ORIENTATION OF THE ORBIT - on the size of the orbit the...

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ORIENTATION OF THE ORBIT In the figure above the straight line path of the star (the y-axis) is perpendicular to the paper. The star is going "into" the paper. It's wobbly motion might be left and right, toward and away from the observer (along the x-axis), and so it would be detected via the Doppler effect. Or, its motion might be up and down (the z-axis), and this up- down motion would be seen directly on the telescope's photo. This figure also shows that the wobbly motion doesn't have to be along the x-axis or the z-axis, but could be on an angle as shown by the doubled line with arrows. In fact, most of the orbital motion we detect is probably like this. In this case we would detect wobbly motion with either the astrometric method or the Doppler method. It also shows that if we use one of these methods, we are probably detecting only part of the actual motion. If I observe the wobble with the astrometric method I am probably finding just a lower bound
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Unformatted text preview: on the size of the orbit; the orbit could be bigger than what I detect. Similarly, if I observe with just the Doppler method I am also finding just a lower bound on the size of the orbit. This means when I use these methods to find the mass of the invisible companion, I am really finding a lower bound. The mass could be what I calculate, or it could be larger. Both the wobble methods (astrometry and Doppler) are easier to observe if the mass of the invisible companion is larger. Hence they are, you might say, prejudiced against smaller masses. If we don't see many smaller masses it's not so much that they are not there, but that our system of detection doesn't find them as easily. The wobble methods are also prejudiced in favor of planets that are close to their stars, since the gravitational force, which produces the wobble, is greater if the planet is closer. The gravitational lensing method (below) however, works the other way....
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