Distance to Mars: Earth-Mars Equation for Moon-Sized Mars View

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Discussion Overview

The discussion revolves around calculating the distance from Earth to Mars required for Mars to appear the same size as the Moon when viewed from Earth. Participants explore mathematical approaches and concepts related to angular size and similar triangles, while also touching on the Moon illusion as a related phenomenon.

Discussion Character

  • Mathematical reasoning
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant queries the distance at which Mars would appear the same size as the Moon, suggesting that research is needed to determine the Moon's diameter as viewed from Earth.
  • Another participant calculates that Mars would need to be approximately 750,000 km away to appear the same size as the Moon, based on their diameters and the Moon's average distance from Earth.
  • A participant suggests using a triangle to illustrate the relationship between the distances and sizes of the Moon and Mars.
  • It is noted that the concept of "similar triangles" can be applied to simplify the calculations, although the actual triangle may not be a right triangle.
  • Further calculations are provided to compare the angular sizes of the Moon and Mars, indicating that Mars would not come close enough to appear the same size as the Moon.
  • One participant introduces the Moon illusion, explaining that it is an optical illusion where the Moon appears larger near the horizon, which may relate to the discussion on perceived sizes.

Areas of Agreement / Disagreement

Participants generally agree on the calculations regarding the distance needed for Mars to appear the same size as the Moon, but there is no consensus on the feasibility of Mars ever being that close. The discussion also introduces the Moon illusion, which adds another layer of complexity without resolving the main query.

Contextual Notes

The calculations depend on specific assumptions about distances and diameters, and the discussion does not resolve the implications of the Moon illusion on perceived sizes.

Scrythe
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Hey guys, With that rumor around the internet that Mars will look as big as the moon, i was wondering how far the Mars would be from the Earth for it to really look that big.

show an equation that shows the distance from Earth to Mars where Mars would have the same diameter as the moon, when viewed from earth. I guess some research would be involved to find the diameter of the moon when viewed from earth.

-Scrythe
 
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Moon:
Distance = 385,000km
Diameter = 3500km

Mars:
Diameter = 6800km

Distance Mars would have to be at to appear same size as moon
=(6800km/3500km) * 385,000km = 750,000km

Closest approach of Mars to Earth = 55,758,000km
 
hmm...seems easier than i thought. Thanks for the quick reply.

Is there any way to show this using a triangle?
 
Scrythe said:
Is there any way to show this using a triangle?
Yes.
 
That's actually what he did - the mathematical concept is "similar triangles": http://www.gcseguide.co.uk/similar_triangles.htm

You are at one point of the triangle, the moon or Mars is at the far side and the two big sides are the distance. They aren't really making a right triangle, but you can assume it to make the calculation easier if you want.
 
mgb_phys said:
Moon:
Distance = 385,000km
Diameter = 3500km

Mars:
Diameter = 6800km

Distance Mars would have to be at to appear same size as moon
=(6800km/3500km) * 385,000km = 750,000km

Closest approach of Mars to Earth = 55,758,000km

Moon angular size of diameter = (3.5/385) * 180deg/pi = 0.52 deg
Mars angular size of diameter = (6.8/55,758) * 180deg/pi = 0.0070 deg

To truly do it, you need a solid angle, but you get the picture.
 
cool, thanks guys
 
While the calculations show that Mars will never be so close as to appear the same size of the Moon, a matter--which comes to mind---and, perhaps, related to this discussion is the Moon illusion:

The Moon illusion is an optical illusion in which the Moon appears larger near the horizon than it does while higher up in the sky. This optical illusion also occurs with the sun and star constellations. It has been known since ancient times, and recorded by numerous different cultures.

Wikipedia has a long article on this.
 

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