A comet, which was seen for last time fifty thousand years ago by neanderthals, it's coming back tos returning and can be seen on the days 1st and 2nd of February.

I would like to see it but I don't know if that it couldit might be possible b. Because, where I live there's so much light pollution (like in almost every country).

I really would like to see it because this comet won't pass Earth again aftuntil after another fifty thousand years.

Day 19: (The) Green Comet

This is very common in English; we will usually use a definite article in a title of an object ! E.g. “The Burglar” “The Park”

A comet which was seen for lathe first time by Neanderthals fifty thousand years ago by neanderthals it's coming back to be seen the days 1st and 2ndwill be reappearing on the first and second days of February.

- I am not sure about the context of the first sighting of the comet but I am just going to assume that it has only ever been seen once; (let me know if it wasn’t!) we would refer to it as ‘the first time’.
- ‘it’s is coming back to be seen’ can just be shortened to ‘it will be reappearing’
- the word order in relation to ordinal numbers and days; “it was her first day of school” “it was the last day of school” we always put the ordinal/context of the day at the start

I would like to see it but I don't know if that it couldit will be possible because where I live, like in almost any other country, there'’s so much light pollution (like in almost every country).in my city/town.

- the use of the conditional tense with ‘could’ does not suit here, as you are referring to the future and an exact fact/assumption, you would say ‘will’.
- the way I’ve put it sounds much more natural. The saying is as goes: “like in any other town” “like for any other person” etc.!

I don't know how it will look in the sky, I never have seen something like thisbecause I’ve never seen it before.

- there is no need to clarify ‘in the sky’ as we assume the comet will remain in the sky/appear in the sky !
- you would use ‘because’ here, due to the fact that you are justifying your opinion (that you don’t know what the comet will look like) with the fact that you’ve never seen one before !
- we wouldn’t use ‘this’, we would say ‘it’ or ‘one’! However:
> if you used ‘one’, it would mean that you’ve never ever seen a single comet before
> if you used ‘it’, it would mean that you have never seen this particular comet in your life before.

I really would like to see it because this comeit won't pass Earth again aftfor another fifty thousand years.

“I won’t see her for another ten days.”
“She’ll be staying at my house for another two weeks.”

Day 19: The Green Comet

A comet which was seen for last timeseen fifty thousand years ago by neanderthals it's coming back to be seen the days 1st and 2nd Februaryand will be visible February 1 and 2.

また、

A comet which was last seen fifty thousand years ago by neanderthals is returning to Earth and can be seen February 1 and 2.

I would like to see it but I don't know if that it could bes possible because where I live there's so much light pollution (like in almost every country).

そうですね。

I don't know how it will look in the sky, because I never have seen something like this before.

私たちは全員若すぎますね。

I really would like to see it because this comet won't pass by Earth again aftfor another fifty thousand years.