October 10 – Discovery of Neptune’s moon, Triton (1846)

Discovered on October 10th 1846 by William Lassell, (who was living and working at that time in West Derby, Liverpool), the Solar System’s biggest retrograde moon Triton, aka Neptune I, is, at 1,353 km radius (approx) the largest satellite of Neptune.

Triton from Voyager 2 (image: NASA)
Triton from Voyager 2 (image: NASA)

Lassell wasn’t daft.  The massive Neptune itself had only been discovered 17 days previously, so where else was he going to be looking for moons?

Current thinking is that Triton is a captured Kuiper Belt Object.  It has a thin atmosphere of mostly nitrogen, with a little methane mixed in, and is, like our own Moon, locked in a synchronous orbit, meaning it always keeps the same face pointing toward its parent (or possibly in this case “adoptive parent”).

Triton (image credit: NASA/JPL-Caltech)
Triton (image credit: NASA/JPL-Caltech)


1868  –  Discovery of asteroid 106 Dione by J C Watson.

1874  –  Discovery of asteroid 139 Juewa, also by J C Watson.

August 14 – Three new Neptunian Moons (2002)

Neptune’s moons Neso, Halimede and Sau were all discovered on this day, in 2002. As with Laomedeia (see yesterday’s post), they were all named after the Nereids of Greek mythology. Their discovery pushed the number of known Neptunian satellites up to 13, but it’s now at 14 with the spotting of Psamathe the following year.
Neso is abount 60 km in diameter, and is the outermost of Neptune’s irregular satellites. Neso is thought to be the remnant of a larger body.

Halimede is a grey moon, 62 km across, and possibly a remnant from a collision involving the moon Nereid.

Sau is smaller, at about 42 km in diameter, and has a very inclined orbit.

Neptune from Voyager 2 (image: NASA)

Unlike most recent moon discoveries, today’s trio were found using the combined resources of two Earth-based telescopes: the 4 metre Blanco in Chile, and the 3. 6 metre Canada-France-Hawaii telescope on Mauna Kea, Hawaii. And because their discoveries centred on following tiny specs of light across the sky, I won’t be including any photographs. Instead, today’s picture is one taken of Neptune by Voyager 2 (which missed out on finding these three moons), showing cirrus-like clouds high above the beautiful windy planet.

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Asteroid 111 Ate was discovered by C H F Peters on August 14th 1870. It is a main-belt asteroid, named after the Greek goddess of mischief and destruction. Being a Port Vale supporter I am familiar with her work. Ate is a C-type asteroid, and at an estimated 143 km in diameter, it is one of the larger.

August 13 – Discovery of Neptune’s moon Laomedeia (2002)

A very small moon of Neptune, Laomedeia, was discovered today in 2002 by a very large group of astronomers (so I won’t be naming them) using the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope and the Canada-France-Hawaii 3.6-m telescope on Mauna Kea. Laomedeia orbits the planet Neptune every 8.7 Earth years, and is a relatively tiny 42km in diameter (Neptune is about 49,000 km across). In Greek mythology, Laomedeia was one of the fifty Nereids. She is described, rather vaguely, by Hesiod as the “leader of the folk”. Make of that what you will.

Nereids mourning Achilles
Nereids mourning Achilles

I can’t find a representation of Laomedeia anywhere, but the black-figure hydria, above, shows nine of the Nereids, so there’s about an eighteen percent chance she’s in there somewhere.

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Physicist Anders Jonas Ångström was born today in 1814 in Lödgö, in the province of Medelpad, Sweden. A keen believer in the use of spectroscopy, he was the first person to examine the spectrum of the aurora borealis. He now gives his name to the unit of measurement of the wavelength of light, denoted by the letter Å.

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ALSO TODAY . . . .
1847 – Discovery of asteroid 7 Iris by J R Hind (his first). Iris is a very large S-type main belt asteroid, over 200 km wide in some directions, named after the goddess of the rainbow.
1861 – Discovery of asteroid 71 Niobe by (Karl Theodor) Robert Luther. Niobe is 83 km in diameter, and an S-type asteroid. It takes it’s name from the daughter of Tantalus in Greek mythology, who made the mistake of boasting about her fourteen children to the goddess Leto (who only had two). Some accounts say one child survived.
2001 – Discovery of Uranus’ moon Ferdinand. As far as we know, this 6 km wide moon, named after the King of Naples in Shakespeare’s The Tempest, is the most distant from the planet.

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July 01 – Discovery of Asteroid 6 Hebe (1847)

First spotted by amateur Polish astronomer Karl Ludwig Henke from his observatory at Driesen on July 1st 1847, asteroid 6 Hebe is a large main belt asteroid, and at magnitudes of up to +8.3 at opposition only four others are brighter. Hencke only found two asteroids, the other being 5 Astraea. But Hebe turned out to be quite an important discovery because it seems we might have quite a lot of it here on Earth. It is possible that as much as 40% of all Earth-striking meteorites (the H chondrite meteorites) originate there, although a 2017 paper by Marsett et al casts doubt on this theory. Their studies of Hebe suggest that it doesn’t appear to have lost enough of itself to be responsible for such a large volume of H-chondrites.

Hebe, by Antonio Canova (image credit: Mak Thorpe, 1999).
Hebe, by Antonio Canova (image credit: Mak Thorpe, 1999).

Hebe, Greek goddess of youth, was a daughter of Zeus and Hera. Her Roman equivalent, Juventas, gives us the word ‘juvenile’, as well as a fine football team, so called because they were founded by a group of young students.

1884 – Discovery of asteroid 238 Hypatia by Russian astronomer Viktor Knorre, son of Karl Knorre, and grandson of Ernst Knorre, both of whom were also pretty famous astronomers in their day. Hypatia is a C-type main belt asteroid of about 145 km wide, named after a Greek philosopher of the neoplatonist school, murdered by Christians in 415 AD.

2013 – Discovery of the as-yet unnamed moon of Neptune, S2004 N1.

May 01 – Discovery of Neptune’s moon Nereid (1939)

Neptune’s third largest moon, Nereid, was discovered on May 1st, 1939, by Gerard P Kuiper, using the 83-inch Otto Struve Telescope at Mcdonald Observatory, Texas. It is about 170 km in diameter, and has a day lasting just 11.5 hours, but a year almost identical to ours, at 360 days.

Not Voyager 2's greatest photograph, but the best we have of Nereid (image: NASA).
Not Voyager 2’s greatest photograph, but the best we have of Nereid (image: NASA).

Nereid has a prograde rotation, and a very eccentric orbit, which takes it from 853,000 miles at periapsis to 5,999,000 miles at apoapsis. This has led astronomers to believe it is either a captive asteroid (or Kuiper Belt Object) or has had a previously more normal orbit changed by the capture of Triton.

The Nereids after whom this moon is named were the fifty daughters of Nereus and Doris. They were sea nymphs who attended Neptune (he married one of them, Amphitrite, who bore his son Triton.