How Bright Would a "Summer" Night Be on This Extreme Alternate Earth?

Question

Here is the oversimplified map of the solar system of an alternate Earth:

It is actually two separate binaries--one consisting of a red giant 100 times as wide, one-third as massive and 1,000 times as bright as our sun orbited by a yellow-white dwarf 130% as wide, 170% as massive and six times as bright as our sun; another consisting of two yellow dwarves, each one 105% as wide, 110% as massive and 126% as bright as our sun. This alternate Earth orbits the latter binary.

Here is the map of the alternate Earth.

And now here is the alternate Earth in comparison to our Earth:

Axial tilt is at 3.6 degrees, so the seasons in this world are defined by how many "suns" are in the sky at a certain point in the year. "Summers" are where you can see the red giant, the yellow-white dwarf and both yellow dwarves at once, creating daylight as bright as Venus and a night 1,000 times brighter than back home, whereas "winters" are where you can see only the yellow dwarves, creating daylight as bright as Mars and night only 60 times as bright as back home (courtesy of its location in a very dense star cluster.)

In the scope of a natural, panoramic landscape, how would a "summer" night 1,000 times brighter than our own compare to any natural light back home? (Chris Wayans compared it to "good indoor lighting" when creating the dry moon Tharn, but that comparison does not seem to fit the overall natural panoramic picture.)

Answer 1

I believe what is really being asked here is that you have a world which experiences Earth-like seasonal variations. It orbits one solar system, but is also heated by an adjacent solar system to experience Earth Like climate variations, based on it's own yearly orbit around it's parent stars.

Earth's Summer hemisphere averages about 303 Kelvin and our Winter Hemisphere averages about 283 Kelvin; so, in this star system, it means that the central stars will together contribute 93.4% of the solar energy hitting this planet, and the other 2 stars will only contribute ~6.6% of the its average solar energy.

So, this means that the night time on this world will be about 14 times darker than daytime during summer. Outdoor daytime lighting on Earth is normally about 3,000-18,000 Lux whereas indoor lighting is normally kept at only 200-500Lux. This means that your summer night sky will be about as bright as a well lit indoor room. The stars themselves will also be distant enough that they will appear significantly smaller than our sun, but much larger and brighter than night time stars. Looking straight at them will feel a lot like looking straight at a couple of 60watt light bulb from about 1 or 2 meters away.

That said ... there is Light and then there is Visible Light. Red and Blue stars emit more EM radiation that is outside of the human visible light spectrum; so, the Summer night sky may or may not appear darker than this depending on how far into the IR and UV spectrum your planet's organisms can see.

They will also affect the colors of things you see at night. Your 2 yellow suns will tint everything similar to how outdoor lighting tints things here on Earth, but a red and blue star will take away all of your greens and yellows allowing you to only see those two extremes of the visible light spectrum.

It's also important to note that eyes are very good at adjusting to different light conditions so being outside during the nighttime will not actually look much darker since your irises can just open up enough to make the nighttime light appear as bright as daylight and vice versa. This is why outside does not appear much brighter than inside to us humans here on Earth even though it actually is.

Answer 2

It is actually two separate binaries--one consisting of a red giant 100 times as wide, one-third as massive and 1,000 times as bright as our sun orbited by a yellow-white dwarf 130% as wide, 170% as massive and six times as bright as our sun; another consisting of two yellow dwarves, each one 105% as wide, 110% as massive and 126% as bright as our sun. This alternate Earth orbits the latter binary

A yellow-white dwarf should be equal to a spectral class F star, I guess. A star 130% as wide as the Sun would have 219.7 percent of the volume of the Sun, and if it had the same density it would have 219.7 percent of the mass of the Sun, not 170 percent.

The yellow dwarf stars with 105 percent the diameter of the Sun would have 115.76 the volume of the Sun, and thus its mass, instead of 110 percent the mass of the Sun.

You should check the physicial characteristics of various spectral types of stars in user177107's answer to the question:

https://astronomy.stackexchange.com/questions/40746/how-would-the-characteristics-of-a-habitable-planet-change-with-stars-of-differe/40758#40758[1]

The chart claims that:

A G5V star would have 0.98 of the Sun's mass, 0.982 of the Sun's radius, and 0.887 of the Sun's luminosity.

A G2V star would have 1.02 of the Sun's mass, 1.01 of the Sun's radius, and 1.014 of the Sun's luminosity.

A F8V star would 1.18 have of the Sun's mass, 1.25 of the Sun's radius, and of 2.031 the Sun's luminosity.

A F5V star would have 1.33 of the Sun's mass, 1.46 of the Sun's radius, and 3.434 of the Sun's luminosity.

A F2V star would have 1.44 of the Sun's mass, 1.61 of the Sun's radius, and 9.3 of the Sun's luminosity.

A A8V star would have 1.67 of the Sun's mass, 1.81 of the Sun's radius, and 14.392 of the Sun's luminosity.

I don't think that your figures for the diameters and massess and luminosities of the stars are quite correct.

A red giant star is one which has completed its main sequence period. In a star system where the stars are the same age, the most massive star will completed it smain sequence priod first and become a red giant star first. So I fail to see how the red giant could have one third the mass of the sun, and if it did it would orbit the yellow-white dwarf instead of being orbited by it.

A separation of 10 AU between the two pairs of stars seems insufficient to protect the "Alternate Earth" from a runaway greenhosue effect as the red giant becomes more luminous. A planet 10 AU from the Sun would recieve only 1 percent of the radiation from the Sun as a planet 1 AU from the Sun would receive. Yousay the red giant is 1,000 times as luminous as the Sun.

So the "Alternate Earth" 10 AU from the giant star would receive 10 times as much radiation from from the red giant as Earth receives from the Sun. That should be enough to cause a runaway greenhouse effect, destroying all life on the planet.

Remember that luminosity decreaes with the square of the distance. So if the absolute luminosity of a star in your system equals more than the luminosity of the Sun divided by the square of the distance in AU to a planet in that system, that planet will receive more radiation from that star than Earth gets from the Sun, and will thus be hotter than Earth.

Why do you write:

10 AUs, safe from the intense flares of the yellow-white dwarf.

As far as I know, some red dwarf stars o are the mainsequance stars with the most intense flares, which is why those red dwarf stars are known as flare stars.