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cmatei

23 Ian 2013 15:32


radius vector vs. distanta soare-corp

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Poate exista vreo diferenta subtila intre cei 2 termeni, in contextul problemei celor 2 corpuri ?


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Andi

24 Ian 2013 15:40



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Unul poate fi vector, celălalt poate fi scalar.


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cmatei

26 Ian 2013 13:45



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Scalari amandoi (distanta). http://libnova.sourceforge.net/group__elliptic.html


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Doru Dragan

24 Feb 2013 12:49



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Distanta este scalar dar "radius vector" nu reprezinta distanta ci pozitia fata de un punct (in cazul asta Soarele).


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cmatei

24 Feb 2013 15:31



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Multumesc de raspuns, acum ca recitesc observ ca am omis mici parti esentiale din enunt, imi cer scuze :-) 

Incercam sa scriu un programel de generat efemeride pentru asteroizi, folosind libnova (o biblioteca de calcule astronomice), si am descoperit ca valorile returnate pentru elongatie si faza sunt gresite. Am gasit buba, ca sa repar imi trebuia distanta soare-corp, dar pentru ca stiu si eu diferenta totusi intre o pozitie si o distanta, m-au nedumerit numele functiilor.

In [url=http://libnova.sourceforge.net/group__elliptic.html]libnova avem:

double 	ln_get_ell_body_solar_dist (double JD, struct ln_ell_orbit *orbit)
 	Calculate the distance between a body and the Sun. 

double 	ln_get_ell_radius_vector (double a, double e, double E)
 	Calculate the radius vector. 

Evident, radius vector nu e nici un vector aici (pozitie). Par sa faca acelasi lucru, valorile fiind numeric egale pentru cele cateva orbite pe care am testat. Le-am trimis un patch, dar vad ca a ramas in coada de peste momentan.


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nobody

24 Feb 2013 21:13



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Nu toti programatorii sunt astronomi. Iar reciproca e valabila  :wink:

Poate confuzia vine din definita nestiintifica:
Definition of RADIUS VECTOR
1 a : the line segment or its length from a fixed point to a variable point
   b : the linear polar coordinate of a variable point
2 : a straight line joining the center of an attracting body (as the sun) with that of a body (as a planet) in orbit around it 

Desi matematic vorbind:
In geometry, a position or position vector, also known as location vector or radius vector, is a Euclidean vector which represents the position of a point P in space in relation to an arbitrary reference origin O. Usually denoted s or r, it corresponds to the displacement from O to P

Ce returneaza functia este: return a * ( 1.0 - e * cos (ln_deg_to_rad (E)));

Adica exact:
Thus, the radius (distance from the focus to point P) is related to the eccentric anomaly by the formula 
r = a ( 1 - e cos E) . http://en.wikipedia.org/wiki/Eccentric_anomaly#Radius_and_eccentric_anomaly


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cmatei

24 Feb 2013 22:29



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1 a : the line segment or its length from a fixed point to a variable point

Superb, mersi. Nu m-am intalnit cu definitia/utilizarea asta.


Adica exact:
Thus, the radius (distance from the focus to point P) is related to the eccentric anomaly by the formula 
r = a ( 1 - e cos E) . 

Pai da, parea ce trebuie cu cartea-n fata :-) dar am zis ca poate imi scapa mie ceva.