by Chris Peterson » Mon Mar 22, 2010 5:24 pm
owlice wrote:why does the local zodiacal dust show up as a wave? Rather, how it is that it is so well organized?
Anything that is linear on the sky- that is, lies on a plane containing the Earth, will show up as a sine-like curve on a wide field image mapped to a plane. The only exception is for objects that lie on the plane defining an inclination of zero in the data coordinates. Those objects will describe a simple line on the projection.
Imagine that you hold a hula hoop flat (inclination 0°) at eye level, and turn around inside it. Clearly it describes a line through the middle of your visual field. Now tip it (say, inclination 45°). Clearly, it will be low in your visual field when you are turned in one direction, high opposite that, and crossing diagonally through your field in between those two positions. If you were to plot the vertical position of the hoop at each angle of rotation, you'd get a sine curve.
On a very wide field astronomical image, the horizontal axis is usually the angle as the camera has rotated, and the vertical axis is the angle away from the plane of rotation.
[quote="owlice"]why does the local zodiacal dust show up as a wave? Rather, how it is that it is so well organized?[/quote]
Anything that is linear on the sky- that is, lies on a plane containing the Earth, will show up as a sine-like curve on a wide field image mapped to a plane. The only exception is for objects that lie on the plane defining an inclination of zero in the data coordinates. Those objects will describe a simple line on the projection.
Imagine that you hold a hula hoop flat (inclination 0°) at eye level, and turn around inside it. Clearly it describes a line through the middle of your visual field. Now tip it (say, inclination 45°). Clearly, it will be low in your visual field when you are turned in one direction, high opposite that, and crossing diagonally through your field in between those two positions. If you were to plot the vertical position of the hoop at each angle of rotation, you'd get a sine curve.
On a very wide field astronomical image, the horizontal axis is usually the angle as the camera has rotated, and the vertical axis is the angle away from the plane of rotation.