How to draw longitudinal lines on a circle as Earth?

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Discussion Overview

The discussion revolves around the method of drawing longitudinal lines on a circle that represents Earth, specifically focusing on how to measure and mark these lines at 15, 30, and 60-degree intervals. The scope includes conceptual understanding and practical application of geometry and trigonometry.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to measure angular distances for drawing longitudinal lines on a circle representing Earth.
  • Another participant questions whether the representation is of a circle or a sphere, suggesting that the equator may imply a spherical model.
  • A different participant clarifies that the angle for longitude is measured at the center of the Earth, providing a conceptual framework involving points on the equator and lines extending north.
  • One suggestion involves projecting a line from the center of the circle and rotating it to mark the longitudinal lines, indicating that the intersection with the circle defines the longitude.
  • Another participant highlights an approach of visualizing the sphere from above and projecting points onto the circle without needing an additional circle for reference.
  • A final participant expresses gratitude for the assistance received, indicating that the responses were helpful.

Areas of Agreement / Disagreement

Participants present various methods and conceptualizations for drawing longitudinal lines, with no consensus on a single approach. There are differing views on the representation of Earth as a circle versus a sphere, and the methods for measuring and marking the angles are not universally agreed upon.

Contextual Notes

The discussion does not resolve the assumptions regarding the dimensionality of the representation (circle vs. sphere) or the specific mathematical steps required for accurate drawing.

Nargis Adham
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I have a circle, representing Earth with equator drawn on it. I need to draw longitudinal lines on 15 degree, 30 degree, and 60 degrees distance? I am not sure how and from where to measure these angular distances. Thanks.
 
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How did you draw an equator on a circle? Do you mean a sphere?

These may help.
https://www.google.co.nz/search?q=l...ChMI3KjJlpzrxwIVRRamCh00bwXM&biw=1680&bih=925

And this:

picture-s=r-theta-circle.gif
 
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Nargis Adham said:
I have a circle, representing Earth with equator drawn on it. I need to draw longitudinal lines on 15 degree, 30 degree, and 60 degrees distance? I am not sure how and from where to measure these angular distances. Thanks.
The Earth is a ball. The angle is measured at the center of the Earth.

Imagine a point X on the equator. Imagine a line going directly north from that point. Imagine a point Y somewhere on that north-going line.

Imagine a line x between point X and the center of the Earth. Imagine a line y between point Y and the center of the Earth. There is an angle between the two lines. That's the measure of longitude.

To figure out where to draw the line of longitude in your circle on paper, you will need trigonometry.
 
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Project a line from the center of the circle straight down. This is 0 degrees.
Rotate this line left or right 15 degrees, place a vertical line where it intersects the circle. Where this vertical line intersects the equator is where the longitude is.
Repeat for 30, 60 degrees.
If you want to draw in the entire longitude you'd have to draw parts of an ellipse.
long.gif
 
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What scientific601 is demonstrating is that you can start by drawing the sphere looking down on it from above. Then project those points to the face.
longitude.png
scientific601 has eloquently done it without needing to use an extra circle.
 
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Thank you so much everyone for your help and your time. Your answers are very helpful for me. Thanks again!
 

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