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because of the position of your latitude on the earth, combined with earth's axial tilt.
The points on a crescent moon define a line perpendicular to the incidence of sunlight.
Viewed from the earth's equator at equinox, the Crescent always appears to be on the bottom, or the top, because at equinox the sunlight is perpendicular to your position on the equator.
However, on the same day, viewed from the north or south pole, the crescent moon would appear perfectly on its side, because the earth's axis is roughly aligned with the moon's.
As your position changes across latitudes, the angle of your horizon to the incident sunlight changes.
The earth's axis is tilted 23 degrees from being perfectly perpendicular to the sun's rays. And the moon's orbit around the earth is tilted relative to the earth's equator.
This creates a complex cycle of alignment between sunlight and your position on the earth. Thus, the crescent of the moon will appear to tilt depending upon where you are, what time of year it is and the moon's inclination to the earth.
Read more: http://wiki.answers.com/Q/Why_does_..._the_bottom_instead_of_the_side#ixzz21ZYwn7kI
The points on a crescent moon define a line perpendicular to the incidence of sunlight.
Viewed from the earth's equator at equinox, the Crescent always appears to be on the bottom, or the top, because at equinox the sunlight is perpendicular to your position on the equator.
However, on the same day, viewed from the north or south pole, the crescent moon would appear perfectly on its side, because the earth's axis is roughly aligned with the moon's.
As your position changes across latitudes, the angle of your horizon to the incident sunlight changes.
The earth's axis is tilted 23 degrees from being perfectly perpendicular to the sun's rays. And the moon's orbit around the earth is tilted relative to the earth's equator.
This creates a complex cycle of alignment between sunlight and your position on the earth. Thus, the crescent of the moon will appear to tilt depending upon where you are, what time of year it is and the moon's inclination to the earth.
Read more: http://wiki.answers.com/Q/Why_does_..._the_bottom_instead_of_the_side#ixzz21ZYwn7kI
