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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20
votes
3answers
8k 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?
9
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1answer
797 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 ...
9
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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 ...
8
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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
votes
1answer
4k 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 ...
8
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1answer
2k 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
votes
2answers
271 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
votes
1answer
463 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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1answer
159 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
776 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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3answers
2k 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
votes
3answers
802 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 ...
5
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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 ...
5
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1answer
1k 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 ...
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
votes
1answer
2k 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
votes
1answer
237 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
votes
1answer
951 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
votes
2answers
257 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
votes
3answers
233 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
votes
2answers
344 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, ...
4
votes
3answers
722 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
votes
1answer
2k 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
votes
1answer
897 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 ...
4
votes
1answer
400 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
votes
1answer
115 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
votes
1answer
682 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
votes
2answers
183 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
votes
1answer
67 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
votes
1answer
5k 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 ...
3
votes
1answer
84 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
votes
1answer
94 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 (...
3
votes
2answers
201 views

What are the RAs of the boundaries between traditional zodiacal signs?

I'm trying to figure out at what right ascension (RA) — not celestial longitude — the sun enters the various traditional (Western) astrological signs of the Zodiac; but I can't figure out how to ...
3
votes
2answers
398 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 ...
3
votes
1answer
1k views

How to project galaxy data in x y z coordinates?

For a data visualization project, I want to extract galaxy data (in x y z coordinates) from galaxy catalogue of within 150 mpc and project each of those galaxies as dots and visualize them in a 2D ...
3
votes
3answers
311 views

Differences between alt/az in Stellarium and Astropy

I've just started to learn Astropy. It's a nifty tool. Using some tutorials, I wrote and then made modifications to a little script that finds the Alt/Az of an object at a certain place and time. I ...
3
votes
1answer
256 views

360 degree equirectangular projection of all naked eye stars with precessional motion for simulating

For many years now I've been using Voyager sky simulator by Carinasoft. The projection selections are great, but Equirectangular doesn't seem to one one of them. Is there a program out there that does ...
3
votes
2answers
299 views

Stellar Mapping and Coordinates [closed]

Why are the Galactic Coordinates not aligned so that the Axes go through the Long Bar Y-axis aligned to it's longer side, positive with Sol, and the X-axis align to the center of the short length with ...
3
votes
1answer
298 views

Math for calculating the terrestrial longitude directly under the sun with time

I'm trying to calculate the longitude on the earth where it's noon at some time. (That is, the longitude which is coplanar with the plane defined by the sun and the earth's axis.) Here is my python ...
3
votes
1answer
153 views

What is the abbreviation for solar time, hour angle of the sun?

I understand that the hour angle and declination can be abbreviated as (HA Decl), and rectascension and declination as (RA Decl). The hour angle of a star is of course zero hours at the meridian. The ...
3
votes
1answer
737 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 ...
3
votes
0answers
473 views

Earth-Centered Earth-Fixed coordinates with respect to heliocentric coordinate system at vernal equinox

I am trying to calculate the position of a point on the Earth's surface with respect to the Sun's center at a certain date and time. For what I am trying to do it is OK to ignore precession of Earth's ...
3
votes
0answers
78 views

Is Nomad data heliocentric or geocentric?

I'm wondering if the data in star catalogues are heliocentric equatorial coordinates or geocentric equatorial coordinates. Also given the distance between stars compared to the distance between the ...
2
votes
2answers
125 views

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

As the orientation of the moon is different in the northern and the southern hemisphere, is the orientation of the sun different in both hemisphere? Does a sunspot appearing in the Sun northern ...
2
votes
2answers
175 views

Does anybody know how to get Sun-Jupiter Lagrangian points L4 and L5 RA and Dec?

I wanted to point at the L4 and L5 of Sun-Jupiter to find Trojan asteroids but I don't know how to calculate the RA and Dec of these. Do you know of any software that does it for you or how to ...
2
votes
1answer
119 views

a random distribution of RA&Dec

How to make random positions in Equatorial coordinate system? If I divide Dec between -90 and 90 evenly, the space distribution is not random.
2
votes
2answers
364 views

What zodiac constellation will the Vernal Equinox be directed towards in ~6500?

My question is basically asking how the vernal equinox changes with time, and how we can track where it will be at certain points in time.
2
votes
1answer
56 views

When is the best time to observe M81 from the Northern Hemisphere?

I have read that the best time to view M81 is during the spring. Considering its RA is ~10h and Dec. is +69°, wouldn't February 21st be the best time to view it since this is about when it transits my ...
2
votes
1answer
184 views

Is this a black hole?

While researching about galaxies in Google sky, I came upon a strange area. Co-ordinates: 11h 6m 15.0 seconds | -77° 22' 9.8" A lot of space around this body is empty, is there a possibility that ...
2
votes
1answer
154 views

What's the difference between GSR and Grf

I note there are two terms about Galactic rest frame in literatures: Galactic Standard of Rest (GSR) and Galactic Rest Frame (Grf). Are they the same frame? If not, what's the difference?