Remembering Comet Holmes

Twelve years ago today, Comet Holmes (17P) brightened from magnitude 16.5 to 2.6, forming a right triangle with Mirfak (α Persei) and δ Persei, opposite to Algol. Here is what I wrote in The Sky This Week at that time.

TSTW 10/25/07

Comet Holmes Bursts on the Scene!

Who ever said astronomy isn’t exciting? Sure, much of what we observe in the cosmos seems predictable and unchanging—but then something unexpected happens and we are scrambling to get a front-row seat and our lives are thrown into an exhilarating tizzy for a few hours or days. Whether it be an unexpected auroral display, a meteor fireball, a nova, supernova, or comet, the result is the same: it is exciting to be an astronomer, to be attuned to a universe that existed long before we were born and that will be here long after we are gone. That, to me, is comforting.

Very early Wednesday, October 24, a 16th-magnitude short-period comet presently in Perseus by the name of Holmes brightened about 14 magnitudes from 16.5 to 2.6 in little more than 12 hours: a brightness increase of 363,000 times! While such a cometary outburst was unexpected, it is not unprecedented. From time to time, solar heating (greatest when a comet is near perihelion) must cause pressure to build up inside a comet as subsurface ices volatilize. Eventually, the pressure builds up until it explodes through the surface of the comet, spewing gas and dust into space and exposing fresh material to solar radiation. Sometimes, this process is so violent that the comet breaks into multiple fragments.

Comet Holmes (17P) is one of the so-called “short period” comets, meaning it orbits the Sun in less than 200 years or has been observed at more than one perihelion passage. Comet Holmes orbits the Sun every 6.9 years, ranging from just inside the main part of the asteroid belt (2.1 AU) to the orbit of Jupiter (5.2 AU). No doubt Comet Holmes’ original orbit has been substantially altered by the gravitational influence of Jupiter. Comet Holmes is presently 2.5 AU from the Sun (230 million miles) and 1.6 AU from the Earth (150 million miles), having just passed perihelion on May 4, 2007.

Comet Holmes was discovered during its last outburst, which occurred on November 6, 1892 by English amateur astronomer Edwin Holmes (1839-1919). It was observed again in 1906, but was then lost until being recovered in 1964. It has since been observed near perihelion at every return.

The recent outburst of Comet Holmes may be one for the record books. I am not aware of any other comet outburst being recorded where the comet brightened by as much as 14 magnitudes in less than a day! Fortunately, the first two nights after the outburst the sky was beautifully clear here. The first night, October 24, Comet Holmes looked like a star to the unaided eye. In binoculars, it looked like a tiny yellow or orange planetary nebula, only slightly bigger than a star, and of uniform brightness. The following night, October 25, it still looked like a star to the unaided eye, but in binoculars it was larger than the previous night. The total brightness had not diminished. In the telescope, the comet was truly spectacular, made all the more amazing considering how the comet was only 43° away from the closest full moon of the year! The round coma contained a bright off-center fan-shaped wedge with a brilliant tiny pointlike nucleus. There was definitely evidence of concentric, spiraling shells of material opening outward from the center of the coma to the outermost parts of the coma.

You have just got to get out to see this comet! And as often as possible! Here is an ephemeris for Dodgeville for the coming week.

TSTW 11/1/07

Comet Holmes (17P)

Comet Holmes slowly moves towards Mirfak this week, an impressive binocular and telescopic object in Perseus. It is easily visible to the unaided eye, too, as a small fuzzball on the Capella-side of Perseus.

Sunlight and solar wind particles are hitting the comet on the north-northeast side, and photographs show the comet is sharp edged there. The opposite, south-southwest side is ragged, with ionized gas streamers spreading out in that direction in long-exposure photographs.

Whatever tail the comet has is pretty much hidden behind it, as our viewing angle (known as the phase angle) diminishes from 15° to 13° this week. The phase angle is the Sun – Comet – Earth angle. A phase angle of 0° would mean we are looking directly down the tail (least favorable, maximum foreshortening). A phase angle of 90° would mean we are looking perpendicular to the tail (most favorable, no foreshortening).

Prime time for observing the comet is pretty much all night, with the comet transiting the celestial meridian at 2:05 a.m. CDT at the beginning of the week, and at 12:30 a.m. CST by the end of the week. Look at it every clear night, because surprising changes can and do occur. Don’t miss it! It may be a while until something like this happens again. The last time Comet Holmes went into a major outburst was 115 years ago!

Streetlighting Concerns

I submitted the following letter to the editor to the Dodgeville Chronicle this evening:

Dear Editor:

Have you noticed the gradual transformation of our streetlights in Dodgeville, Mineral Point, and other communities in SW Wisconsin?  The light source in our streetlights is changing.  High Pressure Sodium (HPS), which has been in use for decades and produces a orangish-white light, is being replaced by light emitting diodes (LEDs), producing a whiter light.

What’s not to like?  LED’s many advantages include: efficiency, longevity, instant-on and instant-off, and dimmability, to name a few.  But Alliant Energy is installing new streetlights that produce white light that is too blue, and the illumination levels are about 2.6 times as bright as the high pressure sodium streetlights they are replacing.

Lighting specialists use a term called “correlated color temperature” or CCT (in Kelvin) that allows us to compare the relative “warmness” (redder) or “coolness” (bluer) of  various light sources.   The illumination provided by candlelight has a CCT around 1500 K, HPS around 2000 K, an incandescent light bulb around 2800 K, sunrise/sunset around 3200 K, moonlight around 4700 K, and sunny noon daylight around 5500 K.  The higher the color temperature, the bluer the light.

Higher color temperature illumination is acceptable in workplace environments during the daylight hours, but lower color temperature lighting should be used during the evening and at night.  Blue-rich light at night interferes with our circadian rhythm by suppressing melatonin production, thus reducing sleep quality, and several medical studies have shown that blue light at night increases the risk of developing cancer, most notably breast cancer.  Even low levels of blue-rich light at night can cause harm.  While it is true that something as natural as moonlight is quite blue (4700K), even the light of a full moon provides an illumination level of just 0.01 foot-candle, far dimmer than street lighting, parking lot lighting, and indoor lighting we use at night.

LED streetlights are available in 2700K, 3000K, 4000K, and 5000K.  I believe that Alliant is installing 4000K streetlights in our area—I certainly hope they are not installing any 5000K.  What they should be installing is 2700K or 3000K.  These warmer color temperature lights are no more expensive than their blue-white counterparts, and the slightly higher efficiency of the blue-white LEDs is entirely nullified by over-illumination.

Even considering a modest lowering of light level with age (lumen and dirt depreciation), these new LED streetlights are considerably brighter than the HPS lights they are replacing.  Just take a look around town.  What is the justification for higher light levels in our residential areas, and when was there an opportunity for public input?  In comparison to older streetlights, the new LED streetlights direct more of their light toward the ground and less sideways or directly up into the night sky, and that is a good thing.  But now the illumination level is too high and needs to be reduced a little.

If you share my concerns about blue-rich lighting and illumination levels that are often higher than they need to be, I encourage you to contact me at oesper at mac dot com.  I operated an outdoor lighting sales & consulting business out of my home (Outdoor Lighting Associates, Inc.) from 1994-2005, and wrote the first draft of the Ames, Iowa Outdoor Lighting Code which was unanimously adopted by the city council in 1999, so I am eager to work with others in the Dodgeville area who are also interested in environmentally-friendly outdoor lighting.

David Oesper

Orion’s Throwing Stones!

Monday evening, October 21st, and Tuesday morning, October 22nd, will be the best time to watch the Orionid meteor shower, one of the year’s best meteor showers.

Up to two dozen meteors per hour might be seen between the hours of 3:00 a.m. and 5:00 a.m. or so— provided you can keep the 40%-lit waning crescent moon out of your field of view.

When to Watch:

10:16 p.m. Monday, October 21 through 12:19 a.m. Tuesday, October 22 (radiant rise in the ENE to moonrise)*

12:19 a.m. through 5:47 a.m. Tuesday, October 22 (moonlight will interfere; radiant will be highest in the sky at 5:18 a.m., and morning twilight begins at 5:47 a.m.)

Where to Be: In a rural area with no terrestrial lights visible that are brighter than the brightest star. Preferably no light domes (uncivil twilight) of cities or towns should be visible in the direction you will be looking.

What to Do: Dress for a temperature 20° F cooler than the actual air temperature. Bring a lawn chair and a warm sleeping bag or blankets. Try blocking the Moon with a building, hill, or trees— or use a strategically-placed black umbrella.

Where to Look: Generally look towards the radiant which is between Betelgeuse and the “feet” of Gemini.

What You’ll See: Fast meteors, many leaving persistent trains.

Meteor showers occur each year when the Earth in her orbit intersects the debris trail of a comet, and the comet that causes the Orionids is very famous, indeed. Halley’s Comet!

* Times listed are for Dodgeville, Wisconsin

Cell Phone Fiasco

I am one of the holdouts who really has no interest in carrying around a smartphone everywhere I go. I spend most of my day in front of a computer screen, get far too many emails to keep up with, and have even less time for social media. I treasure the precious little time I have to be “unplugged” and do not want my treasured (and increasingly rare) face-to-face interactions to be interrupted by technology—nor do I want to be distracted by it.

To me, a screen is to be viewed, not touched. I much prefer a physical keyboard, and web browsing on a large screen. I hate all the pop-up ads on a smartphone browser, and all the places you go to accidentally while swiping to scroll.

For several years, I have had a great basic cellular phone with a slide-out keyboard, the LG Cosmos 3.

The LG Cosmos 3 – A Basic Phone with Slide-Out Keyboard

I do more texting than phoning, so this phone works great for that, and it is smaller than a smartphone. Recently, the charging port on my LG Cosmos 3 gave out and I could no longer charge the phone.

LG Cosmos 3 Charging Port
USB to Micro USB Charging Cable

There has got to be a better way to charge a phone like this that avoids all the wear and tear plugging and unplugging the micro USB plug into the phone. I first took the phone to a couple of phone repair shops in Madison, but they both said they could not fix or replace the port. I then took the phone to Verizon. Here’s what I found out:

  1. Verizon cannot fix the LG Cosmos 3 charging port.
  2. The LG Cosmos 3 is no longer available.
  3. The LG Cosmos 3 is a 3G device, and Verizon will be shutting that network down on 12/31/19 so even if the phone could be fixed, it won’t work after that date, nor will any other 3G device.
  4. No cell phone is currently available with a slide-out keyboard.

What?! No basic phone with a slide-out keyboard for texting? After spending several hours researching other cellular phone service providers and manufacturers, I discovered that no 4G/LTE phone with a slide-out keyboard exists. My only basic phone option was to go back to a flip phone where texting would require the multi-tap entry system on 12 keys. Slow and tedious, like it was on earlier generations of cell phones. This is progress?

After a second visit to the Verizon store, I decided to purchase the LG Exalt LTE flip phone. My very positive experience using the LG Cosmos 3 gave me a good reason to stick with LG. Though I like the LG Exalt LTE phone, texting is tedious. I really hope that LG will release an LTE version of the Cosmos 3. LG Cosmos 4, perhaps?

If you feel as I do that cell phone manufacturers like LG should once again offer a basic phone with a physical QWERTY keyboard, please sign this petition on

Radio Telescope in a Carpet

The lunar farside would be a splendid place to do radio astronomy. First, the cacophony of the Earth would be silenced by up to 2,160 miles of rock. Second, lacking an atmosphere, a radio telescope located on the lunar surface would be able to detect radio waves at frequencies that are absorbed or reflected back into space by the Earth’s ionosphere.

Radio waves below a frequency of 10 MHz (λ ≥ 30 m) cannot pass through the ionosphere to reach the Earth’s surface. The Earth’s atmosphere is variably opaque to radio waves in the frequency range of 10 MHz to 30 MHz (λ = 10 to 30 m), depending upon conditions. The Earth’s atmosphere is mostly transparent to frequencies between 30 MHz (10 m) and 22 GHz (1.4 cm).

Not surprisingly, electromagnetic radiation of a non-terrestrial origin having wavelengths longer than 10 meters has been little studied. If we look, we might discover new types of objects and phenomena.

The best part is the lunar radio telescope wouldn’t have to be a steerable parabolic dish, but instead could be a series of dipole antennas (simple metal rods or wires) imbedded into a plastic carpet that could easily be rolled out onto the lunar surface. This type of radio telescope is “steered” (pointed) electronically through phasing of the dipole elements.

Even though the ever-increasing number of lunar satellites should be communicating at wavelengths far shorter than 10 meters, care must be taken to minimize their impact (both communication and noise emissions) upon all lunar farside radio astronomy.

There’s a Meteor in My Image!

The night of August 16, 2019 UT, I was hoping to be the first person to record an occultation of a star by the asteroid 10373 MacRobert, named after Sky & Telescope senior editor Alan MacRobert. Alas, it was not to be, but I did receive a celestial consolation prize (or is that a constellation prize?) just as rare: a meteor! Here it is:

Kappa Cygnid recorded on 16 Aug 2019, 3:51:21.540 – 3:51:21.807 UT (0.267s, field size ~ 15′)

In the caption above, you’ll note that I stated this was a Kappa Cygnid meteor. How did I determine that?

The first step is to determine the direction the meteor traveled through the image. Since I have an equatorially-mounted telescope, north is always up and east is to the left, just like in the real sky. Using Bill Gray’s remarkable Guide planetarium software, which I always use when imaging at the telescope, I identified two stars (and their coordinates) very close to the path of the meteor across the field. The meteor flashed through the field so quickly that I am not able to determine whether the meteor was traveling from NNE to SSW or vice versa. But since I was imaging in Sagittarius, south of all the radiants active on that date, it is most likely that the meteor was traveling NNE to SSW. But, of course, it could have been a sporadic meteor coming from any direction, though as you will see, I think I can convincingly rule out that scenario.

The two stars very close to the meteor’s path were:

3UC 148-239423
α = 17h 56m 38.42s, δ = -16° 23′ 27.1″

3UC 147-243087
α = 17h 56m 31.96s, δ = -16° 30′ 40.0″

The right ascensions and declinations above are epoch of date.

Now, if this meteor came from a particular radiant, a great circle from the meteor shower radiant to either of the two stars (or the midpoint along the line connecting them) should be in the same direction as the direction between the two stars crossed by the meteor.

Meteor shower radiants drift from night to night as the Earth passes through the meteor stream due to its orbital motion around the Sun. We must find the radiant position for each meteor shower that was active on August 16, 2019 UT for that date.

Antihelion, South δ Aquariid, α Capricornid, and Piscis Austrinid meteor shower radiant drift
Source: International Meteor Organization,
Perseid meteor shower radiant drift
Source: International Meteor Organization,
Kappa Cygnid meteor shower radiant drift
Source: International Meteor Organization,

Looking at Table 6, Radiant positions during the year in α and δ, on p. 25 of the International Meteor Organization’s 2019 Meteor Shower Calendar, edited by edited Jürgen Rendtel, we find that four major meteor showers were active on August 16: the Antihelion source, which is active throughout the year (ANT), the Kappa Cygnids (KCG), the Perseids (PER), and the South Delta Aquariids (SDA). Though right ascension and declination for these radiants (presumably epoch of date) are not given specifically for August 16, we can interpolate the values given for August 15 and 20. Note that the right ascensions are given in degrees rather than in traditional hours, minutes, and seconds of time.

We are now ready to plug all these numbers into a SAS program I wrote that should help us identify the likely source of the meteor in the image.

The results show us that the Kappa Cygnids are the likely source of the meteor in the image, with a radiant that is located towards the NNE (15.8˚) from the “pointer stars” in our image, at a bearing that is just 3.7˚ different from their orientation.

Space Travel Under Constant 1g Acceleration

The basic principle behind every high-thrust interplanetary space probe is to accelerate briefly and then coast, following an elliptical, parabolic, or mildly hyperbolic solar trajectory to your destination, using gravity assists whenever possible. But this is very slow.

Imagine, for a moment, that we have a spacecraft that is capable of a constant 1g (“one gee” = 9.8 m/s2) acceleration. Your spacecraft accelerates for the first half of the journey, and then decelerates for the second half of the journey to allow an extended visit at your destination. A constant 1g acceleration would afford human occupants the comfort of an earthlike gravitational environment where you would not be weightless except during very brief periods during the mission. Granted such a rocket ship would require a tremendous source of power, far beyond what today’s chemical rockets can deliver, but the day will come—perhaps even in our lifetimes—when probes and people will routinely travel the solar system in just a few days. Journeys to the stars, however, will be much more difficult.

The key to tomorrow’s space propulsion systems will be fusion and, later, matter-antimatter annihilation. The fusion of hydrogen into helium provides energy E = 0.008 mc2. This may not seem like much energy, but when today’s technological hurdles are overcome, fusion reactors will produce far more energy in a manner far safer than today’s fission reactors. Matter-antimatter annihilation, on the other hand, completely converts mass into energy in the amount given by Einstein’s famous equation E = mc2. You cannot get any more energy than this out of any conceivable on-board power or propulsion system. Of course, no system is perfect, so there will be some losses that will reduce the efficiency of even the best fusion or matter-antimatter propulsion system by a few percent.

How long would it take to travel from Earth to the Moon or any of the planets in our solar system under constant 1g acceleration for the first half of the journey and constant 1g deceleration during the second half of the journey? Using the equations below, you can calculate this easily.

Keep in mind that under a constant 1g acceleration, your velocity quickly becomes so great that you can assume a straight-line trajectory from point a to point b anywhere in our solar system.

Maximum velocity is reached at the halfway point (when you stop accelerating and begin decelerating) and is given by

The energy per unit mass needed for the trip (one way) is then given by

How much fuel will you need for the journey?

hydrogen fusion into helium gives: Efusion = 0.008 mfuel c2

matter-antimatter annihilation gives: Eanti = mfuel c2

This assumes 100% of the fuel goes into propelling the spacecraft, but of course there will be energy losses and operational energy requirements which will require a greater amount of fuel than this. Moreover, we are here calculating the amount of fuel you’ll need for each kg of payload. We would need to use calculus to determine how much additional energy will be needed to accelerate the ever changing amount of fuel as well. The journey may well be analogous to the traveler not being able to carry enough water to survive crossing the desert on foot.

Now, let’s use the equations above for a journey to the nearest stars. There are currently 58 known stars within 15 light years. The nearest is the triple star system Alpha Centauri A & B and Proxima Centauri (4.3 ly), and the farthest is LHS 292 (14.9 ly).

I predict that interstellar travel will remain impractical until we figure out a way to harness the vacuum energy of spacetime itself. If we could extract energy from the medium through which we travel, we wouldn’t need to carry fuel onboard the spacecraft.

We already do something analogous to this when we perform a gravity assist maneuver. As the illustration below shows, the spacecraft “borrows” energy by infinitesimally slowing down the much more massive Jupiter in its orbit around the Sun and transferring that energy to the tiny spacecraft so that it speeds up and changes direction. When the spacecraft leaves the gravitational sphere of influence of Jupiter, it is traveling just as fast as it did when it entered it, but now the spacecraft is farther from the Sun and moving faster than it would have otherwise.


Of course, our spacecraft will be “in the middle of nowhere” traveling through interstellar space, but what if space itself has energy we can borrow?

Satellite, Meteor, and Aircraft Crossings 2019

Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but on October 4, 1957 another “species” of sky vermin made its debut: artificial satellites.  In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.

I’ve put together a video montage of satellites I serendipitously recorded between March 31, 2019 and July 12, 2019.  Many of the satellite crossings are moving across the fields as “dashes” because of the longer integration times I need to use for some of my asteroid occultation work. A table of these events is shown below the video. The range is the distance between observer and satellite at the time of observation.

Satellites in higher orbits take longer to cross the field. When possible, I’ve included graphs of brightness as a function of time for these slower-moving satellites after each individual video and corresponding table. When you watch the videos of geostationary satellites, you are actually seeing the rotation of the Earth as the line between you and the satellite sweeps across the stars as the Earth rotates!

Uncertain of identification
A tumbler with sun glints!
A high-amplitude tumbler! Satellite is no longer operational.

I caught one meteor on 4 Jan 2019 between 5:32:57 and 5:32:59 UT. Field location was UCAC4 419-017279. I’m pretty sure the meteor was a Quadrantid!

And two aircraft crossed my field: on 7 Dec 2018 1:40:05 – 1:40:13 UT (UCAC4 563-026131) and 26 Jun 2019 5:02:07 – 5:02:10 UT (UCAC4 291-144196).

And high energy particles (natural radioactivity or cosmic rays) “zing” my CCD/CMOS detector every once in a while. Here are a few examples: 5 Jan 2019 3:46:00 – 3:46:02 UT (UCAC4 473-001074); 20 Apr 2019 3:41:46 – 3:41:47 UT (UCAC4 501-062663); 30 Jun 2019 7:37:31 – 7:37:33 (UCAC4 354-179484) and 7:47:41 – 7:46:44 (TYC 6243-00130-1).

Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21

Asteroids: Take a Number

Italian monk, mathematician, and astronomer Giuseppe Piazzi (1746-1826) discovered an unexpected 8th magnitude object in Taurus near Mars and the Pleiades at around 8:00 p.m. on January 1, 1801 at his observatory in Palermo, Sicily. Thinking it a comet, he recorded the position of the object over several nights, until illness forced him to quit on February 11, just a few days after the object passed fairly close to Mars. By early May, the object was too close to the Sun in the western sky to observe, and Piazzi despaired of ever recovering the object. The now-famous 24-year-old German mathematician Carl Gauss (1777-1855) came to the rescue. Gauss used Piazzi’s positions to determine an orbit for Ceres (so named by Piazzi) and predicted from the scant data its future positions when it would once again be visible in the night sky. Ceres was recovered only a half-degree away from its predicted position by Hungarian astronomer Franz Xaver von Zach (1754-1832) on December 7, close to Denebola and not far from a close conjunction of the planets Jupiter and Saturn, and then confirmed after a long stretch of cloudy weather on December 31, 1801. The German amateur astronomer Heinrich Olbers (1758-1840) found Ceres at Bremen two days later on January 2, 1802. Olbers (of Olbers’ Paradox fame) discovered the second asteroid, Pallas, on March 28, 1802. Many, many more asteroids have been discovered since then. They are sequentially numbered, originally in order of their discovery date, but nowadays in order of their receiving a precise orbit determination.

Fast forward.

The names of asteroids 998 through 1002, discovered between August 6-15, 1923, have special significance.

998 Bodea – named in honor of German astronomer Johann Elert Bode (1747-1826), whose empirical relationship of the distances of the planets (Titius-Bode Law) indicated that there should be a planet between the orbits of Mars and Jupiter, touching off a massive search led by von Zach for a new planet.

999 Zachia – named in honor of Franz Xaver von Zach, who published Piazzi’s observations and recovered Ceres after Gauss’ predicted positions.

1000 Piazzia – named in honor of Giuseppe Piazzi, who discovered the first asteroid, 1 Ceres.

1001 Gaussia – named in honor of Carl Friedrich Gauss, who predicted the position of Ceres so it could be recovered.

1002 Olbersia – named in honor of Heinrich Olbers who was the second person to recover Ceres and the discoverer of the second asteroid, 2 Pallas (and 4 Vesta, by the way).

Fortunately, German astronomer Johann Daniel Titius (1729-1796) finally did get an asteroid named after him as well: 1998 Titius, discovered on February 24, 1938.

As of August 19, 2019, 796,422 minor planets (asteroids, trans-Neptunian objects, etc., but not including comets) have been discovered, but only 541,128 have orbits that are well-enough determined that they have been given a minor planet number. When a minor planet is first discovered, it is given a provisional designation based on the date of discovery. For example, 2019 PE3 was discovered during the first half of August 2019. After enough high-quality astrometric data has been collected to determine an accurate orbit, the minor planet is assigned a number. For example, minor planet 1996 TB1 was discovered by IOTA member George Viscome on October 5, 1996. It received a number, 35283, in 2000, and it received a name, Bradtimerson, earlier this year (2019). George submitted the name to the IAU after Brad Timerson, mentor and inspiration to many of the current crop of asteroid occultation observers, passed away on October 17, 2018. So we now have 35283 Bradtimerson.

The counts in the paragraph above show us that 67.9% of the minor planets that have been discovered have been assigned a number. Of these, only 21,922 (4.1%) have received a name.

Many asteroids have been given interesting or unusual names. Excluding the many fine individuals (real, not fictional) who have an asteroid named after them, here are a few of my favorites. There are a few here that are actually named after a person, but the minor planet name has a meaning beyond just the person’s name.

Remember, these are real places that will be visited someday. Oh, to be so lucky!

Lots of asteroids are awaiting names. Can you come up with some interesting, entertaining, or poetic ones? Give it a try, check this list or do a search here to make sure it is new, and then post a comment here and I’ll probably include your ideas in this article, giving you credit, of course. Be creative!

To get you in the spirit, here are a few names I’ve come up with:

  • Botanica
  • Distantia
  • Eternium
  • Gandalf
  • Luminaria
  • Morethanamote
  • Portentia
  • Symphonica

Have fun!

Cometary Tails

A comet’s ion/plasma/gas tail points directly away from the Sun. A comet’s dust tail deviates somewhat (and sometimes a lot) from this, falling behind the comet along its orbital path around the Sun.

For the best view of either tail, our line of sight should be perpendicular to the length of the tail. However, that seldom happens, and we are viewing the tails with some degree of foreshortening. The orientation of the gas tail is called the phase angle, and it is the Sun – comet – observer angle.

A phase angle of 0° indicates we are looking straight down the tail of the comet (maximum foreshortening) with the head being oriented closest to the observer.

A phase angle of 90° indicates that our line-of-sight to the comet is perpendicular to the Sun-comet line, so we are viewing the comet’s gas tail with no foreshortening.

A phase angle of 180° indicates that we are again looking straight down the gas tail of the comet (again, maximum foreshortening) only this time the tail is closer to the observer and the head further away. Of course, the only time this orientation could happen is when the comet is transiting the Sun, thus rendering it essentially unobservable.

Phase angles of 0 to 90° mean that the comet head is closer to the observer than the tail; angles of 90 – 180° mean that the comet’s tail is closer to the observer than the head.

Here’s a table showing the phase angle, and some other information, for currently-observable comets brighter than 15th magnitude as seen from Earth. The column labeled Elongation indicates the Sun – observer – comet angle. In other words, the angular separation between the Sun and the comet.

A comet that is farther from the Sun than the observer can never have a phase angle as great as 90°, but a comet that is closer to the Sun than the observer can. Looking at the diagram above and considering a comet in a circular orbit around the Sun (highly unlikely, I know, but bear with me) and closer to the Sun than the observer, the phase angle would be 90° when the comet is at greatest elongation.

Incidentally, comet designations that have a number followed by the letter “P” (such as 29P, 68P, and 260P) are periodic comets (more precisely described as short-period comets), defined to be comets with orbital periods of less than 200 years or that have been observed at more than one perihelion passage.