I just recently watched the JJ Abrams Star Trek film. It depicts the destruction of Vulcan by means of Red Matter. Does anyone know some basic facts about Vulcan?

  • What was Vulcan's astronomical coordinates?
  • What sun did it orbit?
  • Did it have a moon?

The real-world planetary inspiration is not canonically established, but in 1991 Gene Roddenberry and some astrophysicists endorsed 40 Eridani A, over Epsilon Eridani, as the star Vulcan orbits.

Star Trek 2 (1968) by James Blish and Star Trek Maps (1980) by Jeff Maynard named 40 Eridani A as Vulcan's star while Star Trek Spaceflight Chronology (1980) by Stan and Fred Goldstein cited Epsilon Eridani as the home system.

Roddenberry, Sallie Baliunas, Robert Donahue, and George Nassiopoulos put the two stars under the "microscope" to determine which star could theoretically fit the bill to be Vulcan's home:

We prefer the identification of 40 Eridani as Vulcan's sun because of what we have learned about both stars at Mount Wilson ... observations suggest that 40 Eridani is 4 billion years old, about the same age as the Sun. In contrast, Epsilon Eridani is barely 1 billion years old. ... based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria. On the other hand, an intelligent civilization could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun.

That puts Vulcan around 16.5 light years from Earth.

As far as moons, Vulcan has none, but may have a sister planet (based on episodes from Enterprise and The Original Series, and Star Trek: The Motion Picture)

The Star Trek novel Spock's World offers the explanation that the "moon" appearing in the Vulcan sky in "Yesteryear" and the original cut of Star Trek: The Motion Picture was actually the sister planet of Vulcan, called T'Khut. This theory is widespread in other non-canonical works like Star Trek Maps, Star Trek: Star Charts and The Worlds of the Federation. This was "corrected" in the DVD release of Star Trek The Motion Picture with the removal of these worlds.


It's generally considered to be part of the Epsilon Eridani system. And it didn't have a moon so much as it had a sister planet of close to the same size (astronomically speaking).

  • According to wiki it was author James Blish who said this first and later adopted by Roddenberry – Sinan Jun 6 '11 at 18:40
  • @Sinan You are correct, but as I re-read the wiki entry for Vulcan, I read that Epsilon Eridani and 40 Eridani A (the star that Roddenberry, Blish, and others state as Vulcan's star) are not the same thing. This answer is wrong. I've rolled it back to remove the link to Memory Alpha's 40 Eridani A entry. – Ryan Jun 6 '11 at 21:38

According to the Enterprise episodes "Home" and "Daedalus" Vulcan's star is about 16.0 to 17.0 light years from Earth.

In "Home" Tucker and T"Pol are on Vulcan when:

T'POL: Trip, I have to do this for many reasons. TUCKER: And how am I supposed to take this? T'POL: I'm sorry. TUCKER: You're sorry. You brought me sixteen light years just to watch you get married to someone you barely know.

In "Daedalus":

EMORY: Sub-quantum teleportation. You step on to a transporter on Earth, a few seconds later, you're on Vulcan. TUCKER: That's over sixteen light years.

Therefore the distance from Earth to Vulcan's star system must be between 16.0 and 17.0 light years.

epsilon Eridani is about 10.48 light years from Earth and not in that range.

The only star systems in that range that don't contain only red dwarfs, white dwarfs, brown dwarfs, and other unsuitable stars are: 40 Eridani or Omicron 2 Eridanai, 70 Ophiuchi, and Altair.

In "Operation Annihilate" Spock said:

SPOCK: An hereditary trait, Captain. The brightness of the Vulcan sun has caused the development of an inner eyelid, which acts as a shield against high-intensity light. Totally instinctive, Doctor. We tend to ignore it, as you ignore your own appendix.

Since Spock mentioned the brightness of "the Vulcan sun", we may assume that only one stars is close enough to have a visible disc and contribute much heat and light to Vulcan.

Altair is the only single star of the three best choices on the list, and it has the most intense light of any main sequence star on the list.

But in "Amok time" the Enterprise was being sent to Altair VI at the same time Spook needed to go to Vulcan. If Vulcan was in the same star system as Altair VI travelling even a hundred million miles between them would not take a starship long enough for a scheduling conflict. So Altair is out.

That leaves two multiple star systems to choose from. Since Spock mentioned "the Vulcan sun", Vulcan must orbit one star in that star system and the other one or two stars much be far enough away from Vulcan and its star that they appear as stars in the sky of Vulcan instead of as suns.

In 70 Ophiuchi the to stars orbit at distances from 11.4 to 34.8 AU.

The primary star is a yellow-orange main sequence dwarf BY Draconis variable[3] of spectral type K0, and the secondary star is an orange main sequence dwarf of spectral type K4.[2] The two stars orbit each other at an average distance of 23.2 AUs. But since the orbit is highly elliptical (at e=0.499), the separation between the two varies from 11.4 to 34.8 AUs, with one orbit taking 83.38 years to complete.[11]


40 Eridani A is a main-sequence dwarf of spectral type K1. 40 Eridani B and C, are a 9th magnitude white dwarf (spectral type DA4) and an 11th magnitude red dwarf flare star (spectral type M4.5e), respectively. Presumably, while B was a main-sequence star, it was the most massive member of the system, but ejected most of its mass before it became a white dwarf. B and C orbit each other approximately 400 AU from the primary star, A.[8] Their orbit has a semimajor axis of 35 AU (which is the approximate average distance between B and C) and is rather elliptical (eccentricity 0.410).[7]


Since B is a white dwarf that probably once lost a lot of mass in a spectacular way, neither it or its relatively close companion C is likely to have habitable planets.

But A, about 400 AUS from B and C is much more likely to have habitable planets.

An observer on a planet in the 40 Eridani A system would see the B/C pair as unusually bright (magnitudes -8 and -6) white and reddish-orange stars in the night sky. This is not bright enough to diminish the darkness at night, though they would be visible in daylight (assuming an Earth-normal atmosphere). (By comparison, Earth's full moon is magnitude −12.6, and Venus at its brightest is −4.7.)

Thus only 40 Eridani A would look like a sun in Vulcan's sky if Vulcan orbits 40 Eridani A in the habitable zone.

At the nearest distance between 70 Ophiuchi A & B, 11.4 AUs, or about 1.059984 billion miles, a degree of arc would be 9,250,000 miles.

The diameter of the sun is 864,575.9 miles. 70 Ophiuchi A should have a diameter of at least 0.88 of Earth's Sun and thus of at least 760,826.79 miles. Thus it would appear to be 0.0822515 of a degree from 70 Ophiuchi B at their closest.

Normal - Human - visual acuity is about 0.6 of an arc minute, or about 0.00999 degrees of arc. Thus at their closest 70 Ophiuchi A would appear about 8.22 times the minimum width necessary to b e seen as a sun and not as a star.

70 Ophiuchi B has about 0.220 times the luminosity of 70 Ophiuchi A and thus might have only 0.469 times the diameter of 70 Ophiuchi A, but should still be visible as an object and not a star at the closest distance between the two stars, being 3.828 times the minimum necessary width. But 70 Ophiuchi B is cooler than 70 Ophiuchi A and so has to have more than 0.220 times the surface area of 70 Ophiuchi A to emit 0.220 times the radiation as 70 Ophiuchi A.

So 40 eridandi A seems to be the most likely star for Vulcan to orbit around.

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