How Bright are Manticore A & B?

ThinksMarkedly wrote: SNIP
That's about 33x more than the full moon on Earth, which in turn is enough to cast shadows.

Another tidbit: on Earth, the minimum brightness for something to be seen during the day is about -4. While the exact value for Manticore, Sphinx, and Gryphon depend on their atmospheres, we're talking about 12 magnitudes of difference. So either star is visible in any of the planets any time it has risen, even during daytime.

Robert_A_Woodward wrote:Absolute magnitude is the brightness at 10 parsecs (32.6 light years). Thus, the Sun with its absolute magnitude of 4.83 would be 100 times brighter (which by the way is 5 magnitudes) at 1 parsec (i.e., -.07 apparent). At .326 light years (3.0843X10^14 meters), it would have an apparent magnitude of -5.07. According to the data in _House of Steel_, the distances between Manticore-A and Manticore-B ranges from 650 to 827 light minutes. Let's use the 827 number and assume the distance is the same for the planet Manticore. That is about 1/12440 of the .326 light years. That means a magnitude increase of just over 10. The number I calculate for Manticore B (assuming it is as bright as the Sun), when viewed the Landing sky, is -15.57.

So it is v bright indeed. Again I had never thought of the daytime 'visibility' aspect.

I take Relax's point too. [Photometry was never a favourite subject!]
you have to consider both source area and source brightness when thinking about the amount of light falling on a surface - such as the earth.
We can see quite well by moonlight, because it covers a 'large' portion of the sky - even though it is actually not very bright.
These stars would be very bright, but because they would still be point like, the overall effect might not be so much.
Having said that I was quite surprised a few years ago to see a 'Venus' path on the sea, in the same way you can see a 'Moon' path, though much fainter. So, on the Maniticore planets you would see very bright equivalents indeed! Honor could well have used that in her sailing days!

Lots of hand waving going on here

isaac_newton wrote:Having said that I was quite surprised a few years ago to see a 'Venus' path on the sea, in the same way you can see a 'Moon' path, though much fainter. So, on the Maniticore planets you would see very bright equivalents indeed! Honor could well have used that in her sailing days!

Lots of hand waving going on here

For illumination, you mean? Not for navigation, I hope. It's better than navigating by Jupiter or Saturn on Earth, due to brightness and the moving very slowly relative to background stars, but it still moves.

ThinksMarkedly wrote:

isaac_newton wrote:Having said that I was quite surprised a few years ago to see a 'Venus' path on the sea, in the same way you can see a 'Moon' path, though much fainter. So, on the Maniticore planets you would see very bright equivalents indeed! Honor could well have used that in her sailing days!

Lots of hand waving going on here

For illumination, you mean? Not for navigation, I hope. It's better than navigating by Jupiter or Saturn on Earth, due to brightness and the moving very slowly relative to background stars, but it still moves.

haha - you're right of course. I should have put that better.

'been used to that' instead of 'used that'

I was thinking about it as a visual effect rather than something useful!

PS handwaving was by me - not others!!

https://futurism.com/how-does-the-sun-a ... er-planets

Neptune's around 250 light minutes out from Sol. Manticore A & B don't get closer than 650LM.

Robert_A_Woodward wrote:Absolute magnitude is the brightness at 10 parsecs (32.6 light years). Thus, the Sun with its absolute magnitude of 4.83 would be 100 times brighter (which by the way is 5 magnitudes) at 1 parsec (i.e., -.07 apparent). At .326 light years (3.0843X10^14 meters), it would have an apparent magnitude of -5.07. According to the data in _House of Steel_, the distances between Manticore-A and Manticore-B ranges from 650 to 827 light minutes. Let's use the 827 number and assume the distance is the same for the planet Manticore. That is about 1/12440 of the .326 light years. That means a magnitude increase of just over 10. The number I calculate for Manticore B (assuming it is as bright as the Sun), when viewed the Landing sky, is -15.57.

I made 3 mistakes in the above. One was minor, the other two were large, but offset each other. Let's try again.

We are assuming that Manticore-B is as bright as the Sun, thus having an absolute magnitude of 4.83 (which is at a distance of 10 parsecs) will give an apparent magnitude of -5.17 at .1 of a parsec (1/100th of the distance, 10 thousand times brighter, one magnitude is the 5th root of 100). Since 1 parsec is 3.26 light years, .1 parsec is .326 light years which is .326*60*24*364.24 light minutes (171,460). Using 827 light minutes, that results in a distance ratio of 207.3 which is squared to 42980 which is how much brighter it is compared to be .1 parsec away. Take the natural log of that, divided it by 1/5th of the natural log of 100 and the result is that the star is 11.58 magnitudes brighter, i.e., -16.75 when seen from the porch of Honor's modest vacation cottage on Jason Bay.

As a double check, 827 light minutes is close to 100 times the distance from the Sun to Earth. This results in a 10 magnitude decrease in the Sun's apparent brightness from -26.74 to -16.74.

That suggests that when the other star is visible you’ll have something like 10 lux everywhere, which is twilight level brightness, vic 40 times as bright as a full moon.

munroburton wrote:https://futurism.com/how-does-the-sun-appear-on-other-planets

Neptune's around 250 light minutes out from Sol. Manticore A & B don't get closer than 650LM.

Yup - I was just using Neptune to get right order of magnitudish - gave me a rough mental location and also chance of there being a selfy with sun from Voyager round Neptune

kzt wrote:That suggests that when the other star is visible you’ll have something like 10 lux everywhere, which is twilight level brightness, vic 40 times as bright as a full moon.

That's only considering Manticore-B, alone, at close to apoastron. If full Thorson is also up in the sky, it'll be brighter.

Manticore-A, 20% brighter than a G2, at periastron (21% closer) would make it 40 * 1.2 * (1.21)² = 77x brighter than a full moon in the skies of Gryphon.

Quite true, but there are reasons to suspect that this isn't a normal system. The outer planetary orbits shouldn't be stable, and the spectral classes and masses given suggest that there's a several-billion year difference in the ages of the stars.

And even for "normal" systems it turns out that the assumption of coplanarity is flawed because of the complexities of the gravitational interactions between the various massive planets as the system evolves through it's first couple of hundred million years. Simulations suggest that the ecliptic can end up tilted rather strongly to the axis of rotation of the star, and there's no reason to expect the tilt to be the same for the Man A & B systems. ISTR seeing something to the effect that turbulence effects can lead to the spins of the individual stars not being parallel to the orbital momentum as well, but I'd have to go digging to be sure that I'm remembering that bit correctly.

ThinksMarkedly wrote:

Rowbi wrote:If we assume that the stars orbit one another in close to the same plane as the their planetary systems. Wouldn't that mean that for at least part of the year the other Star would rise and set during planetary night.

They usually do, since they're usually formed from the same molecular cloud and retained the angular momentum that the cloud possessed. Binary systems due to capture are possible, but a G2 / G0 pair capture is anywhere between unlikely to impossible. One of the two stars would need to be far more massive than the other -- capturing red dwarfs, for example.

So yes, there's a day in the year when both stars rise at the same time and there's another in which one rises when the other sets. The time between those two events is not exactly half a year because the two stars are moving relative to one another.

And because it's going to be very close to the ecliptic on either system, it's not very useful for land-based navigation. And it does move relative to background stars, albeit very slowly.

Louis R wrote:Quite true, but there are reasons to suspect that this isn't a normal system. The outer planetary orbits shouldn't be stable, and the spectral classes and masses given suggest that there's a several-billion year difference in the ages of the stars.

I agree on the orbits of the outer planets, but why are you saying that the stars can't have roughly the same age? Nothing prevents a G0/G2 pair, so you must be thinking of some more information.

Were the masses of the two stars ever given, not just their spectral classes? Or are you calculating that from the Manticore and Gryphon year lengths and their orbital radii?