December 19 – Tau Ceti ‘e’ and ‘f’

Tau Ceti e and Tau Ceti f are as yet unconfirmed exoplanets orbiting, fairly obviously, the star Tau Ceti, a G-type main sequence star in the constellation Cetus (usually referred to as “the whale”, but actually a sea monster from Greek mythology). They are the fourth and fifth planets out from the star, and were discovered on December 19th, 2012, by the “radial velocity” method, the oldest known means of detecting planets outside our system.

Location of Tau Ceti

Location of Tau Ceti

Both planets are likely to be a fair bit bigger than the Earth (“f” could be up to seven times larger), but they have excited astronomers by being in the habitable zone of Tau Ceti. It is thought they could have temperatures of up to 50 or 60°C, which is plenty warm enough for the existence of life. Unfortunately for any Tau Cetians though, the parent star is known to have an extensive “debris disk”, meaning that any planets nearby would face a regular pounding by rocks of varying shapes and sizes, almost certainly including some big enough to cause serious problems for any fledgling species trying to evolve.

December 18 – Epimetheus

Saturn’s moon Epimetheus, discovered today in 1966 by Richard Walker, is a non-identical twin.  It, and its larger brother, Janus, which had been discovered three days previously by Audouin Dollfus, fly round Saturn in almost identical orbits (their mean orbital radii differ by a mere 50km or so).  Obviously, at the time of discovery, with only  the evidence of Earth-based telescopes to go by, this caused a certain amount of confusion among astronomers trying to work out where the supposed new single moon was.  At the time it was thought, also fairly obviously,  highly unlikely that two moons would share the same orbit without hitting each other.

Epimetheus from the Cassini Orbiter (image: NASA/JPL/SSI)

Epimetheus from the Cassini Orbiter (image: NASA/JPL/SSI)

It is possible that at some time in the past Epimetheus and Janus were part of a single larger body, but if that is the case it is likely to have been a very long time ago.  Both are heavily cratered, and their surface features display softening of their edges by the accumulation of dust, suggesting nothing much has changed there for some time.

Epimetheus was, in Greek mythology, a Titan (nowadays the name of a rather larger Saturnian moon), brother of Prometheus (also a moon of Saturn).  The pair were sons of Iapetus (another Saturnian satellite).  Epimethius was, according to some myths, married to Pandora (and guess what she gave her name to?).

Epithemius was given the job, shortly after the creation of the Earth, of finding a positive trait to give to each of the newly designed animals.  Unfortunately he ran out of good characteristics with one animal remaining, which you’ve probably already guessed was man.  That’s when Prometheus came along and gave  man the gift of fire, after which it all went downhill.

Epimetheus (3rd left) meets Pandora for the first time.

Epimetheus (3rd left) meets Pandora for the first time.

As it happens, though, they do share the orbit, and they don’t hit each other.  One moon does catch the other up every four years, but interactions between their gravities causes the inner moon to move faster (which causes it to move to a higher orbit) and the outer moon to slow down, causing its own orbit to drop a little.  So they actually exchange places, which is why I’m not going to call them the fifth and sixth moons, because they are each neither and both.

Launch, in 1958, of SCORE, the world’s first communications satellite (Signal Communications by Orbiting Relay Equipment).  The launch, from Cape Canaveral, was via an Atlas-B 10B rocket.

December 16 – Asteroid 351 Yrsa

Asteroid 351 Yrsa was discovered today in 1892 by Max Wolf.  There isn’t a great deal to say about it:  it’s in the main belt, and is about 40 km across.  It is thought to have been named after the wife of King Eadgils of Swedish legend.  her father, Helghe, who had only had a brief fling with her mother, visited the region where she lived years later and, not knowing she was his daughter, got her in the family way, as they say.   Unlike the average Greek god, who would have thought nothing of it, he did the decent thing and killed himself upon discovering the truth.

Lithograph depicting Yrsa

Lithograph depicting Yrsa

Max Wolf was a great friend of today’s birthday boy, Edward Emerson (E.E.Barnard, namesake of Barnard’s Star, one of the most closely observed objects in the Galaxy.  Barnard was mainly a prolific comet finder, discovering 17 in all (15 solo, and 2 co-discoveries), but he’s always going to be associated with the one star in my mind, because it was, and indeed may still be for all I know, the intended target of Project Daedelus, the mind-bogglingly ambitious unmanned interstellar mission proposed by the British Interplanetary Society.  When I was an impressionable teenager in the 1970’s, Daedelus seemed likely to happen “any year now”.  Unfortunately, 30 years later, they still haven’t quite got around to working out how to get the necessary helium-3 fuel back from Jupiter in order to get it to work, and I suspect that the cost in today’s money of a nuclear-powered spaceship bigger than a Saturn 5 and built in orbit would be rather more expensive than gold-plating the Isle of Wight or  buying Australia and Canada back.

E E Barnard

E E Barnard



December 15 – Janus

J R Hind discovered today’s main belt asteroid, 23 Thalia, from Hyde Park, London, on December 15th, 1852 (I’d like to see him try that nowadays). Thalia is an S-type asteroid of about 107 km diameter, located between the 3:1 and 5:2 Kirkwood gaps.

In Greek mythology, Thalia, daughter of Zeus and Mnemosyne, with a name derived from the verb “to flourish”, was the muse of comedy and pastoral poetry. She may or may not (depending on which source you believe) have been the mother of the Corybantes, attendants to the Great Mother of the Gods, and associated with particularly orgiastic rites.

We also have a moon today.  The discovery of Janus, one of the inner Saturnian satellites, is attributed to Audouin Dollfus, who first observed it on December 15th 1966. Three days later, Richard Walker also observed an object in the right place but at the wrong time, which caused confusion for a while, but was eventually found to be another moon, Epimetheus, which shares an orbit with Janus.

Janus, photographed by the Cassini probe (image credit: NASA / JPL / SSI)

Janus, photographed by the Cassini probe (image credit: NASA / JPL / SSI)

Janus is the two-faced Roman god of beginnings, entrances, gates, doors, etc. You should thank him the next time an automatic door opens for you. Janus is also one of the select group of deities after whom a month (January) is named, and strangely he has no Greek counterpart.

1965  –  launch of San Marco 1 by Italy. Being their first satellite, the Italians wisely did not fill it with lots of expensive equipment. It did, though, contain a couple of experiments to study the ionosphere, the layer of the atmosphere stretching from about 60 km to 1,000 km, a region you need to know about if you’re planning to become a space-faring nation, needing to send radio messages over great distances.

2000  –  Death of George Alcock, aged 88, hunter of novae and comets. I believe he found five of each (remarkable for south-eastern England), some of them from indoors using binoculars, and even occasionally through double glazing1!  His eyesight must have been unbelievable.

2014  –  Voyager 1 crossed the termination shock.


2015  –  Launch of Expedition 46 to the International Space Station.  This caused considerable press interest in my homeland (in fact I’m going to call it a frenzy) because in addition to Russian cosmonaut Yuri Malenchenko and American astronaut Tim Kopra, the three-man crew contained Tim Peake, the first Briton to float into the ISS (I was going to say “set foot aboard” the ISS, but I’ve seen the footage, and feet don’t feature much).  Because of the  numbering system they use at the ISS when crews overlap, these three also formed part of Expedition 47.

ISS Expedition 46 Patch

ISS Expedition 46 Patch

As a supporter of Port Vale FC, I was distraught to discover that one of Tim Peake’s tasks whilst on this mission was to unveil a flag featuring the name of our local rivals, Stoke City.  I’ve gone off him a little.


1   Journal of the British Astronomical Association, vol.111, no.2, p.64-66

December 14 – Tycho Brahe

Tycho Brahe was born today in 1546 in Denmark. As the child of a wealthy family (he was born in a castle) he was well placed to receive a good education, and took up astronomy while studying law.

Tycho Brahe wearing the Order of the Elephant (and the Moustache of the Walrus)

Tycho Brahe wearing the Order of the Elephant (and the Moustache of the Walrus)

Tycho made several leaps of the imagination, including the development of his own model of the solar system, which he nearly got right. He correctly deduced that the Moon orbits the Earth, and that the planets orbit the Sun. unfortunately he also decided that the Sun must orbit the earth; an easy mistake to make I suppose at that time, if you spend your entire life seeing it cross the sky thousands of times in front of your very eyes.

Tycho was also the first person to decide that novae (they weren’t called that at the time) originated further away than the Moon. The popular view was that the stars were fixed and unchanging, and anything that appeared in the sky had  to be closer than them. But Tycho noticed that a bright new star in Cassiopeia (now called SN1572) did not move against the background stars, and so must be farther away than all the objects that did. It sounds fairly reasonable to us, but in the 16th century the night sky was anything but obvious.

2009 – Launch of the Wide-field Infrared Survey Explorer (WISE) by NASA, on a mission  to map 99% of the sky. So far, it has found more than 33,000 asteroids and comets, over 200 Near-Earth Asteroids (including 43 potentially hazardous ones), the most luminous galaxy in the known universe, and numerous brown dwarfs.

2013  –  the Chinese Chang’E 3 mission lands on the Moon.

The Chang'E Lunar Lander, imaged by the Yutu rover (image: China National Space Administration)

The Chang’E Lunar Lander, imaged by the Yutu rover (image: China National Space Administration)



December 12 – Uhuru

Uhuru, also known as the X-Ray Explorer Satellite or SAS-1 (for Small Astronomical Satellite) was an orbiting observatory, specifically for X-ray astronomy (the first of its kind). It was launched from the Italian San Marco offshore launch platform off the coast of Kenya on December 12th 1970, Kenyan independence day, hence the post-launch choice of a new name, which, as all good Star Trek fans know, is the Swahili for “freedom”. Its three year mission was to seek out new X-ray sources via a survey of the entire sky.

Uhuru (image credit: NASA)

Uhuru (image credit: NASA)

Uhuru was the first US satellite to be launched by another country.  Under the terms of a memorandum of understanding between NASA and the University of Rome, the Americans provided the rocket and satellite, while the Italians were responsible for the assembly and launch (following training with NASA in Virginia). The site was chosen principally to enable easier access to an equatorial orbit than would be possible from Cape Canaveral (which would have needed a much larger rocket).

The joint mission was very successful, with Uhuru producing a catalog of some 300 X-ray objects during its three years, mostly binary systems and supernova remnants.

On a completely unrelated topic that has nothing at all to do with astronomy or spaceflight, but might appeal to Star Trek fans of a certain vintage, December 12 1970 is also notable in Twin Peaks circles, as it marks the birthday of Mädchen Amick (Shelley Johnson).

December 10 – Asteroid 211 Isolda

Asteroid 211 Isolda, discovered on December 10th 1879 by Johann Palisa, is about as average as asteroids get.  It’s dark, in the main belt, C-type, 150-ish km across, and has an orbital period of 5.3 years.

So today, as well as mentioning those orbital characteristics of Isolda with which we all should now be familiar from previous posts (aphelion – 3.53 AU; perihelion – 2.54 AU; semi-major axis – 3.04 AU, and longitude of ascending node – 263.8°) I’m going to say that Isolda has an eccentricity of about 0.16.

Eccentricity is another fairly simple concept: it’s got very little to do with the behaviour of the English upper classes (you shouldn’t confuse eccentricity with lunacy) but a lot to do with the orbit of almost everything in the solar system being non-circular.  Eccentricity, if we’re talking about planets, moons, asteroids and most known comets, will be measured on a scale somewhere between zero (completely circular) and one (an “escape” orbit).  Planets have a fairly low eccentricities (Earth = about 0.017); asteroids are a bit more wayward (their average is ten times greater, at 0.17), and comets can be anything, with values near to, or even in excess of, 1.0 (eccentricities of more than 1 are reserved for comets that are being flung out of the solar system following their solar fly-by).  Neptune’s moon Triton has the lowest known eccentricity, at 0.000016.  This is about as circular as can be accurately measured.

Isolda, of course, is named after Isolde, (or Iseult of Ireland) the lover of Sir Tristan of Arthurian legend and Wagnerian opera.

Tristan and Isolde

Tristan and Isolde

Today’s photograph shows husband and wife team Ludwig and Malvina Schnorr von Carolsfeld, Wagner’s original 1865 Tristan and Isolde.  Ludwig was a heldentonor, the dramatic tenor typical of Wagnerian  protagonists. Soprano Malvina was the daughter of the Portuguese consul in Copenhagen, and was a great-grand-neice of David Garrick, giant of the English theatre.

1999  ⇒  Launch of ESA’s XMM-Newton (it stands for X-ray Multi Mirror Mission), the largest satellite to date to be launched by the European Space Agency (4 tonnes in weight and 10 meters long).

December 09 – Patrick Moore

There’s not a lot I can say that hasn’t already been said a hundred times or more about this chap, but it’s four years today since the passing, at the age of 89, of Sir Patrick Alfred Caldwell-Moore CBE, FRS, FRAS, singleton, leg spinner, xylophonist (if that’s the right word), RAF veteran, composer, cat lover, EEC hater, star of The GoodiesThe Morecambe and Wise Show and GamesMaster, general legend, and best all-round entertainer since Daffy Duck.  And it appears from the photograph that he also may have owned a telescope.

Patrick Moore (image credit: unknown).

Patrick Moore (image credit: unknown).

I’m not sure where I got that signed photograph from, but it lives inside my copy of Mrs Moore in Space, by Patrick’s mother, Gertrude.

I briefly met him a few times, donkey’s years ago: two of these were at speeches he was giving in the environs of North Staffordshire and South Cheshire, where I was restricted to standing in line waiting for an autograph, and twice were a little more informal at book signings I was involved with in my previous life as a bookseller.  I’d like to say how many books Patrick Moore wrote, but I’m not entirely sure they can be easily counted, as they stretch over such a long period, and had such wildly varied life spans.

To end on a sour note: it’s pantomime season, so boos and hisses to Macmillan publishers, who decided in 2016 to cease publication of “Patrick Moore’s Yearbook of Astronomy”.  Remind me to never buy any of their books again.

1892  ⇒  Discovery of the large main belt asteroid 349 Dembowska by French astronomer Auguste Charlois.  It was named in honour of the Italian astronomer Baron Ercole Dembowski, a specialist in double stars (and if the name sounds less than Italian, it’s because his father was a Polish general).  349 Dembowska is about 140 km wide, and is one of the brightest of the large asteroids.  It is classified as R-type, characterised by spectral lines showing the presence of olivine and pyroxene (the main constituents of the Earth’s mantle), and possibly plagioclase feldspars.


December 08 – Asteroid 5 Astraea

Asteroid 5 Astraea was discovered on this day in 1845 by Karl Ludwig Henke, and, as it was still relatively unusual to find asteroids at that time, it won him an annual pension of 1200 Marks from the king. Astraea is S-type, in the main belt, is quite big (roughly 167 km across at its widest point) and takes just over 4 years to orbit the Sun.

In Greek mythology, Astraea is the celestial virgin, and her name means just that (“star maiden”). She was a personification of justice, innocence and purity, and was the last of the immortals to live down here among us humans. Upon leaving Earth she became the constellation Virgo.


Yesterday we met the concept of the semi-major axis, and if you were paying attention you will know what I mean when I say that Astraea’s is 2.57 AU.  Today I’m attacking you with another position-related phrase, the longitude of the ascending node.  Like yesterday’s, it sounds more complicated than it is.  But unlike yesterday’s, it needs a really long rambling explanation, so here goes.

It’s an unwieldy phrase, isn’t it? So I’ll break it down into small parts. Firstly, if I tell you that for Astraea it is 141.7°, you’ll already know that it’s some sort of direction.  Longitude, as you know, is a coordinate showing the east-west position of something.  It tells you how many degrees you have to turn in an anti-clockwise direction from some point of reference in order to end up pointing at the place you want to be.  For example, your directions might tell you that if you’re standing in the car park looking at the church (point of reference) you need to turn 141.7° to see the pub (or just follow the smell of the beer).

Next, a node is the point at which an inclined (i.e. not horizontal) orbit crosses the horizontal plane on which your reference point lies.  For objects in the solar system we use the ecliptic(the plane marked out by the Sun’s apparent path across the sky) as the plane, and the First Point of Aries (ask me later – just accept it as a direction in the sky) as the point of reference.  There will be two occasions in each orbit when a body such as Astraea crosses this plane: one when it goes down below it, and another when it comes back above it. This second one is the ascending node.

So, the longitude of the ascending node is the direction you would need to be looking in order to see Astraea, if you knew precisely when it was about to start heading upwards above the ecliptic. Does that make sense?

A poem from Emerson to finish (“cap-a-pie” means from head to foot):


Each the herald is who wrote
His rank, and quartered his own coat.
There is no king nor sovereign state
That can fix a hero’s rate;
Each to all is vulnerable,
Cap-a-pie invulnerable,
Until he write, where all eyes rest,
Slave or master on his breast,

I saw men go up and down,
In the country and the town,
With this tablet on their neck,—
‘Judgement and a judge we seek.’
Not to monarchs they repair,
Nor to learned jurist’s chair;
But they hurry to their peers,
To their kinsfolk and their dears;
Louder than with speech they pray,—
‘What am I? companion, say.’
And the friend not hesitates
To assign just place and mates;
Answers not in word or letter,
Yet is understood the better;
Each to each a looking-glass,
Reflects his figure that doth pass.
Every wayfarer he meets
What himself declared repeats,
What himself confessed records,
Sentences him in his words;
The form is his own corporal form,
And his thought the penal worm.

Yet shine forever virgin minds,
Loved by stars and the purest winds,
Which, o’er passion throned sedate,
Have not hazarded their state;
Disconcert the searching spy,
Rendering to a curious eye
The durance of a granite ledge
To those who gaze from the sea’s edge.
It is there for benefit;
It is there for purging light;
There for purifying storms;
And its depths reflect all forms;
It cannot parley with the mean,—
Pure by impure is not seen.
For there’s no sequestered grot,
Lone mountain tarn, or isle forgot,
But Justice, journeying in the sphere,
Daily stoops to harbour there.

Ralph Waldo Emerson (1847)

1842    Birth of Alphonse Louis Nicolas Borrelly, the French astronomer who crops up in these pages every few weeks as a discoverer of asteroids.  He found 18 in all, and discovered or co-discovered six comets.


December 07 – Asteroid 423 Diotima

Asteroid 423 Diotima was discovered from Nice by Auguste Charlois on December 7th 1898. It’s in the main belt, is a C-type, is fairly large (approximately 170 by 140 km) and rotates about every 4.8 hours.

Diptima has a semi-major axis of a little over 3 AU.  Semi-major axis is a new phrase to these pages, but don’t panic: it’s just the longest radius of of an elliptical orbit.

Diotima of Mantinea

Diotima of Mantinea

Diotima was named, by the Astronomisches Rechen-Institut, after one of Socrates’ teachers, Diotima of Mantinea (if she ever existed – the jury is still out on whether or not she was simply a creation of Plato). It is from the teachings of Diotima that we get the concept of platonic love. I can’t help thinking there’s a clue to her existence (or lack of it) in that name. Surely it would have been diotimic love?