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This technique can be used to observe the rotation curve of a galaxy, as those stars moving towards the observer are blue-shifted, while stars moving away are red-shifted. [2] Long-slit spectroscopy can also be used to observe the expansion of optically-thin nebulae. When the spectrographic slit extends over the diameter of a nebula, the lines ...
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While from an infalling observer's perspective the plunge into a rotating black hole occurs in a finite proper time and with very high rapidity (left), from the perspective of a coordinate observer at infinity they slow down, approaching zero velocity at the horizon relative to a stationary probe on site while being whirled around forever by ...
Bouncing ball in a rotating space station: The objective reality of the ball bouncing off the outer hull is confirmed both by a rotating and by a non-rotating observer, hence the rotation of the space station is an "absolute", objective fact regardless of the chosen frame of reference.
An observer standing on Earth's equator visualizes the celestial equator as a semicircle passing through the zenith, the point directly overhead. As the observer moves north (or south), the celestial equator tilts towards the opposite horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus ...
where the angular rotation of the frame is expressed by the vector Ω pointing in the direction of the axis of rotation, and with magnitude equal to the angular rate of rotation Ω, symbol × denotes the vector cross product, vector x B locates the body and vector v B is the velocity of the body according to a rotating observer (different from ...
The equatorial plane is the plane perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°. The convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits (backward). Thus:
At this rotation rate, mass can be readily lost from the equator, forming a circumstellar disc. See also break-up velocity. [7] culmination. Also meridian transit. The apparent movement of an astronomical object (e.g. the Sun, the Moon, a planet, a star, a constellation, etc.) across the observer's local meridian.