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Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation.
These distortions will move across spectral line profiles due to the stellar rotation. The technique to reconstruct these structures on the stellar surface is called Doppler-imaging, often based on the maximum entropy image reconstruction to find the stellar image. This technique gives the smoothest and simplest image that is consistent with ...
In astrophysics, Zeeman–Doppler imaging is a tomographic technique dedicated to the cartography of stellar magnetic fields, as well as surface brightness or spots and temperature distributions. This method makes use of the ability of magnetic fields to polarize the light emitted (or absorbed) in spectral lines formed in the stellar atmosphere ...
Attempts to model of galaxy rotation based on a general relativity metric, showing that the rotation curves for the Milky Way, NGC 3031, NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter [44] and other similar work [45] have been disputed. [46]
Diurnal aberration: "The component of stellar aberration resulting from the observer's diurnal motion about the center of the Earth due to the Earth's rotation." Secular aberration: "The component of stellar aberration resulting from the essentially uniform and almost rectilinear motion of the entire solar system in space. Secular aberration is ...
Exposure times must be short (under a minute) to avoid having the stars point image become an elongated line due to the Earth's rotation. Camera lens focal lengths are usually short, as longer lenses will show image trailing in a matter of seconds. A rule of thumb called the 500 rule states that, to keep stars point-like,
The slightly longer stellar period is measured as the Earth rotation angle (ERA), formerly the stellar angle. [4] An increase of 360° in the ERA is a full rotation of the Earth. A sidereal day on Earth is approximately 86164.0905 seconds (23 h 56 min 4.0905 s or 23.9344696 h).
The following is a list of stars with resolved images, that is, stars whose images have been resolved beyond a point source. Aside from the Sun , observed from Earth , stars are exceedingly small in apparent size, requiring the use of special high-resolution equipment and techniques to image.