Questions involving basic astronomical concepts or information.

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Calculate time when star is above altitude 30°

To find the best observation time for an object, I'd like to calculate the time when it is 30° or more above the horizon. Local Sideral Time would be sufficient. To include that in my program, I need ...
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1answer
27 views

Can angular information be known more precisely than the diffraction limit?

The diffraction limit deals with the ability to determine if two things are separate. I am interested in the ability to find the the centroid of a single object. Imagine a star with no near ...
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1answer
43 views

What exactly is 'eastward movement'

I am reading a book on spherical astronomy. Surprisingly, my problem is not with the mathematics. The author mentions several times words like 'eastward movement' and 'westward movement'. For example, ...
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1answer
32 views

Determining distance from semi-major axis and eccentricity

I am trying to obtain the distance covered by an object in orbit around the earth within a specified amount of time past its perigee passage. The object is in an elliptical orbit with eccentricity 0.2 ...
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0answers
44 views

Planetary reference systems and time

I am researching into how coordinate systems of solar systems objects are created by reading some of the reports written by the Working Group on Cartographic Coordinates and Rotational Elements (e.g. ...
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0answers
36 views

Coordinates of the Moon

How does one compute the right ascension and declination of the Moon at a given time (or for that matter, the altitude and azimuth)?
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33 views

What is the shape of the Sun's orbit around the Earth taking into account elliptical orbits?

Consider the non-inertial frame that is at rest with respect to the Earth's revolution around the Sun. (Ignore the Earth's rotation around its own axis.) My question is, what is the shape of the ...
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59 views

How are errors on X-ray photon index propagated to X-ray spectral index?

I have seen that in X-ray astronomy, astronomers often talk in terms of photon index $\Gamma$, which is related to spectral index $\alpha$ by relation $\Gamma$ = $\alpha$ + 1. Are the errors on ...