Questions tagged [coordinate]

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

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1 vote
0 answers
93 views

Deriving orbital inclination from equatorial coordinates?

I wanted to ask if it's possible to establish a correlation between the observed equatorial coordinates of a Solar System planet, especially declination, and the planet's orbital inclination with ...
4 votes
1 answer
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Transformation of hour angle to azimuth

Converting Hour angle to Azimuth, is there a simple way to know which result is correct (as the formulas and the arccosine give various results shifted by 180° etc.), or does one just have to figure ...
2 votes
0 answers
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From TEME to RA DEC

I am using the SGP4 python package to get the coordinates of satellites at a given epoch. The algorithm computes the positions (X, Y, Z) in the True Equator Mean Equinox coordinate frame (TEME). From ...
2 votes
0 answers
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Figuring out camera pitch and roll given RA and DEC of center of image, as well as lat,long of camera and time taken

What I am trying to figure out is how to get the camera pitch and roll, as described in this image (the green yaw line is where the camera sensor is pointing if given a RA, DEC (of center of image,ie ...
2 votes
0 answers
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How to use astropy to join data tables based on sky coordinates?

I have 2 astronomical tables, from a fits file and a csv file, that look something like this ...
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1 answer
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Mismatch between the equation of the equinoxes and the correction for a right ascension

I am studying about apparent and mean positions of Sun using quite old books: Astronomical algorithms (1991) and Explanatory supplement to the astronomical almanac (1992). The question is about the ...
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4 votes
2 answers
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Are the Vernal Point and the Autumnal Point two antipodal points on the celestial sphere?

Intersections of the elliptic and the equatorial planes on the celestial sphere are the Vernal Point and the Autumnal Point. Are these two points two antipodes on the celestial sphere of the Earth?
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1 vote
2 answers
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Is the Vernal Point a fixed point on the sky?

The Vernal Point is a reference point in the Equatorial Coordinate System, from which R.A. is measured. My book says that the zero point of Right Ascension, i.e. the Vernal Point keeps moving in the ...
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1 vote
0 answers
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Derivation: Formula for projection of sun's motion onto parallel of declination

Consider the projected angular velocity of the sun along a parallel of declination. I was told that it is $$\frac{\cos\varepsilon}{\cos\delta_{\odot}} \frac{d\ell_{\odot}}{dt} \tag{1}$$ where we let $\...
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1 answer
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How to determine errors in coordinates from SIMBAD error ellipse

How to determine errors in ICRS coordinates from the SIMBAD error ellipse, please? Thank you
3 votes
1 answer
438 views

Right ascension - Gaia vs Simbad

What is the difference between Right ascension in Simbad and Gaia Archive, please? How to convert the values? For instance, HD 37468: 05h 38m 42.0s vs 84.68652242854718 deg. Should not be these values ...
4 votes
1 answer
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Problem in converting equatoral coordinates to ecliptic coordinates

I would like to convert equatoral coordinates to ecliptique coordinates. I am following the source below: Practical Astronomy with Your Calculator The formula I am using is: When I solve this example,...
0 votes
2 answers
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Which mobile/computer application can help me understand celestial coordinate systems better? [closed]

I wish to understand Equatorial and Altazimuth coordinate systems much better. Any applications or softwares which can help me out with the same?
4 votes
2 answers
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Measurement unit of coordinate systems in astronomy

Nearly all of the coordinate system I have studied in Positional astronomy use the degree system. This makes me curious about why astronomers prefer degrees over radians as we know that Radian is a ...
1 vote
1 answer
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Astrometry and Geometric Distortions

CCD's are widely used for astrometry. Since a spherical surface (the celestial sphere) is projected onto a rectangular surface, the plate scale or pixel scale (approximated with 1/focal length etc) is ...
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Calculating the angular momentum of stars from Gaia archive (Gaia DR3)

I am trying to calculate the angular momentum for a subset of stars from Gaia DR3. I have scanned the available fields in their database and could only find out the below fields that specifies the ...
1 vote
1 answer
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How are the lines from objects onto the ecliptic called?

See this screenshot from SpaceEngine: Many other examples from websites etc. Do they have a name? I couldn't find anything. If I'm not mistaken, those should be the z-coordinate of galactic ...
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1 vote
1 answer
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Using setting circles on a German Equatorial mount

Recently I have been working on equatorial grid system consisting of the right ascension and declination coordinates. Even after understanding the concept behind those coordinates, I am puzzled by the ...
1 vote
1 answer
116 views

How to get coordinates and brightness of all stars from 1 constellation on SIMBAD?

I would like to get the RA and DEC coordinates and brightness data of all stars in the Orion constellation from SIMBAD. I am attempting to do a 'criteria query' but I'm confused about how to sort the ...
2 votes
0 answers
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Why are the sky distributions of SDSS DR16 and DR16Q different?

I've downloaded the csv files for SDSS DR16 and DR16Q and made a map of their sky distributions: The coordinates come from: DR16: RA_ICRS and ...
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1 answer
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How does a black hole look like independently of coordinates?

Observing a black hole from far away, far it looks as if infalling matter accumulates on the horizon. If one falls in though, there is no horizon at all (or it always stays in front of you). Which ...
3 votes
1 answer
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How can you derive equations between the Horizontal and Equatorial system if the two systems have different centers?

This might be a dumb question. If the center of the celestial sphere is the center of the earth, and the center of the horizontal system is the observer, why do people use this diagram to derive ...
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2 votes
1 answer
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Celestial coordinates of every pixel in the image

I am solving starfield using Astrometry.net, an amazing piece of software I must say. After solving the starfield, Astrometry gives celestial coordinates of centroids of every star in the image, as ...
1 vote
0 answers
119 views

Plotting galaxies in 3-D

Suppose I have a catalogue of galaxies in a .dat file with each row representing information about a galaxy: right ascension of the galaxy, declination of the ...
1 vote
1 answer
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Celestial Coordinates and Sun's degrees below horizon

I am struggling to understand the how the coordinates work. Example: At vernal equinox RA=0 DEC=0, Does this mean the Sun is at its highest point at the equator? If my mean solar time is 2h 30min, ...
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1 vote
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Angle to the line of sight

I don't understand this angle used in galaxy clustering. There is the line of sight and this angle to the line of sight which is not clear to me. Here is a transcript of a description from 1705.05442: ...
2 votes
2 answers
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Measure the deprojected distance between two points?

I have an image of a protoplanetary disk, from which I would like to measure the distance of various points from the centre. See below image for an example, where I would like to measure the distance ...
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2 votes
0 answers
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Azimuth and Altitude angle between two points in the sky

I want to know how to correctly calculate altitude and azimuth difference, separately, between two points in the sky. The same way will be with icrs coordinates. For the altitude difference, I simply ...
5 votes
0 answers
118 views

Airy's Water Filled Telescope: help required to fully understand the calibration procedure followed

I am reading/studying the instrument description of Airy's Water Filled Telescope (Airy, G. B., "History and Description of the Water Telescope of the Royal Observatory, Greenwich", ...
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2 votes
0 answers
148 views

What is the relationship between true anomaly and solar longitude?

So, my ultimate objective is to map solar longitude values onto a pseudo-Gregorian calendar. I thought this would be simple, but it has turned out to be anything but. I have asked several questions on ...
6 votes
1 answer
104 views

Doubt about a computation in Jules Verne

In his Aventures de trois Russes et de trois Anglais dans l'Afrique australe (The Adventures of Three Englishmen and Three Russians in South Africa), Jules Verne describes in some detail the geodetic ...
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1 vote
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Convert Earth-centered coordinates to rotating libration point (RLP) coordinates?

I'd like to plot the path of an object near L2 (like the Webb space telescope) in a rotating libration point coordinate system. That makes it is easy to distinguish halo orbits from more general ...
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3 votes
1 answer
191 views

What's the Right Ascension & Declination of Galactic Left & Galactic Right?

For the purpose of being able to align my model to the galactic plane, I want to know the directions of the galactic center, anti-center, north, south, left & right. This gives me the answer for ...
6 votes
2 answers
367 views

What is the maximum latitude from which a satellite in a geostationary orbit around Saturn would be visible to an observer on the planet?

This question is part astronomy and part mathematics. I'm aware it involves “basic” trigonometry, but my brain is short-circuiting. From my calculations, the distance from the center of Saturn where a ...
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2 votes
2 answers
365 views

Horizontal and equatorial coordinate systems

What is the difference between horizontal and equatorial coordinate systems apart from the notations (azimuth, altitude) and (right ascension and declination angle)? Please provide some measurements ...
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1 vote
1 answer
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TESS sector of observations in RA/DEC vs lat/long

I'm trying to figure out WCS & just generic astronomical coordinates system, in order to better understand/use TESS data. I've been reading the mit docs, but I can't understand the reasons for ...
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2 votes
1 answer
750 views

What is the connection between declination and latitude?

The celestial equator is a projection of the terrestrial equator on the celestial sphere. So doesn't that mean the geographical latitude and the declination will be "exactly" equal, as they ...
2 votes
1 answer
79 views

What is a "valid" coordinate system?

I was reading "Natural Coordinate System in Curved Spacetime" by Ying-Qui Gu. The first sentence of the abstract struck me (bold emphasis added by me): In this paper we establish a ...
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1 vote
0 answers
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Converting a Satellite's position in Lat/Lon/Alt/Time to RA/Dec

I'm trying to convert a satellite's position given in latitude/longitude decimal degrees, altitude in meters, and time in milliseconds since epoch to right ascension and the declination. I have found ...
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21 votes
4 answers
5k views

Where is it possible to observe the Moon for 24 hours?

I wrote an astronomy olympiad yesterday and there was one task I couldn't figure out an answer to: Estimate at what latitudes it is possible to observe the Moon for at least 24 hours. Under what ...
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4 votes
2 answers
254 views

Mathematics for Conversion between ICRS and AltAz

I am writing some software, for my own learning experience, to convert astronomical coordinates to different frames of reference. An example of this would be conversion between ICRS which a lot of ...
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1 vote
1 answer
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At what time of the day of autumnal equinox the Sun's equatorial coordinates reach max value?

I'm trying to solve this task: At what point in time of autumnal equinox day, at sunrise or sunset will a) the declination of the Sun b) the right ascension of the Sun reach the maximum value? I'm ...
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1 vote
1 answer
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Altitude of Polaris is latitude

How to prove geometrically that the altitude of Polaris is equal to the latitude? I have seen in handouts that the altitude of the pole star gives the latitude of that place.
1 vote
0 answers
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What is the Sun's absolute direction called?

Like the Sun's direction relative to the local standard of rest is called "solar apex" What term can I google instead to find info about the Sun's direction relative to the CBBR? I ...
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0 votes
2 answers
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Given a location and a time on another planet, how do you determine how many hours before or after sunrise is it there?

I'm actually not so much interested in sunrise/sunset times. What I want to know is how to relate local planetary coordinates (e.g., planetary lat/lon) to, for example, heliocentric coordinates at a ...
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3 votes
2 answers
154 views

How come I can point to two places with telescope and have the same coordinates?

Absolute beginner here. I read through the telescope manual, watched many videos, and got a pretty decent understanding of DEC and R.A. However, I don't understand one thing (where theory doesn't ...
1 vote
0 answers
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How does the rock Simurgh Saxum (-25.32°, 4.05°) on 101955 Bennu define its prime meridian and serve as the basis for its coordinate system?

Spaceref's NASA's "Tour of Asteroid Bennu" Selected for Prestigious Computer Graphics Film Festival says: It's hard to imagine what the surface of asteroid Bennu might look like - it's ...
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1 vote
1 answer
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Understanding the constant 6.697374558 when finding GMST

I'm trying to understand the constant 6.697374558 mentioned in this question: The Astronomical Almanac gives an expression for approximate mean sidereal time, in hours: $$\mathit{GMST}=6.697374558+0....
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6 votes
1 answer
549 views

Conventional units for astronomical object coordinates

I would like to know what the conventional units for identifying a celestial object (J2000.0) are. For instance, I am reading a paper in which they refer to object SDSSJ170013.70+400855.6; I am ...
1 vote
1 answer
108 views

What are the aspects does the moon differs between cities located on the same latitude?

What are the aspects does the moon (astronomical position and other astronomical aspects) differs between cities located in the same latitude? - For example: Seattle, Munich, Vienna, and Ulaanbaator ...
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