imagine there are 2 suns

we live in earth, which around the sun. the earth orbits around the sun like a perfect circle. because of this circular orbit, the earth's temperature changes little bit. average is 13 degrees and from -89 degrees, to 58 degrees. see the following graph:

Mean January air temperature for the Earth's surface, 1959-1997. 


This is the temperature distribution of earth. most temperature is around 0 to 40 degrees. compare to other planet, like mercury, its surface temperature is as high as 200 degrees and due to this high temperature, small gravity and strong solar wind, all air of it are gone, evaporated! and compare to mars, the average temperature is -47 degrees.

thus, if the earth is not move like a circle, it will get very hot when close to sun, but very close when far away. this big temperature different makes life hard to exist. this is because no know life form on earth can cope with such big temperature different. and also, the protein, and cell membrane cannot stand for this temperature change. but never the less, there may be some life form can stand with this change but we just not discover it yet.

In additional to temperature, the weather also goes crazy. the weather on earth is mainly coz by the temperature different on earth. the hot air goes up and cold air goes down and it makes the rain and weather! so , fluctuation on temperature will coz large change in weather.

OK. what is it about "if there are 2 suns" ? if there are 2 suns, then the orbit of the earth will but so complicated and a simple circular orbit does not exist. some orbits may just therefore, if there are any planet with 2 suns, their orbit is always irregular. and an irregular orbit will result large temperature different.

moreover, our earth motion creates day and night, for so many year, it just changes a bit. and it help creature build a biological clock. but when there are 2 suns, the day and night will goes crazy. one tricky thing may happen is the cycle of the 2 suns are in prime number. say, 1 sun goes 7 hours for completing a cycle while another sun is goes 13 hours. thus, a complete cycle is 7x13 = 91 hours ( the LCM). with in this 91 hours, the day and night time is like this:


you see there are very short day and night some time, while very long sometime. this again, it very difficult for creature to adopt or to develop a energy spending and storing style, which it what the biological clock for. the clock tell it, it is time to spend energy, and it is time for eat, store some energy. Never the less, there many be some creature in space can stand for this crazy living style.

the day time and night time, positive is day, negative is night. the x-axis is hour.

for comparing, this the the day and night of earth.

(* graph by wolframalpha.com *)

there fore, when scientists are looking for some planet that may have life form. they always looking for a single sun system. because it can have circular orbit. and stable orbit.


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there may be a stable orbit for 2 sun system. the 2 suns are orbiting each other close by and the planet just far away of them. when looking at far away, the 2 closed-sun like 1 single sun. the other way is 1 sun is so big and the other is like a planet circulating around. it is similar for a bigger size solar system, while the Jupiter becomes a sun.

but in the case the 2 suns are similar size, and the planet are not far away, there are not stable orbit on it.