an observed binary star G type (like the sun) from a hypothetical planet with about 0.5 degrees of angular diameter in the sky would suggest that both would be around one astronomical unit away, but you could have such a close red dwarf and a distant blue giant with the same apparent diameter, but no doubt they would look substantially different, both in color and brightness .
So if the two suns are the same size and are about the same distance, then it is likely that you are standing on a planet circumbinario (like the fictional planet Tatooine Star Wars universe) that surrounds both stars in an orbit.
circumbinaria To allow stable orbit - you must meet two conditions are either a) that the planet must be very distant from the binary stars (which essentially act as a single center of mass) or b) that the two stars are very close together - so act essentially as a single center of mass. It is unlikely that a planet could maintain a stable orbit around a binary system where it is exposed to pulses of gravitational force, created when two stars approach the planet, on a regular basis.
Anyway, if you can stand on a planet and see a set of binary suns - and a way of life based on the water, then, your planet is within the habitable zone system stars, the area where water can exist in liquid form. Given this - and its apparent size and proximity to each other, most likely, you orbiting two stars who are really close together.
hypothetical set of 2 stars with an apparent diameter equal to the sun on a planet circumbinaria with an orbit around them. Crédito.Nasa.
to get a planet in the habitable zone around a binary choice is probably limited to circumbinarios planets around two nearby stars or circumstellar planets around a star in a binary system widely scattered. Credit: NASA / JPL.
But, bearing in mind, that if one accepts that there are two G-type stars in the sky, then it is unlikely that the planet is exactly one astronomical unit from them - and that the presence of two stars in the sky should be equivalent approximately double the flow obtain stellar one. And it's not a simple matter of doubling the distance to reduce by half the stellar flux. Doubling the distance will reduce by half the apparent diameter of stars in the sky, but an inverse square relationship applies to its brightness and solar flux, as twice as far only get a quarter of its flow star. Therefore, something like the square root of two, ie about 1.4 astronomical units away from the stars, could be the right distance.
However, this means that the stars now need a larger diameter than the sun to create the same size were apparent in the sky - which means they should have more mass, what would a more intense spectral class. For example, Sirius has 1.7 times the diameter of the Sun, roughly double its mass - and thus about 25 times its absolute luminosity . So even at 2 astronomical units away, Sirius would be nearly five times brighter and deliver five times the stellar flux of what makes the sun to the earth (or ten times, if there are two such stars in the sky) .
So, in summary ...
is a problem to reach a stage where they could be two stars in the sky with the same apparent size, color and brightness (the sun) and keep the planet in the habitable zone - unless the planet is in orbit around circumbinaria two star equivalent. There is no reason to doubt that a planet could maintain a stable circumbinaria orbit around two stars equivalent to G type could be similar to the Sun or any other type. However, it is a struggle to arrive at a plausible scenario where these stars could maintain its angular diameter in the sky that appear to be, while keeping the planets in the habitable zone of the system.
words, if you're in a desert world, but with two stars of spectral class more intense than the G is likely to be expelled from the atmosphere of the planet - and up to two G-type stars, such a scenario would give Venus (which receives about twice the solar flux to Earth, being 28% closer to the Sun .) Could be smaller stars of the class K or M, but then they should be more red than they appear to be - and their planet would be closer to them, to the point where it is unlikely that the planet could maintain an orbit stable.
more information HERE
source of information:
http://www.universetoday.com/83238/astronomy-without-a-telescope-plausibility-check/
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