Astronomer’s Valentine

True lovers love to bring each other the stars from the sky. So, here is my suggestion for tomorrow as a constellation expert:

Did you recognise it? Although I nicknamed the constellation on the occasion of Valentine’s Day, the constellation itself really exists – and has been documented since Greek antiquity. There is no evidence of it in Babylonian times, but Ptolemy (137 CE), Hipparchus (~130 BCE), Eratosthenes (220 BCE) and Aratus (4th century BCE) describe it, and no earlier Greek uranographies are known to date. Our ancestors referred to the constellation as ‘The River’, now called Eridanus (NoirLab, IAU-WGSN website), and it is easily recognisable: directly next to prominent Orion (of course, it works best in the northern hemisphere).

Transformation of Eridanus over time

According to the official nomenclature of the IAU, which has been in use since 1930, the constellation extends much further south – something the ancient Greeks and Babylonians could not see because it was below their horizon. Here is a comparison of the Ptolemaic and modern constellations:

The modern constellation (Delporte 1930) reaches much further south than the ancient one. This change was made by Dutch cartographers (Plancius 1596, de Houtman 1603) in Early Modern time and propagated ever since. As a historian of celestial cartography, I suspect a mistake in the ancient Almagest as the source of this change: the Almagest claims (in words) the southernmost star of The River to be a first magnitude star and the brightest one of the constellation. However, the star at the coordinates of the southernmost mentioned (theta Eridani) in the Almagest is not the brightest. When European (Dutch) sailors travelled far enough south to see a first magnitude star, they extended the winding cosntellation line (as the also enlarged Argo, The Ship, equipping it with sails). They even extended The River to the southern pole (perhaps a navigation aid?), but in consistency with the wording in the Almagest, later cartographers only maintained the part up to the first magnitude star. Now, the IAU recognises two stars with the Arabic name for “the last one of the river:” the original one and the bright one.

Today, the ancient river is called ‘Eridanus’, but in ancient times this was not so certain: 2000 years ago, the official name of the constellation was “River”, and Pseudo-Eratosthenes wrote that “it is called Eridanus. Others say that it is most certainly the Nile, because it is the only river that has its source in the south.” Elsewhere, even in ancient times, it was suggested that it could also be the River Po in Italy. So we are on the safe side when we say that it is simply a river.

Romantic Star Lore (for Planetaria)

Astronomers in particular are commonly assumed to be especially romantic. This has even been immortalised in a Greek star legend which is unable to explain conclusively why the constellation Pisces (IAU WGSN, NoirLab) depicts two fish tied together with a ribbon that also has a knot in it. (I do have a historical explanation, though, but it is completely unromantic and doesn’t fit here.) Greek mythology offers various interpretations for this.

Legend 1

One version is that the fish in Pisces are transformed gods or demigods (e.g. Aphrodite and her son Eros, or others in variants of the legend). They are on the run and therefore have to go their separate ways at some point (around the autumn quadrangle) — but they remain eternally connected by the ribbon of love:

Anyone who wants to flirt like that has to assume that their partner has a great deal of knowledge. Ian Ridpath’s Star Tales have more variants of the story behind Pisces and not all of them are romantic. However, the background of this love story in Pisces is that the “Heavenly Lady” in our constellation Andromeda (ASE, IAU WGSN, NoirLab) originally was the Babylonian goddess of love (and war: as Pat Benetar says “love is a battlefield“), whose Syriac variant Derketo is typically depicted with (one or many) fish as her attribute. 

Hence, Andromeda actually is a goddess of love.  

Legend 2

Another romantic star tale is connected to the constellation Coma Berenices (Ian Ridpath Star Tales). The constellation Coma (IAU WGSN Website, NoirLab) is first reported by Eratosthenes and invented by the Egyptian court astronomer in his time (according to the Graeco-Egyptian legend that he reports) to honour the Queen of Egypt, Berenice Euergetis (the Beneficent). She had sacrificed her beautiful curls in the temple while praying for her husband’s safe return from a war. When the magnificent bunch of hair had disappeared a few days later upon the king’s return, the astronomer Kolon claimed that the gods had placed it in the sky as a symbol of marital love and fidelity.

Modern Astrophotographers

Without any legend, history or fairy tale, modern (amateur) astronomers like to come up with deep sky photography objects that are equally explicite. The Astronomy Picture of the Day (APOD) of Valentine’s Day 2022 again showed the Heart Nebula in the Milky Way in constellation Cassiopeia. 

In many years (e.g. 2014, see below), the APOD even displays The Heart and The Soul nebulae together for Valentine’s Day – and The Soul can alternatively be interpretated as a human baby which is frequently the result of the love between a man and a woman. 

Unfortunately, this heart (and baby) in the sky can only be seen with technical aids. It is large, but too faint for the human eye. My ‘heart for astronomers’ (Eridanus) above can be easily seen with the naked eye – and it is even very easy to find, as it is right next to the famous constellation Orion: right next to the foot star ‘Rigel’.

Orion bottom left,
Cassiopeia top centre:

Good luck, boys and gentlemen, 

Go and conquer your lady’s heart!

---

note: in many cases, flowers will also do 😉