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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21
votes
3answers
9k views

Could someone explain RA/dec in simple terms?

The equatorial coordinate system isn't too complicated. However, for people new to this, it seems rather intimidating at first. Is there an easy way to explain it?
12
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1answer
966 views

Do stars of a galaxy change their positions relatively to each other?

Complete astronomy noob over here who would be happy if he get a simple answer (and who is also aware that this may be not possible)... I've learned from a tv documentary that the stars at the edge ...
10
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1answer
7k views

Local Sidereal Time

I am trying to understand how to calculate local sidereal time and have found the following formula: $$\text{LST} = 100.46 + 0.985647 \cdot d + \text{long} + 15 \cdot \text{UT}$$ Here, $d$ is the ...
10
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1answer
2k views

Given a date obtain latitude and longitude where is the sun zenith

Searching is easy to find terminator line (frontier between day and night) or the position of the sun in the sky given a position on the earth and a time; but I can't find how to obtain where is the ...
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3answers
2k views

Coordinate system for space [closed]

I am high school student, I have doubt if I have to locate a planet or any star in space, how do I locate it, because we have no perfect coordinate system, I have read in some books, that time is ...
8
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3answers
1k views

Determining latitude and longitude in bad weather

In Sobel's famous book 'Longitude', she described the story of Harrison. I still have one question. What if it is cloudy on the sea? In this case, the sailors have nothing to compare with, right? This ...
8
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3answers
5k views

How do I plot galactic coordinates using matplotlib and astropy in python?

I want to make a projection of millisecond pulsars on the galactic plane, much like this one from Sala et al. 2004: I have tried several methods, and have not gotten anywhere. This is my current ...
8
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1answer
3k views

Calculate latitude and longitude based on date and sun

I can't seem to find this algorithm, if it exists. Can you calculate the longitude and latitude of where you are standing based on the date and the angle of the sun? Also, would the algorithm work for ...
8
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2answers
344 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. ...
7
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2answers
282 views

Different times of sunset at the same location due to elevation

Me and my friend were watching the sunset on the same location (at my country the latitude is approximately 40 degrees). I am at sea level and my friend is at an elevation. He observed the sunset with ...
7
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1answer
583 views

Calculation of Horizontal Coordinates

Given a fixed coordinate location on Earth (i.e. a latitude and longitude), and a fixed equatorial coordinate location of a particular astronomical object in the sky (i.e. right ascension and ...
6
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4answers
3k views

Need Simple equation for Rise, Transit, and Set time

I've been looking, unsuccessfully, for hours for a simple set of equations: Input: RA and Dec of an object Observers Lat and Lng Current Time Output: Rise Time Transit Time Set Time (and, ...
6
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1answer
221 views

How was the galactic plane established?

As pointed out in this answer the axes of galactic coordinates are defined such that galactic longitude and latitude (0, 0) point toward the galactic center. But then the plane defined by galactic ...
6
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1answer
1k views

Why is the symbol of Vernal Equinox ♈?

Since the direction of Vernal Equinox lies in the Pisces constellation, why is its symbol Aries? Shouldn't it be ♓ ? Is this a historical anachronism, only invalidated by axial precession of Earth?
6
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1answer
520 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 ...
6
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1answer
2k views

Calculating RA/dec from JPL ephemeris data

I'm using JPL planetary ephemerides to calculate the position of planets. Using DE405 ephemeris (using a parser provided by Project Pluto with all tests passing). I am fetching the position of Mars ...
6
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2answers
2k views

Why is right ascension measured in hours?

When viewing star maps in Stellarium, I noticed that the meridians of the equatorial grid were denoted in hours and not degrees, and that always puzzled me. Why did astronomers choose this system? I ...
6
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1answer
3k views

Convert coordinates between RA/dec and WGS 84 (SRID=4326)

I've imported the HYG Database from http://www.astronexus.com/node/34 and now I need to convert all RA/dec stars positions to fit in a WGS 84 coordinates (SRID=4326) PostGIS map (-180 to 180, 90 to -...
5
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1answer
499 views

Coordinates in the Night Sky

I've learned about Orbits recently, and there are 6 orbital elements. Now, I've heard of three coordinate systems whereas, they can help you measure positions of stars in the night sky. The Altazimuth,...
5
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2answers
589 views

Where is the North of the Universe

Does it exist North of the Universe? (Which is probably used for determining coordinates of far galaxies.) If so, then where it is? On what is it aligned? (Is it orientated on Earth, Sun, Milky Way, ...
5
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2answers
313 views

Data to "check" Kepler’s first law

I want to "check" Kepler’s first law by using real data of Mars. From the equation of the ellipse, I derived $$\frac{1}{r}=\frac{a}{b^2}+\frac{a}{b^2}\cdot\epsilon\cdot\cos(\varphi),$$ where ...
5
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1answer
2k views

How to convert density from physical unit to comoving unit?

I am learning co-moving units and I am interested to see how the conversion works. If Hubble constant is assumed to be 0.7, then I want to convert $1gm/cm^3$ into comoving unit. If I want to express ...
5
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2answers
2k views

Software to convert RA and DEC into ALT and AZ

I have implemented the formulas to convert AR and Dec into altitude and Azimuth in C++ following the book Practical Astronomy with your Calculator or Spreadsheet 4th Edition. In the book there is an ...
5
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1answer
336 views

Coordinate transformations between reference frames in spherical astronomy

Suppose there are two observational frames of reference with origins $O$ and $O'$, respectively, separated by some constant distance. A body located at point $P$ has Cartesian coordinates $\left(x,y,z\...
5
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1answer
1k views

Conversion between Astronomical Frames, ex. IRCF, FK5, FK4, etc…

I'm a little bit confused about reference frames, and I was wondering if someone could help clarify a few things? So let's say I have equatorial coordinates that refer to the mean equator and equinox ...
5
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2answers
463 views

How do I find the RA of sunset and sunrise in a specific location?

I want to make some observations with a telescope in Hawaii on Mauna Kea but I am living somewhere else (not Hawaii) and I want to plan a night's viewing on the Hawaiian telescope. How do I find the ...
4
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4answers
839 views

Latitude, longitude and altitude of Ckoirama Observatory; where can things like this be looked-up?

This answer to Is Starlink 1130 (Darksat) really dimmer? links to the March 16, 2020 paper in arXiv First observations and magnitude measurement of SpaceX's Darksat which finds only a modest decrease ...
4
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3answers
491 views

Measuring misalignment between two positions on sky

Let's say I have the (RA,Dec) for two positions on the sky. I want to measure the position angle between these two positions. In other words, if I had the Cartesian coordinate vectors for these two ...
4
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3answers
1k views

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

From several texts I have read, I have learned that right ascension is measured on a scale of 24 hours. I understand that Earth rotates almost exactly 360 degrees relative to distant objects, which is ...
4
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1answer
3k views

Is there a map of the galaxies?

I see that there are many maps of a single galaxy, the Milky Way, showing the positions of the stars within our galaxy. I could not find a map of Galaxies, however. Is there such a map? In lieu of ...
4
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1answer
947 views

Why do J2000 coordinates change with time in Stellarium?

I'm new to the field so I'm sure this is a basic misunderstanding. As I currently understand it, J2000 equatorial coordinates describe the position of objects by referencing a specific point in time (...
4
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1answer
126 views

Astronomical Term *Mezzocielo*

What is the name of the point of intersection of the great circle passing through the celestial north pole P and the Zenith Z, with the celestial equator? (Point T in the figure) In Italian this point ...
4
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2answers
213 views

What kind of a visual trajectory would an asteroid have if it were to hit Earth?

Let's say that Peter has a set of superb telescopes and he's watching the sky every night, for 3-4 months. He may not know it just yet, but there is an asteroid heading towards Earth, on a crash ...
4
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1answer
764 views

Which is the shape of the sky?

I'm a software developer and I'm developing a planetarium and the first thing that I don't know is: What is the shape of the sky? First, I though that it is a semi-sphere, but searching on Internet I ...
4
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1answer
138 views

Is the longitude assigned to sunspots spherical or projected?

Sunspot maps are created from a projection of the sun, so the coordinates of sunspots (or active regions in general) are assigned according to it. Do these coordinates correspond to actual spherical ...
4
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1answer
1k views

How to get the axial tilt vector(x,y,z) relative to ecliptic

According to the orbital plane XYZ, I understand that the axial tilt is the angle between the planet axis rotation and any normal of the plane (actually Z in right handed system). BUT, this is not ...
4
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2answers
1k views

Why objects are uniquely defined by their right ascention and declination?

I've just started studiyng Astronomy. I understood how I would measure Right Ascention and Declination: for the first one I'd trace an Hour cirlce to the Celestial Equator, and then, compute the ...
4
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1answer
198 views

Usefulness of the hour angle (HA)

The Hour Angle (HA) is measured west from the observer's meridian in hours, mins, seconds. How is the Hour Angle used to help plan observations during the night at a telescope?
4
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1answer
124 views

How can the IAU 2000A vs IAU 2000B nutation comparison be reproduced?

I am attempting to plot how the IAU 2000A nutation model degrades as its terms are omitted. As a spot-check, I decided to compare it to IAU 2000B, which includes only the 77 most important lunisolar ...
4
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1answer
6k views

What part of the milky way do we see from earth?

When looking up at the night sky, we can sometimes observe a bright band of stars stretching across it. I know this is our galaxy but exactly what are we looking at? Could we look at the centre of ...
4
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1answer
90 views

Information about known objects in the Universe

I want to retrieve coordinates, photos, and information (size, atmosphere composition, distance from Earth, etc.) about every known object in the universe. Ideally, the information is available via an ...
4
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1answer
73 views

Protocol for establishing longitudinal meridians on other heavenly bodies

When we first observe a new heavenly body (it could be a new star, asteroid, etc.,or a minor planet in our own solar system), are there any procedures set in place for establishing a system of ...
4
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1answer
884 views

Calculate telescope orientation based on RA, DEC and Lat/Long

I'm parsing FITS files for a project based on data from a telescope. These files include 'DEC', 'RA' and lat long values. I understand roughly the concept of celestial coordinates and I assume that ...
4
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0answers
131 views

Time evolution data of the Great Red Spot on Jupiter?

Jupiter's Great Red Spot fascinates scientists for ages, so it does me. Where can I find a table (e.g. as CSV-file) with the time evolution of longitude, latitude, horizontal and vertical extension of ...
3
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2answers
1k views

Difference between J2000, FK5 and ICRS coordinate systems? Which one does the Yale Bright Star Catalog use?

I have no background in astronomy. I have been wanting to write code to make star charts for a given location and time, which led to this question. I figured out that I would need to convert the ...
3
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2answers
117 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 ...
3
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2answers
67 views

When (yyyy-mm-dd) does the north pole of uranus most nearly point towards the sun?

When (yyyy-mm-dd) does the north pole of uranus most nearly point towards the sun? The information I've found suggests this happened in 1944 or 1945, but would like to find a more precise date or ...
3
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1answer
117 views

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

first post here. I found 1 related Question, which has not solved my Problem. SHORT QUESTIONs VERSION: Suns axis is 7,25° tilted from the ecliptic. But in which direction? LONG QUESTION: Nasa ...
3
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1answer
141 views

Is this how stars’ right ascensions correlate to planets’ longitudes on a 2d map?

This is my first ever online question, so please bear with me: I’m working on an A1-sized map of at least 100 of the largest solar system bodies (henceforth just called ‘planets’, ignorning the IAU ...
3
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1answer
352 views

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

I'm looking up how to convert an azimuth/elevation measurement from a specific location on Earth's surface to right ascension/declination. I'm coming across the terms "topocentric declination" and "...

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