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# The blue marble

jim7
Hi frihost forum,

A simple doubt?.
From Wikipedia:

1. The earth- "Blue Marble"- The "snapshot"—taken by astronauts on December 7, 1972- This picture is a circle, a PERFECT circle.
2. Figure of the earth- An oblate spheroid, may be very close to a sphere.

Why the difference. If the earth's shape is not a perfect sphere but very close to a sphere, there is no way that snapshot "Blue Marble" can be a perfect circle.
Any explanation for this difference?
Ankhanu
Photography is a 2D medium so, yeah, it's a circle.
The amount of bulge and flattening is extremely slight; yes it's measurable, but at the scale of the whole planet it is incredibly insignificant. The amount of bulge that would be significant enough to see visually from space would cause the entire equatorial region to be flooded with ocean tides every day... which clearly doesn't happen.
kelseymh
 jim7 wrote: Hi frihost forum, A simple doubt?. From Wikipedia: 1. The earth- "Blue Marble"- The "snapshot"—taken by astronauts on December 7, 1972- This picture is a circle, a PERFECT circle.

No, it's not perfect. You just can't tell.

 Quote: 2. Figure of the earth- An oblate spheroid, may be very close to a sphere. Why the difference. If the earth's shape is not a perfect sphere but very close to a sphere, there is no way that snapshot "Blue Marble" can be a perfect circle. Any explanation for this difference?

Why don't you apply some quantitative reasoning to your question? The equatorial diameter of the Earth is 12756.2 km, while the polar diameter is 12713.6 km. Suppose you print out the Blue Marble picture so that it is exactly 20 cm wide (equatorial diameter). How tall (polar diameter) will it be? Can you see that difference by eye? Can you measure it with a regular ruler (1 mm scale)?
BigGeek
If I am not mistaken the reason the planet looks like a perfect circle from space is because the atmosphere hides all the inconsistencies and irregularities of the spheroid shaped earth.