 a.m. (around January 3)
Latest Onset of Morning Twilight: 6:50 a.m. (around January 6)
I have an idea. If we extend DST to year-round, why not also start the school day an hour later? There are studies that show that most students would benefit from a later start of the school day. Of course, that would also mean that many parents would probably want to start their work day an hour later, too. But if we do that, then what’s the point in going to year-round DST in the first place?
Many states are currently considering and some have even passed legislation extending DST to year-round, but federal law will have to change to allow any of these states to do this. Right now, states only have the right to opt out of DST altogether, as Arizona and Hawaii currently do.
The first requirement is the existence of laws of physics that guarantee the kind of regularities that can underlie the existence of life. These laws as we know them are based on variational and symmetry principles; we do not know if other kinds of laws could produce complexity. If the laws are in broad terms what we presently take them to be, the following inter alia need to be right, for life of the general kind we know to exist:
The neutron-proton mass differential must be highly constrained. If the neutron mass were just a little less than it is, proton decay could have taken place so that by now no atoms would be left at all.
Electron-proton charge equality is required to prevent massive electrostatic forces overwhelming the weaker electromagnetic forces that govern chemistry.
The strong nuclear force must be strong enough that stable nuclei exist; indeed complex matter exists only if the properties of the nuclear strong force lies in a tightly constrained domain relative to the electromagnetic force.
The chemistry on which the human body depends involves intricate folding and bonding patterns that would be destroyed if the fine structure constant (which controls the nature of chemical bonding) were a little bit different.
The number D of large spatial dimensions must be just 3 for complexity to exist.
It should not be too surprising that we find ourselves in a universe whose laws of physics are conducive to the existence of semi-intelligent life. After all, we are here. What we do not know—and will probably never know: Is this the only universe that exists? This is an important question, because if there are many universes with different laws of physics, our existence in one of them may be inevitable. If, on the other hand, this is the only universe, then the fantastic claims of the theists, or at least the deists, become more plausible.
You may wonder why I call the human race semi-intelligent. Rest assured, I am not being sarcastic or sardonic. I say “semi-intelligent” to call attention to humanity’s remarkable technological and scientific achievements while also noting our incredible ineptness at eradicating war, violence, greed, and poverty from the world. What is wrong with us?
References G.F.R. Ellis, Issues in the Philosophy of Cosmology, Philosophy of Physics (Handbook of the Philosophy of Science), Ed. J. Butterfield and J. Earman (Elsevier, 2006), 1183-1285. [http://arxiv.org/abs/astro-ph/0602280]
Did you know that it is possible to observe a meteor shower when its radiant is below your horizon? When its radiant is too far south (or north, in the southern hemisphere) to ever rise above your horizon? When its radiant is even located near the Sun?
Yes you can! By video recording the Earth-facing night side of the Moon, or during a total or partial lunar eclipse, you have the opportunity to record meteors impacting the surface of the Moon. Those of us who record occultations of stars by asteroids and trans-Neptunian objects already have the equipment necessary to accurately document such events, which typically produce brief flashes of light lasting for a few hundredths of a second.
Leonid meteor lunar impact flashes of +3m to +8m were recorded in 1999 and 2001, and Geminid meteor lunar impact flashes have been recorded that were between +5m and +9m. Meteor impact events have also been recorded during lunar eclipses, such as just after the beginning of the total lunar eclipse of January 20/21, 2019.
Besides during lunar eclipses, the best time to look for meteor impact events on the Moon is when most of the Earth-facing side of the Moon is dark and illuminated only by earthshine. This occurs during the waxing crescent and waning crescent phases.
NASA has twin 14-inch telescopes that observe the nighttime part of the Moon between the phases of New and First Quarter, and between Last Quarter and New. These telescopes have recorded 435 flashes on the Moon from 2005 to April 2018.
On Mt. Kyllini (930 m), Corinthia, Greece, the 1.2 m Kryoneri telescope of the National Observatory of Athens has been employed in a four year project called NELIOTA (Near-Earth Object Lunar Impacts and Optical Transients) to monitor the Moon for lunar flashes using a two camera system (one R-band and one near-IR) at a video rate of 30 frames per second. All candidate flashes are compared against a database of artificial satellites to exclude false positives due to sunglints of satellites passing in front of the Moon. Between February 2017 and January 2019, forty lunar impact events have been detected.
Of course, you’re more likely to capture a lunar meteor impact flash during a major meteor shower.
Peter Zimnikoval in Slovakia has written a wonderful program called MetShow that will present your local circumstances for the Moon at any date and time and for any meteor shower radiant. I’ve reproduced in the gallery below the lunar circumstances for all the major meteor showers (ZHR ≥ 10) for the remainder of 2019.
Not only does the lunar phase have to be favorable, but the meteor shower radiant must be coming from a direction that will impact a nighttime part of the Moon that we can see. If the Moon is located near the radiant of a meteor shower, then most of the meteors will impact the far side of the Moon where they will be unobservable from Earth. If the Moon is located near 180˚ from the meteor shower radiant, then the meteors will favor the near side.
This year, the best meteor showers to monitor are the Eta Aquariids around May 6, the Delta Aquariids around July 30, and the Ursids around December 23.
Most meteor showers have a broad maximum, so the exact time to observe the Moon is not as important. But if the meteor shower has a sharp peak, then one should consider the time offset between the Earth and the Moon. Peter Zimnikoval writes (personal communication, 2019):
“Bombarding of the Moon’s surface is almost the same as on the Earth. The position of the observed radiant is given as the vector sum of the heliocentric motion of the meteoroids and the Earth’s motion. For the Moon, there is only a small difference due to its orbital velocity (1 km/s). Regular meteor showers cross the Earth’s orbit at the same point every year. The angular position of this point is described as solar longitude (J2000). The Moon at 3rd quarter reaches this point about 3.6 hours before the Earth (384,399 km / 29.78 km/s = 12,908 seconds = 3.6 hours). The Moon at 1st quarter reaches this point about 3.6 hours after the Earth.”
“For most of the regular meteor showers (Perseids, Orionids, Geminids) this time shift is not very important. Their maxima are not too sharp and the duration is many hours. The time shift may be important for very narrow meteor streams, where the suspected time of maximum is only a few hours and therefore observed from only a small part of the Earth. When the structure of a shower is very sharp, then small differences in the position of the Earth and the Moon passing through this stream can make a difference. At full moon or new moon, the Moon may reach a higher density of particles than the Earth, but these phases are not suitable for observation of lunar impact flares.”
Liakos, Alexios et al.(2019). NELIOTA Lunar Impact Flash Detection and Event Validation. Proceedings of the “ESA NEO and Debris Detection Conference -Exploiting Synergies-“, held in ESA/ESOC, Darmstadt, Germany, 22-24 January 2019. arXiv:1901.11414 [astro-ph.EP].
Zimnikoval, Peter (2017). Lunar impact flashes. WGN, Journal of the International Meteor Organization, 45:5.
Humans typically can hear sound waves in the range 20 Hz to 20,000 Hz. Frequencies below 20 Hz are called infrasound and frequences above 20 kHz are called ultrasound. The speed of sound in dry air at a temperature of 20˚ C (68˚ F) and an atmospheric pressure of 1 bar (slightly less than the average air pressure at sea level) is 343 m/s. Dividing the speed of sound by the frequency (in Hz) gives us the wavelength of the sound waves: 17 m (56 ft.) at 20 Hz, and 17 mm (0.67 in.) at 20 kHz.
Meteoroids enter the Earth’s atmosphere (thus becoming meteors) at hypersonic velocities, 35 to 270 times the local speed of sound (Mach 35 to Mach 270). Only a small portion of the total energy of the incoming meteoroid is transformed into visible light: most of the energy dissipated goes into acoustic shock waves. If the meteoroid is on the order of a centimeter (0.4 inches) or larger, infrasound waves are generated that can be detected on the ground, albeit after a delay of many seconds to minutes.
Infrasound waves can travel long distances, but higher frequencies are attenuated due to spreading losses and absorption over much shorter distances. There are many natural and man-made sources of infrasound waves, so identifying an incoming meteoroid as the source of the infrasound requires that we also “see” and record the meteoroid optically (the “meteor”), through radar, or VLF radio emissions from the meteoroid’s ionization trail in the Earth’s atmosphere. Ideally, all of these methods should be used at each observing station to best characterize the size and kinetic energy of each incoming meteoroid.
Infrasound detectors are not yet an off-the-shelf commodity. Chapparal Physics (http://www.chaparralphysics.com) is one good source, but seeing as they do not list any prices you know the equipment will be expensive.
An infrasound detector is basically an extremely sensitive microphone that can detect tiny changes in air pressure. A peak sensitivity around 1 Hz is probably a good place to start for detecting meteors. Meteors large and/or energetic enough to be detected on the ground are rare, not even one a day for a given station, so automated recording will be necessary.
Finally, it is important to know that louder sounds that we cannot hear (infrasound and even ultrasound) can sometimes have adverse physical and psychological effects on humans. The cause can be as simple as a malfunctioning piece of mechanical or electrical equipment, or as nefarious as a sonic weapon. It would be advantageous to have a readily available and affordable infrasound and ultrasound detector to detect problem emissions.
For example, you might want an
Infrasound detector that maps 0.02 Hz – 20 Hz to the 20 Hz – 20 kHz audible range
Ultrasound detector that maps 20 kHz – 20 MHz to the 20 Hz – 20 kHz audible range
References Silber, Elizabeth A. (2018). Infrasound observations of bright meteors: the fundamentals. WGN, Journal of the International Meteor Organization, 46:2.
I’ll be 63 in a couple of months. My the years go fast, faster still of late.
Naturally, I’m beginning to look toward retirement when I can finally devote nearly all my time and energy to astronomy, preservation and restoration of our nighttime environment, and classical music. These three avocations have been my primary interests all of my adult life.
I’m in need of some retirement advice by someone who is not trying to sell me a financial product. I’d like to semi-retire as soon as possible, but want to wait until age 70 to collect Social Security when the monthly benefit reaches a maximum. So, I guess that means gradually cutting back work hours and supplementing the lost income with some retirement benefits.
I’m in a good position in terms of having a marketable work skill for the semi-retirement years. You’d be hard pressed to find a better SAS programmer. I’ll be at SAS Global Forum 2019 in Dallas this spring if you want to talk.
Honestly, I’ve been in a bit of a funk since I started this blog back in December 2016. First, Trump got elected, and that made me realize how bad things have gotten in this country. That someone so boorish and with zero job skills as a public servant got elected as President of the United States is both frightening and depressing. And the national nightmare continues. Then, last fall, my employer moved everyone except for management into an open office environment, which I hate. Throughout my work career, I’ve always had my own office or a cubicle and now I’m in a big open room with lots of distractions and a desk half the size of what I had just a few months ago, and no place to put my books, so I had to bring them all home. No one wants to learn SAS at my company anymore, even though I do amazing things with it every day. I’m in high demand, but they’re not hiring anybody anymore with SAS skills. That’s depressing, because it is a great language and a great company and SAS Institute most definitely continues to innovate. But open source is the name of the game where I work now.
It is easy to feel isolated living in a small town. As my friend Jeff Dilks once said when he was a physics teacher in Shenandoah, Iowa, the chances of finding anyone else in a small town (or rural area) with similar interests and abilities are vanishingly small if you have “big city” interests and a specialized education. That’s true, but where else are you going to live if you want to do observational astronomy and ride a bicycle to and from work? Quality of life issues like that, you know. But loneliness, yes, and I imagine that gets to be more of a challenge in our later years.
For something like 30 years, I’ve wanted to help develop and nurture a science-oriented and education-oriented intentional community where astronomy is a major focus. I even have a name for it: Mirador Astronomy Village. Can’t think of a better way to spend my retirement years, but it takes serious money to get something like this off the ground, and money I don’t have.
With open office and all (which is pretty much ubiquitous nowadays), I’ve soured on the idea of working for “Corporate America” any longer. I’d be much happier as a public servant, trying to make the world a better place and helping to solve the many problems for which Corporate America is not the answer, and has no answers.
The word desideratum has been a part of the English language since at least 1651, according to the Oxford English Dictionary, which provides this definition:
Something for which a desire or longing is felt; something wanting and required or desired.
This word comes from the Latin dēsīderātum “thing desired”, and its plural is desiderata.
The French astronomer Auguste Charlois (1864-1910) discovered the asteroid 344 Desiderata on 15 Nov 1892 at the Nice Observatory, in southeastern France near the border with Italy. Like most of his 99 asteroid discoveries between 1887 and 1904, it is named to honor a woman. In this case, that would be Désirée Clary (1777-1860), French woman who became Queen Desideriaof Sweden.
On 25 Feb 2019, I recorded 14.1-magnitude 344 Desiderata passing in front of the 14.6-magnitude star UCAC4 639-020401 in the constellation Auriga. Right before the event, star and asteroid formed a 13.6-magnitude blended image, and when the asteroid covered up the star, the brightness dipped 0.5 magnitude to the brightness of the asteroid alone. This great cover-up event lasted 16.8 seconds. Here’s a light curve of the event as a function of time.
That dip to the right (after) the asteroid covered up the star suggests that a smaller satellite of the asteroid might have also passed in front of the star. Alas, it is only noise. We can tell this by looking at the light curve of a nearby comparison star at the same time.
Here is the smoothed and fitted light curve of the asteroid occultation event.
Max Ehrmann (1872-1945) wrote a prose poem Desiderata (Latin: “things desired”) in 1927 that has since become well known, and for good reason.
Go placidly amid the noise and the haste, and remember what peace there may be in silence. As far as possible, without surrender, be on good terms with all persons.
Speak your truth quietly and clearly; and listen to others, even to the dull and the ignorant; they too have their story.
Avoid loud and aggressive persons; they are vexatious to the spirit. If you compare yourself with others, you may become vain or bitter, for always there will be greater and lesser persons than yourself.
Enjoy your achievements as well as your plans. Keep interested in your own career, however humble; it is a real possession in the changing fortunes of time.
Exercise caution in your business affairs, for the world is full of trickery. But let this not blind you to what virtue there is; many persons strive for high ideals, and everywhere life is full of heroism.
Be yourself. Especially do not feign affection. Neither be cynical about love; for in the face of all aridity and disenchantment, it is as perennial as the grass.
Take kindly the counsel of the years, gracefully surrendering the things of youth.
Nurture strength of spirit to shield you in sudden misfortune. But do not distress yourself with dark imaginings. Many fears are born of fatigue and loneliness.
Beyond a wholesome discipline, be gentle with yourself. You are a child of the universe no less than the trees and the stars; you have a right to be here.
And whether or not it is clear to you, no doubt the universe is unfolding as it should. Therefore be at peace with God, whatever you conceive Him to be. And whatever your labors and aspirations, in the noisy confusion of life, keep peace in your soul. With all its sham, drudgery and broken dreams, it is still a beautiful world. Be cheerful. Strive to be happy.