Questions on moonar orbits and visability of planetary bodies

[TothAval]

Hi folks,

 

i have some questions i need answered for a story i am currently wrighting. I could probably do some digging and calculating myself, but i haven't done something like that in regards to astronomy for more than 15 years, so it would take me a lot of time, create a lot of frustration and would hinder me to proceed with my project. And the questions are quite hypothetical, so i would need to study the knowledge to get some deeper of understanding on the matter, which would also be time consuming, frustrating and an obstacle to finish the project. Therefor i hope some of you are professionals in the necessary fields and could answer me my questions with ideally no more effort than typing the answers into this thread. If i ultimately finish my project and you happen to stumble upon it and read it, than your reward would be some plausibility in the world building, at least in that area. I hope this is sufficient enough  

I myself adore plausibility and i hope i could achieve atleast some degree of it in my science fiction/fantasy world. The answers to the questions below are important for the atmosphere (yes, pun intended) of my setting  and the pictures i intend to paint in the mind of my future readers.

(additional questions i deem less important in parentheses)

 

Question 1:

Could an atmospheric reflection of sunlight be strong enough to ligthen up another atmospherical body to be visible for the naked eye?

My story takes place on a moon with an atmosphere surrounding a hot jupiter, which happens to be in the habitable zone around its sun. I assume the sun is similar to ours, since i do not intend to describe its light in a special manner. The gas giant has an atmosphere composed mainly of cyan/turquoise clouds, which are soaked with much smaller bits and stripes of yellow and violet, mainly to the pols. 

Now if i am standing on the moon during daytime and the sun is behind that gas giant, could i see the gas giant in daylight due to atmospheric reflection of the moons atmosphere or not?

(How close would the moon have to be so it would be possible, in case it could be possible?)

 

Question 2:

Can two plutoid sized bodies share the same orbit in opposition to each other around a gravitational centre?

I would like to have two moons separated by 180° on their orbital path around the gas giant. I am not asking if this could naturally occur, this is irrelevant for my purpose. I just need to know if this could be possible.

I guess so, but i am not a hundred percent certain.

(How would the movement of those moons appeal to a viewer on the surface of the atmospheric moon? How would the movement of other moons around the gas giant appeal in general? I have trouble imaginating it)

 

Question 3:

The monthly calendar on my place of action is based on the revolutions around the gas giant, so every 34 days my moon revolvs around the gas giant. The year is defined by the revolution of the gas giant around its star.  Now for reasons  (love this non-argument) i want to have it so, that the gas giant blocks, dimms, obstructs or whatever the sunlight for 17 days twice a year in manner, that these time periods are much darker than in comparison to the rest of the year. The second dark semi month would define the end of the old year and the beginning of the new one. So these two halfs of a month need to be considerably darker than a "normal" half. I am aware of the fact, that it can only become darker once the moon is entering the gas giants shadow, which would take some "days"(on my moon ), once it passes the orbital path towards the night side of the gas giant.  

Question is, could an orbital path be possible, that allows for such an behaviour? Again, not relevant if it could occour naturally. The whole system could be engineered, as far as i know so far  

This would mean, that i have a revolution around the gas giant, which would block the suns light to an lesser extend for 5 months in a row, while twice a year due to distance , orbital inclination or whatever the passage behind the gas giant would be much darker due to an increased obstruction of sunlight. 

 

Question 4: 

How dark could it get if you are on the dark side of a hot jupiter if there is a solar eclipse? How dark will it get on a normal day(see also question 3)? Will sunlight be redirected through the hot jupiters atmosphere or will i just have the light of the stars and the other moons, once i am in the umbra? 

 

Question 5:

How bright will such a hot jupiter be during night? As i see it there are three cases.

Case one: moon is in direction of the star and the gas giant is fully reflecting the sun light. (i currently handle this as if it were almost as bright as daylight, at least considerably more brighter than a fullmoon on earth. The world is than colored in the dominating color of the gas giants atmosphere, would this be correct?)

Case two: moon is on the dark site and the gas giant is ...? (see questions 3 and 4)

Case three: moon is on or near the orbital path of the gas giant. So you would see at least one half of it during night and also during day. 

 

Question 6:

Would a ring system around the gas giant be of any effect to the questions above?

 

Question 7:

How big would such an gas giant occour on the sky, considering there is an orbit around it, which allows for the desired effect of question 3?

 

Don't know how difficult these will be to answer. If you need any more information to answer these questions, i will be happy to provide what i have thought of so far. 

 

 

Edit: Non-native speaker, if something is unclear, please feel free to ask. I will try to clarify.

 

Edited November 12, 2016 by TothAval

[cantab]

1. If the view of the Sun is actually blocked, well that's an eclipse, and here's one of Saturn taken by a space probe. Depending on the orbits this could happen every time the moon goes round its planet, or it could be rarer.

If the view of the Sun is not blocked, well that's a crescent planet. Considering that the Moon is easily visible by day from Earth when it's up, unless the crescent is extremely thin, a gas giant of similar or larger apparent size would be no problem.

2. They won't stay 180 degrees apart, but will drift. Now it is possible for the arrangement to be stable in the long term, as seen with Janus and Epimetheus orbiting Saturn. At any given time one is in a slightly lower and thus slightly faster orbit and slowly catches up, but when they get close their gravity interacts to effectively swap orbits, the one that was faster is now slower and drifts away, before eventually being caught the other side and the process repeats.

As for what it would look like, from one of the moons its co-orbital partner would keep a nearly constant apparent separation from the planet. In the case of Janus and Epimetheus their orbital periods are each about 0.6 days and it takes 4 years (Earth) for them to complete a cycle.

3. It's straightforward, and indeed quite natural, for eclipses to only occur twice for every year (roughly) of the parent planet. That's how it is for Earth and Moon. It's harder to make those eclipses last half a month though.

4. There would almost surely be light scattered through the atmosphere of the planet. For Earth and Moon, the Moon is clearly visible when it's eclipsed and furthermore appears brighter than when it is lit by Earthshine. It's likely to be the same for your planet and moon - "Eclipse days" will be dark compared to normal days, but possibly brighter than a gas-giant-lit night and much brighter than a gas-giantless night. That said, a lot depends on the atmosphere of the gas giant, perhaps a certain composition and structure would make eclipse days very dark.

5. Depends greatly on the apparent size of the gas giant. With the moon's orbital period fixed, that in turn will depend mainly on the gas giant's mass which will set its own size and the moon's orbital radius. It also depends on the gas giants albedo which could be anything from about .1 to .8 assuming the moon has Earthlike climate. Note that even the low .1 value is higher than Earth's Moon, so a gas giant at night is likely to appear pretty bright.

[TothAval]

Cool, thx for your answers. How can i give you any rep? Wasn't really active for quite a while on these forums.

[cantab]

You've done it, the new forums call it "Likes" not "Rep".