ERIDANUS: THE CONSTELLATION OF VULCAN

by Marco "Sabich" Vittorini

Eridanus (Eridanus, Eridani or simply Eri) is a wide constellation only partly visible in late autumn and winter. It extends for 1138 square degrees, starting in a point near the celestial equator close to Rigel (in the constellation of Orion), then proceeding to the south of Taurus and finally expanding southwards. Its biggest star is Achernar (Alpha Eridani, magnitude 0.6 - 142 light years from Earth, bigger than Sol and at least 200 times brighter) which is visible only from the Southern Hemisphere. Apart from this, Eridani does not contain any more stars brighter than the third magnitude, even if it has about 300 heavenly bodies, which are visible to the naked eye.

Eridanus' most interesting peculiarity is that it includes 40 Eridani A, the star of Vulcan's planetary system (see the "Star Trek Encyclopedia" by Mirek and Okuda). It is interesting to observe that this star was never mentioned in any episodes of the original series, nor in any of the subsequent films, and therefore it may be legitimate to wonder where this information has its source. Vulcan's collocation in the firmament was in fact made by Gene Roddenberry himself, in one of his works dated July 1991, on the occasion of Star Trek's saga twenty-fifth anniversary. As I said, there is no explicit reference in any films or episodes, but there are at least two names that often crop up in the immense Trek literature. "Star Trek 2" (J. Blish, Bantam 1968) and "Star Trek Maps" (J. Maynard and others, Bantam 1980) suggest 40 Eridani like a possible Vulcan sun. "Star Trek Spaceflight Chronology" (S. & F. Goldstein, Pocket 1980) proposes instead Epsilon Eridani, which, anyway, belongs to the same constellation. Between these two, Roddenberry preferred 40 Eridani, giving the reason for his decision as being the esteemed age of the stars. In fact, 40 Eridani is 4 billion years old, approximately the same age as Sol, while Epsilon Eridani is much younger, being "only" one billion years old (give or take a century). If we base our assumptions on Earth's history, life on a planet, which revolves round Epsilon Eridani, couldn't have had time to develop much more than the level of the bacteria. On the other hand, a logical and intelligent civilisation could have developed much more easily on a planet revolving round 40 Eridani. Roddenberry thus chose Vulcan's sun.

It is therefore important to talk a little about this star, which reveals some extraordinary surprises. In reality 40 Eridani, also known as Omicron-2 (it constitutes in fact, with Omicron-1, a large pair of stars in the Eridanus' wide constellation), is a unique triple star system, made up of three stars that will be called A, B and C components. The main is the A component, "only" 16 light years (4.9 parsecs) from Earth. It is an orange star with magnitude 4.48 and it has a double companion made by the B component, which is a white dwarf (only visible through little telescopes) with magnitude 9.7 and the C component, a red dwarf with magnitude 10.8. The exceptional thing about this system is that the B and C components, 2 light days (40 billion miles - an enormous distance!) from the A star, revolve around each other with a period of approximately 252 years (keeping between them an average distance of 4.1 billion miles, more than the distance between Sun and Pluto) and at the same time they revolve round the A component with a period of approximately 8000 years. All this would seems, with the right proportions of course, like Sol - Earth - Moon system.

With a little effort of the imagination you can try to imagine how Vulcan's sky might appear. Considering the relation between Sol and 40 Eridani A, Vulcan might revolve round its star on an average distance of approximately 52,360,000 miles, like a solar orbit displaced between Mercury and Venus. 40 Eridani A might therefore shine in Vulcan's sky much like Sol does in that of the Earth. At this distance, 40 Eridani A might appear to be an inflamed disk 62% wider than Sol's disk seen from Earth. The B and C components, on the contrary, are too far to look like disks: they might rather appear like two bright points, rather close to each other, 6 times brighter than Venus seen from Earth, also visible in broad daylight although the distance prevents them from contributing in a significant way to the planet's illumination and warmth. By night, their light might naturally be emphasised until 22 times that of Venus, or 1/47 of the full Moon's luminosity.

Sabich

Look for Eridanus in charts.

• Where is Vulcan - G.Roddenberry - 1991
• Astronomia - various authors - Italy, Fabbri 1991
• Il libro delle stelle - P.L.Brown -Italy, Mursia 1975
• Atlante di astronomia - J.Herrmann - Italy, Mondadori 1975
• Il cielo - G.Cecchini - Italy, UTET 1969