Talk:40 Eridani

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Unless the browser fills a display, that wide infobox is going to crowd out the text from the lead section. The resulting appearance is less than aesthetically pleasing. Can the width be reduced in some manner? Thank you. — RJH (talk) 21:46, 15 June 2007 (UTC)

Star Trek connection[edit]

The first hint that Vulcan orbited 40 Eridani was in the James Blish novelization of the 1967 episode "Amok Time", but it would be 37 years before it was "canonized" on-screen. In the meantime, no clear indication was given of Vulcan's location - it was certainly in Earth's "stellar neighbourhood" and easily reached in a few days or hours depending on the warp speed limit of a ship. Spock indicated that his world's sun was extremely bright, which muddies the issue since a K-type star would not be as bright as a G-type star, and a star such as Fomalhaut or Sirius would be indicated.

The issue was finally settled in 2004 when Trip Tucker mentioned about traveling 16 light years to get to Vulcan, attaching to the assorted other references in Star Trek lore that consistently mention Eridanus as the location. 40 Eridani is the right distance, and harkens back to James Blish's novel. James Blish, in turn, used earlier drafts of scripts for his novelizations, so it is possible that in an earlier draft, Kirk does indeed tell USAF Capt. Christopher that Vulcan orbits 40 Eridani, but for whatever reason, that dialogue was removed before the final shooting script. GBC (talk) 04:41, 21 February 2008 (UTC)

The Star Trek banter belong under "In Popular Culture". Make it so. (talk) 00:14, 30 August 2013 (UTC)

habitable zone[edit]

According to the third kepler law, i found that the year of the hypothetical planet is 190 days and not 203 as said.--Efemero (talk) 12:46, 26 March 2009 (UTC)

I read the source (cumming et al 1999) an find no reference to the 203 days. I made all the calculs and find that 203 days correspond to a 0,63 UA orbit. the definition of habitable zone give a result of 0,63 UA for 40 Eridani A, thus the source (a website without math) is wrong. 0,61UA -> 190 days and 0,63 UA -> 203 days but not 0,61 -> 203...—Preceding unsigned comment added by Efemero (talkcontribs) 20:12, 18 May 2009

The 0.613 AU only works for a 203-day year if you take Roger Wilcox's Internet Stellar Database's estimate for the mass of 40 Eridani as 0.75 the mass of our sun, which must be outdated. But, what confuses me is that Roger Wilcox only described 0.613 AU as the 'Visual' Comfort Zone equivalent. 40 Eridani gives off a greater percentage of its energy output in the infrared, than our sun does. So, its 'bolometric', its real habitable zone, is probably even further out than 0.63 AU, nearer 0.70 AU or even beyond that. I do not know the physics formula you would need to calculate how much further out the real habitable zone would lie. I think 0.61 AU sounded like a very rough and ready estimate, from the start, for the habitable zone around 40 Eridani. —Preceding unsigned comment added by (talk) 09:08, 14 April 2010 (UTC)
It depends which measurements you choose to use (for example from this article) and how accurately, to how many decimal points, your calculations were made. Using Microsoft Excel 2007 for my calculations I get 199.624 days for 0.63 AU and 0.64 AU for the 203 days. But, if I were to calculate the luminosity, from the radius and effective temperature, given in this article (Temperature effective 5300 Kelvin and Radius 0.81), then the luminosity is 0.4640, 46.40 percent, that of the our Sun, and the habitable zone (the distance from 40 Eridani A where the temperature would equal that averaged on Earth simplistically using just the bolometric luminosity to calculate it), is at 0.681 AU instead of 0.63 AU. The orbit would then take 223.45 days. However, if I use just the Apparent Magnitude to calculate the bolometric luminosity habitable zone in the same way, then my calculation agrees with yours, in at least with the distance from the star, at 0.6303 AU. 0.613 AU fits perfectly well, if you take the Mass for 40 Eridani A as 0.75 that of the sun, the mass Roger Wilcox gives (he does use math) for 40 Eridani A, instead of the 0.84 this Wikipedia article just happens to have sourced.— Preceding unsigned comment added by (talkcontribs)
In the past I've found some errors at the SolStation site being used here as a source, so I tend to view it as somewhat dubious (although it can be a good starting point). My preference would be to use a more authoritative reference. Regards, RJH (talk) 16:36, 6 September 2011 (UTC)

Assertion that flares would be lethal to life[edit]

I've tagged the assertion that the flares on 40 Eridani C would be lethal to life as dubious. There are studies out there that suggest that flares would not preclude biospheres on orbiting planets and may in fact be necessary to drive biomolecule production in the habitable zones of red dwarf stars. E.g. this paper which appeared in Icarus: [1] Icalanise (talk) 10:02, 13 May 2010 (UTC)

Apparent Width of 40 Eridani A[edit]

I changed the width of how 40 Eridani A would appear from a planet in its habitable zone, at 0.68 Au, relative to the size of how the Sun appears from Earth's surface. From the dubious 30 percent, given in the article, to what I calculated, 20 percent. I calculated it as follows, using some simple algebra. (I am sure there must the same formula and better described, somewhere else in wikipedia, but I can't find it):- At 0.68 AU from 40 Eridani A, a hypothetical planet would be receiving the same wattage or power from the star, upon its surface, as Earth does from the sun. The bolometric luminosity received at the surface would be the same for both planets. The cooler a star the larger the star appears in the sky for it to be equally luminous, to give the same power. So, the size of the star seen from a planet at the habitable zone is solely determined by its temperature. For example, if our Sun was much smaller, like a white dwarf, the habitable zone would be closer to the white dwarf but the white dwarf would still appear the same size, as we presently see the sun from Earth, so long as the temperature of the white dwarf was exactly the same as our sun's. In a similar manner, imagine 40 Eridani A was much larger, than it is, and the habitable zone was out at 1.00 AU from the star. 40 Eridani A would have to be to provide the planet with the same bolometric luminosity, as the sun does for Earth, for the habitable zone to be at 1.0 AU. But this larger 40 Eridani A, would appear the same size from a planet in its habitable zone as 40 Eridani A does presently from 0.68 AU, if it were still the same temperature, 5300 Kelvin. So, using that example, L=4π(Rsun^2)σ(Teffsun^4)=4π(R40EridaniA^2)σ(Teff40EridaniA^4)=1. Divide all sides of the equation by known constants, 4π and σ also by the bolometric luminosity which is 1 and the radius squared of the sun. Gives, R40EridaniA^2/Rsun^2=Teffsun^4/Teff40EridaniA^4. So, the relative radius size (R40EridaniA^2/Rsun^2) of 40 Eridani A as seen from a hypothetical planet in the habitable zone, compared to how the sun appears from Earth is, RelativeRadius=squareroot(Teffsun^4/Teff40EridaniA^4). And of course, the relative radius size difference is the same as the relative diameter size difference. So, RelativeDiameter=squareroot(Teffsun^4/Teff40EridaniA^4)=1.1885, or 19 percent wider. — Preceding unsigned comment added by (talk) 20:51, 17 September 2011 (UTC)