Eclipse Comets

A total solar eclipse, such as that which will be crossing America on 21 Aug 2017, would present a great opportunity to discover a bright comet near the Sun.  Has that ever happened?  The answer is yes.

A comet, perhaps magnitude -4 or brighter, was spotted about 1.4° SW of the Sun during the total solar eclipse of 1 Nov 1948.  The editors of Sky & Telescope write in the January 1949 issue, “British Astronomical Association Circular No. 303, dated November 10, 1948, under the title, ‘The Eclipse Comet, 1948 I,’ reads in part:

There can be little doubt that the bright comet now reported seen in the southern morning sky is identical with the one seen during the eclipse of November 1.  The Times of November 2 in the report of the eclipse from its correspondent at Nairobi stated that a bright comet, with a long tail, was seen both by the crew of an R.A.F. aircraft and by observers on the ground.  The head, it was stated by one amateur astronomer, was still visible a few seconds after the Sun began to emerge.

A cable received by Dr. R. d’E. Atkinson, leading the Royal Observatory expedition, reports photographic confirmation of it, saying it was 93′ from the centre of the Sun in position angle 226°, and was very bright, with a tail.

“Harvard Announcement Card 956, dated November 22nd, reads in part:

Dr. Leland E. Cunningham, Students’ Observatory, University of California, Berkeley, writes: ‘New elements have been determined for the bright comet . . . .  These place the comet in position angle 228° and 104′ distant from the sun at the time of the total solar eclipse on November 1, which are in moderate agreement with Atkinson’s observed values of 226° and 93′, respectively.’

“Thus, although Comet 1948 I was missed by northern observers before it passed perihelion late in October, when its tail must have extended into the evening sky after sunset, the total eclipse of the sun provided a favorable opportunity to observe the comet practically a week before southern observers viewed it in their morning sky.  It well can be called the ‘eclipse comet’ of 1948.”

The editors of Sky & Telescope write in the March 1949 issue, “From The Observatory of December, 1948, we quote part of the proceedings of the meeting of the Royal Astronomical Society held on November 12th, at which Dr. R. d.’E Atkinson told something of his recent eclipse expedition to East Africa, and the discovery of the comet during the eclipse.  Dr. Atkinson said:

I propose to speak mainly about the comet which was observed during the eclipse; as far as our own eclipse observations are concerned, I believe they were successful, but the films have not yet been developed.

The comet, though very bright, was not visible at Mombasa, where we were (98% totality), but several newspaper reports from further north referred to it; they did not sound very convincing.  A photograph was published, but as printed it did not actually show the comet; the accompanying description was also based on an error, as I later learnt.  On the journey to Nairobi, sixty hours after the eclipse, I spoke to an eyewitness, whose account disagreed with that in the paper.  It was not until I had seen the photographs taken by the R.A.F. at Nairobi, and had found that they agreed with eye-witness reports at both places, that I realised it must have been a comet; I then made a very rough measurement of its place on the R.A.F. film, and telegraphed Dr. Merton.  As a result of my interest in these photographs, which were taken at 13,000 feet just within and just outside the shadow, the Air Commodore very kindly let me bring the films home for thorough examination.  [On one picture] very much enlarged from a hand-camera snapshot also taken by a member of the crew . . . the tail is clearly visible; visual observers all agreed that it extended downwards until it reached either clouds or the horizon, and it must have been twenty degrees long at least.  The visible part of it does not point away from the Sun at all; any portion which does this must have been extremely foreshortened.  [On another picture] the scale is larger and the definition much better, but the tail is too much underexposed to show except with a magnifying glass.  Viewed in this way, and accepting the idea that the root of the tail will point away from the Sun, one can see enough indications of curvature to make it seem that it is convex to the west; I therefore concluded in my cable a guess that the motion would be westwards, and this has proved correct.  The comet must certainly have been very bright; these pictures were taken with an aperture of f/5.6 and an exposure of 1/300 second; moreover, the head was visible for some 5-10 seconds after the end of totality.  It must certainly have been brighter than Venus.  I have now measured up three separate negatives, and they agree closely in giving a distance from the centre of the Sun of 105.4 minutes, and a position angle of 230°; however, there is some possibility of systematic error, and I have written to the Air Commodore to ask for further details.  If systematic errors can be eliminated, the place should, I think, be useful for orbit determination; it is a week earlier than any other place.”

Thus writes British astronomer Robert d’Escourt Atkinson (1898-1982) about comet C/1948 V1, the “Eclipse Comet of 1948” seen at Nairobi and Mombasa, Kenya on 1 Nov 1948.  It was next observed in the morning sky on 8 Nov 1948, and continued to be followed until 3 Apr 1949.

According to Edward S. Holden (1846-1914), John Martin Schaeberle (1853-1924) discovered a comet-like object on photographic plates taken during the 16 Apr 1893 total solar eclipse, but it has since been determined (Cliver 1989) that this was a coronal mass ejection (CME).

German-born British physicist Arthur Schuster (1851-1934) recorded a comet on photographic plates of the total solar eclipse of 17 May 1882 in Egypt.  The comet moved noticeably during the 1m50s of totality.  It is thought that this comet was a member of the Kreutz sungrazer group of comets.  It has received the designation of X/1882 K1.  The “X/” indicates that there were not enough observations of this comet to determine an orbit.  In fact, the only observations of this comet were during the total solar eclipse.  The comet is sometime called Comet Tewfik—named after the ruler of Egypt at that time in recognition of his hospitality towards the eclipse party.

A comet was discovered during the eclipse of 19 Jul 418 at Constantinople (Istanbul, Turkey) and was observed for four months afterwards.

Seneca the Younger (c. 4 BC – AD 65) writes in his Naturales quaestiones (Natural Questions):

Posidonius, in fact, tells us that during an eclipse of the Sun a comet once appeared which the sun’s proximity had hitherto concealed.

Did Posidonius (c. 135 BC – 51 BC) see this comet, or was he referring to an even earlier observation made by someone else?  With so much of the knowledge of the ancient world lost or destroyed by barbarians and zealots, we may never know.

Clarke, J. 1910, Physical science in the time of Nero; being a translation of    the Quaestiones naturales of Seneca
Cliver, E. W. 1989, Solar Physics, 122:2, 319-333
Federer, C. A. Jr., Sky & Telescope, January 1949, pp. 59-60
Federer, C. A. Jr., Sky & Telescope, March 1949, p. 110, 113
Hetherington, B. 1996, A Chronicle of Pre-Telescopic Astronomy
Kronk, G. W., Cometography, X/1882 K1 (Eclipse Comet or “Tewfik”)
Poitevin, P., Eclipse Comets
Seneca c. 65 AD, Naturales quaestiones, 7.20.4
Vaquero, J. M. 2014, Physics Today, 67:5, 9

Bonner Durchmusterung und Gaia

As our civilization and technology continue to evolve, it seems we take far too much for granted.  We neglect to consider how incredibly hard people used to work years ago to achieve results we today would pass off as almost trivial.  But history has many lessons to teach us, if only we would listen.

As an example, Prussian astronomer Friedrich Wilhelm August Argelander (1799-1875) at the age of 60 began publishing the most comprehensive star catalogue and atlas ever compiled, as of that date.  From 1852 to 1859, Argelander and his assistants carefully and accurately recorded the position and brightness of over 324,000 stars using a 3-inch (!) telescope in Bonn, Germany.  Employing the Earth’s rotation, star positions were measured as each star drifted across the eyepiece reticle in the stationary meridian telescope by carefully recording when each star crossed the line, and where along the line the crossing point was.

Stars Transiting in a Meridian Telescope

One person observed through the telescope and called off the star’s brightness as each star crossed the line, noting the exact position along the reticle on a pad with a cardboard template so that the numbers could be written down without looking away from the telescope.  A second person, the recorder, noted the exact time of reticle crossing and the brightness called out by the observer.  In this way, two people were able to record the position and brightness of every star.

Each star was observed at least twice so that any errors could be detected and corrected.  In some areas of the Milky Way, as many as 30 stars would cross the reticle each minute.  What stamina and dedication it must have taken Argelander and his staff to make over 700,000 observations in just seven years!  Argelander’s catalogue is called the Bonner Durchmusterung and is still used by astronomers even today.  It was the last major star catalogue to be produced without the aid of photography.

Like Argelander’s small meridian telescope, the European Space Agency’s Gaia astrometric space observatory is currently measuring tens of thousands of stars each minute (down to mv = 20) as they transit across a large CCD array—the modern day equivalent of an eyepiece reticle.  But instead of utilizing the Earth’s rotation period relative to the background stars of 23h56m04s, Gaia’s twin telescopes separated by exactly 106.5° sweep across the stars as Gaia rotates once every six hours.  A slight precession in Gaia’s orientation ensures that the field of view is shifted so that there is only a little overlap during the next six-hour rotation.

When Gaia completes its ongoing mission, it will have measured the positions, distances, and 3D space motions of around a billion stars, not just twice but 70 times!

Though electronic computers do most of the work these days, someone still has to program them.  Some 450 scientists and software experts are immersed in the challenging task of converting raw data into scientifically useful information.

I’d like to conclude this entry with a quotation from Albert Einstein (1879-1955), who was born and died exactly 80 years after Argelander.

Many times a day I realize how much of my outer and inner life is built upon the labors of my fellowmen, both living and dead, and how earnestly I must exert myself in order to give as much as I have received.

I love that quote.  Words to live by.

Wind in the Window

One very windy morning last week I lay in bed listening to the wind whistling in the window above me.  It was playing a pentatonic scale!  Albeit accompanied by some very complex and interesting overtones.  The pitches formed a major pentatonic scale: G♭4 – A♭4 – B♭4 – D♭5 – E♭5.

This led me to reflect on the origins of human music.  Even though there were no windows in prehistoric times, there has always been the sound of the wind amongst the rocks and the trees, and a myriad of other sounds in the natural world.  These sounds of nature must have provided the initial impetus for human music making, both vocal and instrumental.

Prime Meridians

The choice of the prime meridian (0° longitude) is, of course, completely arbitrary.  Here in the U.S., it is not uncommon to find 18th & 19th century maps and navigational aids showing the prime meridian going through Philadelphia or Washington, D.C.  In October 1884, the International Meridian Conference convened in Washington, D.C.  At that conference, 22 of 25 nations voted to make the longitude line through Greenwich, England the internationally recognized Prime Meridian (0° longitude). Santo Domingo voted against the resolution, and France and Brazil abstained.

Eugène Delporte and the Constellation Jigsaw

Belgian astronomer Eugène Joseph Delporte (1882-1955) discovered 66 asteroids from 1925 to 1942, but he is best remembered for determining the official boundaries of the 88 constellations, work he completed in 1928 and published in 1930.  The constellation boundaries have remained unchanged since then.

The International Astronomical Union (IAU), founded, incidentally, in Brussels, Belgium in 1919, established the number of constellations at 88—the same number, coincidentally, as the keys on a piano—in 1922 under the guidance of American astronomer Henry Norris Russell (1877-1957).  The IAU officially adopted Delporte’s constellation boundaries in 1928.

All the constellation boundaries lie along lines of constant right ascension and declination—as they existed in the year 1875. Why 1875 and not 1900, 1925, or 1930? American astronomer Benjamin Gould (1824-1896) had already drawn up southern constellation boundaries for epoch 1875, and Delporte built upon Gould’s earlier work.

As the direction of the Earth’s polar axis slowly changes due to precession, the constellation boundaries gradually tilt so that they no longer fall upon lines of constant right ascension and declination. Eventually, the tilt of the constellation boundaries will become large enough that the boundaries will probably be redefined to line up with the equatorial coordinate grid for some future epoch. When that happens, some borderline stars will move into an adjacent constellation. Even now, every year some stars change constellations because proper motion causes them to move across a constellation boundary. For faint stars, this happens frequently, but for bright stars such a constellation switch is exceedingly rare.

1892: First Auroral Photography

One hundred and twenty five years ago this month, on January 1, 1892, two Germans, astronomer & physicist Martin Brendel (1862-1939) and geographer & meteorologist Otto Baschin (1865-1933), arrived at Alta fjord near Bossekop in northern Norway to study the Northern Lights and conduct magnetic field measurements.  Their latitude was just shy of 70° N.  Brendel began photographing the aurora the next day, and his first extant photograph (the first ever) was taken on January 5, 1892.

Edward Emerson Barnard (1857-1923), incidentally, was to establish his reputation as an extraordinarily gifted astrophotographer later that same year when he began taking photographs of comets, clusters, nebulae (including galaxies), and the Milky Way using the 6-inch Crocker astrographic camera at the Lick Observatory.

The first extant photograph of the aurora, taken on January 5, 1892 by Martin Brendel
The first extant photograph of the aurora, taken on January 5, 1892 by Martin Brendel
Martin Brendel and his photograph of the aurora borealis on February 1, 1892 (below)
Martin Brendel and his photograph of the aurora borealis on February 1, 1892 (below)
Nordlichtdraperie - that's German for "northern lights curtains" - charming!
Nordlichtdraperie – that’s German for “northern lights curtains” – charming!

Otto Baschin (1865-1933)
Otto Baschin (1865-1933)

Catchers of the Light: A History of Astrophotography by Stefan Hughes