enter image description hereI've been thinking of using a binary model (a planet that rotates around two suns) for a possible story.

The specific model is a S-type planetary system, where the planet orbits the the primary star A (0.8 M☉), while the secondary B (0.6 M☉) orbits the primary at a distance of 385 AU. the planet orbits around primary A at a distance of 0.85 AU.

The question is: what would the day and night look like in a circumbinary system of this type, and how could its configuration significantly affect the climate and seasons of this planet? enter image description here

  • 3
    $\begingroup$ At 385 AU the other binary star will look like a bright star in the night sky. It would be 40 times further than Pluto is from the Sun. $\endgroup$ – Samuel Mar 23 '18 at 2:35
  • $\begingroup$ This isn't circumbinary, this is [the other kind]. Source $\endgroup$ – SIGSTACKFAULT Mar 23 '18 at 3:08
  • $\begingroup$ @RonJohn It's an S-type. That means the planet orbits around one star that is itself in orbit around a barycenter with another star. $\endgroup$ – Samuel Mar 23 '18 at 3:10
  • $\begingroup$ Can you draw us a diagram? $\endgroup$ – SIGSTACKFAULT Mar 23 '18 at 3:15
  • 1
    $\begingroup$ @RonJohn, I looked into this a while ago. I can't be sure without doing the math, but a ballpark estimate is that the orbit is stable -- it's close enough to the primary and the secondary is far enough away. $\endgroup$ – Mark Mar 23 '18 at 5:33

If the secondary B (0.6 M☉) is 60% mass of Sun, we can assume it is a large red dwarf with luminosity about 7.2% of Sun's luminosity. Its absolute magnitude will be about 7.68. The distance is 385 AU, which gives us apparent magnitude of about -11. for comparison, full Moon's magnitude is -12.90, top brightness Venus' magnitude is −4.89 and Sirius (the brightest star) is −1.47.

The nighttime effect on the planet would be like from another Moon, which appears seasonally and does not have phases.

Gravitational pull of the star B at this distance will be extremely weak and detectable only with scientific instruments.

  • $\begingroup$ Thank you! Your answer has been very useful! By the way, the primary star due to the proximity would look bigger or a size similar to the sun? $\endgroup$ – JAMS Mar 24 '18 at 21:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.