Radius of Earth at specific angle,

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SUMMARY

The discussion focuses on calculating the radius of the Earth at various latitudes using the formula provided in a Wikipedia article. The radius at the Equator is approximately 6,378.137 km, while at the poles it is about 6,356.7523 km. The formula to calculate the radius at a given latitude (φ) is R = √[(a²cos(φ))² + (b²sin(φ))²] / [(acos(φ))² + (bsin(φ))²], where a and b are the semi-major and semi-minor axes of the Earth, respectively. Participants provided examples for specific latitudes, such as 61° and 34°, demonstrating the calculation process.

PREREQUISITES
  • Understanding of basic trigonometric functions (sine and cosine)
  • Familiarity with the concept of geodetic latitude
  • Ability to perform calculations using a scientific calculator
  • Knowledge of the Earth's semi-major (a) and semi-minor (b) axes
NEXT STEPS
  • Learn how to apply the radius formula for different latitudes
  • Explore the implications of Earth's shape on geodesy
  • Study the differences between geodetic and geocentric coordinates
  • Investigate the impact of Earth's radius on navigation and mapping
USEFUL FOR

This discussion is beneficial for students, educators, and anyone interested in geodesy, geography, or Earth sciences, particularly those seeking to understand the mathematical calculations related to the Earth's radius at various latitudes.

TheJere
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I was going to post this on Earth-forum here but I thought that you guys here can help me better with this. I'm trying to get the radius of Earth on every latitude degree from 0° to 90°, knowing 0° at Equator is ~6378,137km and 90° at North/South Pole is ~6356,7523km (source Wikipedia). In Wikipedia there is formulas to calculate radius at any angle, but I don't have a clue how to calculate with it. Now to what I'm asking here:
Can someone please explain to me (one that doesn't have even College education on mathematics) so that I could understand it? Best way to explain would be adding some examples like for 61° and 34°?

Now, I have been struggling with this for a very very long time, and I am already being really thankful for the one that explains this to me.

Wikipedia article:
http://en.wikipedia.org/wiki/Earth_radius#Radius_at_a_given_geodetic_latitude
 
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No college math needed here, just how to use a calculator! The applicable formula is the first:
"The distance from the Earth's center to a point on the spheroid surface at geodetic latitude"
R= \sqrt{\frac{(a^2cos(\phi))^2+ (b^2sin(\phi))^2}{(acos(\phi))^2+ (bsin(\phi))^2}}
And you are given that a= 6,378.1370, b= 6,356.7523.

So if, for example, \phi= 61^o, cos(\phi)= cos(61)= 0.4848096 and sin(\phi)= sin(61)= 0.8746197.

So a^2cos(\phi)= 19722361, b^2sin(\phi)= 35341895, acos(\phi)= 3092.182, and bsin(\phi)= 5559.741 where I have rounded to 7 significant figures. Can you finish?
 
I'm afraid and really sorry, but I think I can't finish, haha. I put numbers you had calculated on formula and I keep having number 435114,36..., double-checked. Thank you very much for the your explain this far, I get it to the point you have calculated it, but I'm afraid I have to ask you to tell me how to finish it?
 
Oh, now I got it right, THANK YOU very very much, I'll be thankful for you for really long time!
 

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