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Questions on systems to uniquely determine position of a point or other geometric element on a manifold such as Euclidean space.

1 vote

How to deal with the celestial meridian?

I think you are overlooking these factors: Iowa State University is at 42 degrees North latitude, so the Sun and celestial equator that they are showing in their figures are always to the south at t …
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1 vote

Specific word for the point of the terrestrial surface "under" a star or other object in the...

Positions are usually given relative to the observer, not relative to the object. So instead of saying "I am under the star X", you would say "star X is overhead". The word for an object directly over …
JohnHoltz's user avatar
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2 votes

Geo Helio and RA

The heliocentric coordinates then get converted to other coordinate systems. … Geo longitude (Lng) is the ecliptic longitude as seen from the Earth (Geo), but otherwise, the coordinate system is the same. …
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4 votes
Accepted

Celestial Coordinates

The coordinate system for an object in the sky measured relative to the horizon is known as altitude-azimuth. … See Horizontal Coordinate System on Wikipedia …
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2 votes

Clarification on Greenwich Sidereal Time (GST)

The flaw in your logic is that "RA and L are constants". The right ascension (RA) of the object on the meridian is not constant. It changes continuously, otherwise we would not say that the sky is ris …
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6 votes
Accepted

Is the sun flipped on the other side of the world?

Yes, the orientation of the Sun will be different from the Earth's northern and southern hemisphere, just like your example of the Moon. I would not say that a sunspot in the "northern" hemisphere wo …
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3 votes
Accepted

What is the connection between declination and latitude?

It may be easier to visualize the formula by calculating the altitude based on the observer's latitude (lat) and the object's declination ($\delta$), and then re-arranging the equation to find the obs …
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3 votes

Why is right ascension measured on a 24 hour scale rather than a 23 hours and 56 minutes scale?

The problem is not that right ascension goes from 0 to 24 hours (or 0 to any other number). The problem is that the Earth is revolving around the Sun, and our time system is based on the Sun. Because …
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5 votes

What does it mean that the Sun`s rotation axis is: RA 286.13° , Dekl: 63.87°?

You can think of the position given in your title as the coordinates of the star that is directly over the Sun's north pole. (Similar to how Polaris is almost directly over the Earth's north pole.) Li …
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4 votes
Accepted

What is meant by *topocentric* right ascension and declination?

You are correct that topocentric coordinates are for the position of "close" objects, corrected for observing from the Earth's surface instead of the theoretical center. The topocentric and geocentri …
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4 votes

Measuring misalignment between two positions on sky

The position angle P of a body ($\alpha_1, \delta_1$) with respect to another body ($\alpha_2, \delta_2$) can be calculated from $$tan(P)={sin(\Delta\alpha)\over cos(\delta_2)tan(\delta_1)-sin(\delta_ …
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4 votes
Accepted

How to calculate the ground track of the Moon's position on the Earth's surface?

Given a date and time, the position of the Moon can be calculated to provide the declination and right ascension. The sub-point of the Moon (the point on the Earth at which the Moon is at the zenith) …
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