Vulcan years vs. Earth years

[NSTrekfan]

40 Eridani A is less massive and therefore less luminous than the sun. In order for a planet to have an Earthlike climate it must orbit 40 Eri A closer than the Earth orbits the sun. 0.56 au puts it somewhere between Mercury and Venus if it were in our solar system but in the 40 Eri A system it would get about the same amount of energy at that distance as Earth does at 1 au from Sol.


Moving it out to .855 au as you suggest means, due to the inverse square law, it would only receive 43% as much energy as Earth does now. Add the thinner atmosphere and you'd end up with something more like Mars. Hardly "Hot as Vulcan".

 

[Captain Robert April]

Would 40 Eridani B and C add anything to the mix?

 

[NSTrekfan]

Nope, too dim and too distant. From Sky & Telescope:

"Both B and C are bright enough to be easily visible in Vulcan's daytime sky, though (at their distance) they wouldn't really be contributing much to Vulcan in the way of light and heat. At night, they would shine with a combined magnitude of -7.8, some 22 times brighter than our brightest Venus--though still only about 1/47th of the brightness of our full Moon. Enough to cast a dim shadow, maybe, and annoy the hell out of Vulcan astronomers around the time that B and C are in opposition, but dim enough to let night remain night."

 

[Timo]

Hardly "Hot as Vulcan".

The more exact expression might deal with the Vulcan day. The nights are probably hellishly cold if the atmosphere really is that thin.

Really, the average temperature of the planet might be very low, and the desert days might still be as hot as any on Earth, in terms of radiated heat. It can get "scorching hot" up on the mountains of Earth, too - at low actual temperatures.

It's not as if any of the characters would ever have been shown sweating on Vulcan... Whereas Tuvok was sweating on a variety of desert worlds.

Timo Saloniemi

 

[NSTrekfan]

We've seen Vulcan at night in the closing scenes of TSFS. The crew arrives at sunset, spends the night at the ceremony and greets Spock as the sun comes up. They don't appear to be cold although it might be comfortable for them and the Vulcans find it chilly. In this shot, with the rising sun, we see the mountains are all bare rock, no trees as would be expected in a more temperate climate. Also, none of the mountains have a snow cap. On Earth, Kilimanjaro is located just 3 degrees from the equator and it's snow capped (although, not for long it seems).

I'd say there's evidence that the nights don't get substancially colder than the days.

 

[Captain Robert April]

Well, sorry, Gene, but 40 Eridani just failed as Vulcan's sun...

 

[NSTrekfan]

Not so fast. There's still possibilities. Are you using the original, DE or both versions of TMP? The companion planet, T'Khut for lack of a better name, may just be a help.

There's a study of co-orbital planets where they can actually exchange not only orbits, like the co-orbitals of Saturn but also their orbital eccentricty and yet remain stable. The science is a bit over my head but I'm slogging through. Essentiall, you'd have Vulcan have two mild season, each lastint 1/2 an orbit, then it would swap with T'Khut and have a very hot and a milder season before returning to it's previous orbit. 4 seasons would actually cover two orbits of the star but they would each be in differnt orbits. Vulcans may define "year" as returning to the starting point of the original orbit.

Check out the image in part 2 here:
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2010.17453.x/full

 

[Captain Robert April]

This is getting needlessly complicated.

 

[Ronald Held]

Vulcan has a thinnner atmosphere than Earth, so the greenhouse effect must be less. I would think that the average temperature is higher, which means closer than assume the global mean is 288 K.
T'Khut could in similar orbit or in the same orbit as Vulcan corotating around the CM. Not enough evidence to say which.

 

[Captain Robert April]

I think it's just a lot easier to figure that GR picked the wrong star for Vulcan (or, in the Star Trek unvierse, 40 Eridani is larger and a lot hotter than the real one, not unlike how Star Trek antimatter is a lot more volatile than the real thing).

 

[NSTrekfan]

Or there could be a way to get the various data points to work together.

Failing that, I'd tend to use the Sky & Telescope article over the TMP novelization because he got information from actual astronomers as opposed to simply making up some numbers that aren't based on anything.

 

[Captain Robert April]

^ And with 40 Eridani, it's gonna be a pretty tough row to hoe to get a hot, arid planet with a year that comes even close to 300 days.

 

[Ronald Held]

True.

 

[NSTrekfan]

If you want to keep the 300 days in a year then you'll need a star as massive or slightly smaller than Sol.

You can try http://stellar-database.com/

 

[jimcat]

Dear Captain Robert April,
I'm assuming these "notes" are from the "Star Trek" production office, and might be D.C. Fontana's own background notes. They're fascinating, and if it's a cunning ploy to get people interested in the release of the updated "Concordance", in my case IT'S WORKING!

Getting back to Vulcan's star, I think that the 0.91 (edit: 0.75! Sorry!) Earth-year length must have been subsequently dropped. The notes you quote specify four seasons in the year, and according to Gene Roddenberry's novel of "Star Trek: The Motion Picture", nine Vulcan seasons is 2.8 years, Earth time (see page 21). That has to mean a Vulcan year of around 1.25 Earth years, unless all the seasons are wildly different lengths. All is not lost, though, since if there are only two Vulcan seasons in a year (a hot season and a REALLY hot season?) then the Vulcans may count in groups of four seasons, units that are technically two years by strict definition. To avoid this explanation getting any more convoluted: Vulcans count in units of 1.25 Earth years, but the planet takes 0.63 Earth years to go once round its sun. Which puts 40 Eridani A back in the frame.

I've been playing with http://universesandbox.com/ to look at the options, and I'm beginning to see the outlines of a solution that works for me. There's no guarantee it will work for anyone else, though...

Timon

 

[Captain Robert April]

I think I'd rather go with the "40 Eridani in Star Trek is not the same as the real 40 Eridani" option.

 

[Ronald Held]

In ST:ENT they stated Vulcan was 16 light years from Earth, which is the distance from Earth to the 40 Eridani system.

 

[Captain Robert April]

There are nine star systems that are around sixteen light years from Earth, so 40 Eridani isn't the only option.

 

[Ronald Held]

How many of them are not M class, and are the same absolute magnitude or greater that 40 Eridani A?

 

[NSTrekfan]

Stars within 20 light-years (F, G & K only)

Sol: 0 light-years, class G2 V
Alpha and Proxima Centauri: 4.3948 light-years, class G2 V
Epsilon Eridani: 10.4968 light-years, class K2 V
Procyon: 11.406 light-years, class F5 IV-V
61 Cygni: 11.4269 light-years, class K5 V
Epsilon Indi: 11.8265 light-years, class K5e V
Tau Ceti: 11.8971 light-years, class G8p V
Omicron(2) Eridani: 16.454 light-years, class K1e V (40 Eridani)
70 Ophiuchi: 16.5881 light-years, class K0e V
Sigma Draconis: 18.8077 light-years, class K0 V
Gliese 570: 19.2642 light-years, class K5e V
Eta Cassiopeiae: 19.4149 light-years, class G3 V
36 Ophiuchi: 19.4649 light-years, class K1e V
82 Eridani: 19.7655 light-years, class G5 V
Delta Pavonis: 19.9186 light-years, class G8 V