# Stargazing Sun, Moon and Earth

#### Damned2Hell

Could you prove to me how one might calculate things like mass, gravity, distance, of the sun, moon and Earth, very quickly, with only some basic knowledge. Such as 365.25 per year, min, avg and max times for the moon to complete a lunar phase 29.26,29.53,29.8). I'm attempting to understand how ancient people may have found those answers. But I'd like to know the best methods, to figure out older possible methods more quickly. If you don't know what I'm getting at with the included estimates, 29.26/29.8= 0.98187, a close estimate of Earth's gravity. While it's easy enough to see the relationship with a few calculations, I'd want to understand how to make the calculation without having read gravity is 9.807 m/s^2. And to build on that understanding, for other calculations.

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#### phinds

Gold Member
What research have you done on this so far? What have you found out?

#### Damned2Hell

I know a lot as far as knowing there are a lot of numbers that are very closely related. As far as being able to look at the min and max times from lunar phase to lunar phase and know I could calculate gravity, I can't. What made you ask what I know, is it something you're studying?

#### lomidrevo

Could you prove to me how one might calculate things like mass, gravity, distance, of the sun, moon and Earth, very quickly, with only some basic knowledge.
Be more specific with your question. What particularly do you not understand?
Hint: observations, Newton's laws and trigonometry are you best friends to find the answers.
Such as 365.25 per year, min, avg and max times for the moon to complete a lunar phase 29.26,29.53,29.8). I'm attempting to understand how ancient people may have found those answers.
Why do you think that ancient civilizations managed to calculate mass of the celestial bodies, or that
they found laws describing the gravity? Use google to read about history of astronomy, there are plenty of texts out there.
If you don't know what I'm getting at with the included estimates, 29.26/29.8= 0.98187, a close estimate of Earth's gravity.
This looks like numerology! You cannot calculate gravitational acceleration at the Earth's surface just by dividing observed lunar periods!

#### Drakkith

Staff Emeritus
2018 Award
If you don't know what I'm getting at with the included estimates, 29.26/29.8= 0.98187, a close estimate of Earth's gravity.
Nonsense. It's an order of magnitude off if you're using meters and seconds. The fact is that your estimate is just close to 1 because the Moon doesn't have much variation in its orbit. Earth's gravitational acceleration could be literally anything and your number wouldn't change much as long as the Moon's orbit was stable.

#### phinds

Gold Member
I know a lot as far as knowing there are a lot of numbers that are very closely related. As far as being able to look at the min and max times from lunar phase to lunar phase and know I could calculate gravity, I can't. What made you ask what I know, is it something you're studying?
Because this is not a Q&A forum. We expect people to have put in some effort themselves, and to show it, as part of asking a question. We don't just do your research for you.

#### Orodruin

Staff Emeritus
Homework Helper
Gold Member
2018 Award
Agreed. The ultimate sign of this being that the numbers do not even have the same physical dimension. ”Nonsense” is fully appropriate.

#### berkeman

Mentor
And since this new user has now taken the "Down Elevator" for some issues in a different thread, this thread here can be closed. Thanks for your helpful replies, folks.

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