Celestia Forums

What is the best calculator for converting time units for use in Celestia?
I have tried several, needing to convert years to hours, but different ones do not give the exact same results, and over a period of thousands of years the discrepancy becomes too big to be practical.

I need to compute a stable relationship between two bodies for about 6000 years.

A web-based utility would be optimal... Alternately a win or OSX app.

-rthorvald

rthorvald wrote:What is the best calculator for converting time units for use in Celestia?
I have tried several, needing to convert years to hours, but different ones do not give the exact same results, and over a period of thousands of years the discrepancy becomes too big to be practical.

What kind of years? (Julian, Gregorian, tropical, sidereal, anomalistic, ... )

- Hank

rthorvald, something like this?

Or what else?
Bye

Andrea

Ot this one?
Bye

Andrea

I brought this up in an earlier post http://www.shatters.net/forum/viewtopic.php?t=8001

there is a link there to a freeware converter...

ANDREA wrote:http://www.onlineconversion.com/time.htm[/code]

Yes, this is the one i normally use. But how exact is it? It gives one terrestrial year as 8760 hours, while a time converter that came with my OS gives 8766 hours. What i am looking for is really a formula that matches how Celestia measures time...

-rthorvald

rthorvald wrote: What i am looking for is really a formula that matches how Celestia measures time... -rthorvald

Perhaps this page

will give you the answer you need (but, alas, there is more than one, as you'll see).
Hope this will help.
Bye

Andrea

rthorvald wrote:

ANDREA wrote:http://www.onlineconversion.com/time.htm[/code]

Yes, this is the one i normally use. But how exact is it? It gives one terrestrial year as 8760 hours, while a time converter that came with my OS gives 8766 hours. What i am looking for is really a formula that matches how Celestia measures time...

-rthorvald

An ordinary year is 8760 hours (365 days * 24 hours). A leap year is 8784 hours (366 days * 24 hours). An average year (with 1 out of 4 years a leap year) is 8766 hours (365.25 * 24 hours).

Can you give us a better idea of what you're trying to do? Are you sure Celestia itself has the required precision?

- Hank

hank wrote:An average year (with 1 out of 4 years a leap year) is 8766 hours (365.25 * 24 hours)

Well, i have assumed that this is what Celestia takes to be one year.

hank wrote:Are you sure Celestia itself has the required precision?

No, that is what i am trying to find out.

hank wrote:Can you give us a better idea of what you're trying to do?

Spesificially, i have a planet with a period of 0.3450137 years. I am trying to align this with the rotationperiod of the star, so that it passes a certain spot on the star surface at spesific dates - but over time it drifts off. I don??t know if it is the calculator or Celestia yet.

-rthorvald

rthorvald wrote:Specificially, I have a planet with a period of 0.3450137 years. I am trying to align this with the rotationperiod of the star, so that it passes a certain spot on the star surface at spesific dates - but over time it drifts off. I don??t know if it is the calculator or Celestia yet.

-rthorvald

From the code it looks like Celestia uses years of 365.25 days for the orbital period and 24 per day hours for the rotation period. I'd guess your problem is due to imprecision in the math calculations.

- Hank

hank wrote:From the code it looks like Celestia uses years of 365.25 days for the orbital period and 24 per day hours for the rotation period. I'd guess your problem is due to imprecision in the math calculations.

Thank you.

- rthorvald

++++++++++++++++++++++++
Since you happen to talk about Celestia's precision, there is a known typo in Celestia, concerning the numerical value of the speed of light.

The astrophysical consequences of this slightly incorrect value have so far not been explored. They could be significant notably on long time scales.

We have not yet replaced the value by the correct one, since this would invalidate a number of existing stuff, like CEL://urls .This issue definitely calls for a clean solution!

+++++++++++++++++++++++++

Cheers,
Bye Fridger

t00fri wrote:We have not yet replaced the value by the correct one, since this would invalidate a number of existing stuff, like CEL: urls.

Wasn't there a change in the universal coordinate system in 1.4.0 that also invalidates CEL: urls? So that perhaps now is the time to make this fix?

- Hank