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General => Terragen Discussion => Topic started by: TheBadger on December 21, 2013, 03:50:07 PM

Title: Real distance of the Moon and Planet02
Post by: TheBadger on December 21, 2013, 03:50:07 PM
Hello,

I'm just a little confused about the default position of the planet02 object.

I was playing around, and decided to put the real numbers in the distance parameter for the the object as the earth moon.
Google says the distance of the moon from the earth is; 238,900 miles or 3.84472e8 meters.
The help button in TG says the moon has a radius of 1738000 m

BUT

If you put a planet02 with a radius of 1738000 m and a distance of 3.84472e8 meters, it just does not look right. The moon is so small in the sky that its hardly visible at all. Its certainly nothing like we see in images in these forums. Its not even the size I see in reality, in the sky above my house anyway.

So what am I getting wrong here?

Thanks.
Title: Re: Real distance of the Moon and Planet02
Post by: Upon Infinity on December 21, 2013, 04:06:53 PM
The fact that Planet02 (in its default configuration) was never meant to be a real interpretation of the actual moon to the actual earth.

There could be a discrepancy between how the moon is measured (whether from the centre of the earth or the surface) to how Terragen measures planets that are removed from itself (from the centre or from the surface).  Also, factor in your own relative perception, which changes, as well.  Sometimes, the moon seems bigger at the horizon and smaller at the zenith.  Also see: I just don't know.
Title: Re: Real distance of the Moon and Planet02
Post by: bobbystahr on December 21, 2013, 09:56:28 PM
This be a query for Matt or Jo methinks, and one that has passed thru my mind as well.
Title: Re: Real distance of the Moon and Planet02
Post by: TheBadger on December 22, 2013, 04:20:22 PM
Yes, I would like to hear from them, but Im more curious than anything. Obviously we can all fake it pretty well, the look of the moon in the sky I mean.
Having things exactly as in reality can be pretty fun though.

Title: Re: Real distance of the Moon and Planet02
Post by: bigben on December 23, 2013, 07:02:59 AM
The angular diameter of the moon is only 29.3′ – 34.1′, similar to that of the sun (31.6′ – 32.7′)  It's small. I used the real dimensions for my moon model and it looks OK, i.e. you need a narrow fov to see any detail.
Title: Re: Real distance of the Moon and Planet02
Post by: TheBadger on December 23, 2013, 11:44:01 AM
Thanks for an answer on this big ben. Its a little tricky.

Title: Re: Real distance of the Moon and Planet02
Post by: bigben on December 23, 2013, 03:21:20 PM
It is interesting how we perceive the moon.  We don't hear anyone complaining that the sun is too small/big (OK, with the possible exception of sunsets). In both cases though people think of photographs shot with 200mm (or longer) lenses but expect it to look like that when they use a render camera the equivalent of 24-50mm.
Title: Re: Real distance of the Moon and Planet02
Post by: Upon Infinity on December 23, 2013, 04:22:36 PM
Quote from: bigben on December 23, 2013, 03:21:20 PM
It is interesting how we perceive the moon.  We don't hear anyone complaining that the sun is too small/big (OK, with the possible exception of sunsets). In both cases though people think of photographs shot with 200mm (or longer) lenses but expect it to look like that when they use a render camera the equivalent of 24-50mm.

Yeah, I thought about that, too.  I ran Badger's numbers and changed the camera to a 50mm (standard human FOV), and it still seemed a bit small.  So I chalked it up to just being to how the distance is measured.
Title: Re: Real distance of the Moon and Planet02
Post by: bigben on December 23, 2013, 05:23:05 PM
FWIW the default angular diameter of the sun in TG is 0.5° making it some 50% bigger than it should be  ;)
Title: Re: Real distance of the Moon and Planet02
Post by: TheBadger on December 23, 2013, 06:24:52 PM
^^ Its just funny. IF you told me 18 or 19 years ago that I would spend even my free time thinking about these things, I would have thought you were high too.
Title: Re: Real distance of the Moon and Planet02
Post by: Matt on December 24, 2013, 06:14:12 AM
+1/like on Ben's explanations :)
Title: Re: Real distance of the Moon and Planet02
Post by: Matt on December 24, 2013, 06:15:07 AM
Quote from: bigben on December 23, 2013, 05:23:05 PM
FWIW the default angular diameter of the sun in TG is 0.5° making it some 50% bigger than it should be  ;)

How so? 30 arcminutes (from your earlier post) is 0.5 degrees.

Matt