## Distance of planets from stars and revolution

 There are too many uncontrolled variables there. You speculate a planet with a 7300day orbit, about a star which is hot enough that this distance is still inside the life zone of the star. Presumably you also want the entire orbit inside the life zone - which limits how eccentric the orbit can be. you need to orbit farther out to get the period longer but then you need a hotter star and they tend to be more massive too so you have to go farther out still. If you are thinking in terms of sci-fi then you should try getting a copy of Steve Jackson Games: GURPS Space - it has a table of life-zones with stars and the formulae needed to compute the orbit period. You can check the orbit periods in the life-zones of each kind... give you a simple rule. Of course not all kinds of stars would have planets "in the wild".
Yes, actually my interest for the question is more sci-fi, perhaps i should specify it.

Yes, i figure it out! A 20 years period needs hotter star.

Is so impossible esteem the distance? Where can i find this table of line online?

Aside from this..

Could a reasonable fraction are outside the life zone but without affect life, or however how life and seasons would affected in these situation? Especially the fraction outside the life zone.

and let me..what if planet spin much faster then earth? Could this affect (surely of corse) the whole airstreams's development mainly about strength?

Sorry if it's much sci-fi you not have to reply.

Mentor
 Quote by Simon Bridge @qraal: doesn't that imply that the same Mp/M* ration gives the same orbital period regardless of the radius (semi-major axis) of the orbit?
No. What qral meant to say (or should have said) was the orbital period is inversely proportional to √(1+Mp/M*) for a given semi major axis length. The generic formula in Newtonian mechanics for the Keplerian orbital period of some planet p about some star s is
$$\left(\frac{T}{2\pi}\right)^2 = \frac{a^3}{G(M_s+M_p)}$$
Note that this implies that Kepler's laws are only approximately correct. Kepler's laws as stated by Kepler are good to about 3 decimal places. Newtonian mechanics ups the accuracy considerably, and general relativity improves things even more.

 Mentor The luminosity is rising quicker than the mass, therefore hotter stars may allow an orbital period of 20 years in the habitable zone. With some numbers from wikipedia: For main-sequence stars, the luminosity L of a star with mass m is approximately $\frac{L}{L_{\odot}} = \left(\frac{M}{M_{\odot}}\right)^a$ with a~3.5, where the denominators are the sun's values. The radius r of the habitable zone scales with $r \propto \sqrt{L}$ and therefore $r \propto M^{a/2}$ and $T \propto M^{3/2a-1} \approx M^4$, neglecting the mass of the planet. To get an orbital period of 20 years with earth-like conditions, it is enough to have a star with ~2.1 times the stellar mass. However, the lifetime of the star is significantly smaller (by a factor of ~5-6), and life would not have 5 billion years to evolve there.

I'll have hard time devicing my answers...

 Could a reasonable fraction are outside the life zone but without affect life, or however how life and seasons would affected in these situation? Especially the fraction outside the life zone.
Assume that planet can develop life. Have any edeas about?

More mass the planet have, greater is its gravity. But could be planets bigger then the earth but with minor or equal mass?

 Thread Tools

 Similar Threads for: Distance of planets from stars and revolution Thread Forum Replies Quantum Physics 8 Special & General Relativity 1 Introductory Physics Homework 2 General Astronomy 10 General Astronomy 4