# Questions tagged [positional-astronomy]

Questions about positions of objects in the sky, either relative to a fixed coordinate system like the equatorial and ecliptic coordinate systems, or relative to an observer's point of view.

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### What are the Mathematical Algorithms/Formulas behind hindu Sunrise and Sunset Calculations?

There are differences between Astronomical Sunrise/Sunset calculation and Hindu calendar Sunrise/Sunset calculations. The astronomical algorithms to calculate the sunrise/sunset can be found over the ...
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### Where can I get J2000 epoch initial mean longitudes for all planets and celestial bodies?

I'm following this paper to calculate geocentric coordinates. The authors have provided the initial mean longitude values for the planets (provided in attached table) for 01.01.2000 @ 00.00 UT but I'...
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### Converting rectangular to polar coordinates

I'm following the steps in this paper on how to calculate geocentric longitude. In section 3.4.2 it says the Geocentric rectangular co-ordinates of Mercury then are: ...
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### Map planetary eccentricity on a perfect circle? [closed]

What is the formula to plot an eccentric orbit on a perfect circle? I have estimated the full degrees each planet would occupy on a 360 degree wheel (natal chart) but how do I take into account a ...
218 views

### Understanding the JPL Ephemerides

I'm working on an animation that replicates our Solar System. I know this has been done before, but I'm working on something that requires me to make one myself. With that being said, I'm having a ...
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### Can I derive the position of my house's shadow from sun altitude?

I'd like to pull in my awning if my house's shadow has reached a point where the awning has no use any more. The house is almost perfectly aligned in a North-South direction, the garden with the ...
29 views

### Position Angle Relative to North

I am trying to find the position angle of a star whose Ra and dec are known. I have already looked at the 'Measuring misalignment between two positions on sky' question and answer, but the answer ...
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### Looking for a Solar System Simulator including the smaller celestial body, for macOS

I am researching for a sci-fi novel that will happen in 2136. For this I would like to know specific positions of "smaller" celestial bodies in our Solar System. An example can be the dwarf planet ...
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### 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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### Galactic Equator zenith transit

I need to find the two times of zenith passage of the Galactic Equator for a given Earth Lat/Lon on any day between 3500 BC and 1500 AD. Since the Galactic Equator is a line and not a point, I try to ...
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### how to calculate distance between galaxies in the distant past

for example, assume there is a high redshift galaxy called "A" with z=6, so how to calculate the distance between us and another galaxy B when the light left the galaxy A? For example, say B has a ...
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### Visible satellites real time position API

I'm trying to obtain the azimuth and elevation of all (or at least the majority) visible artificial satellites from a given latitude and longitude. Is there a quite stable API that does that for free? ...
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### What book(s) should I read to get started learning about astronomy? [duplicate]

I'm an undergrad software engineer but I also love physics and math. I'm starting to get going in AI/Machine Learning techniques and I'm going to use NASA data-sets to conduct analysis. However, I am ...
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### What constellation is closest to the Zenith with RA=12 and Dec =47.6?

I have several options, but I do not know how to calculate which option is closest to the zenith in title. Could you please help me with this? Thank you. ...
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### Plotting Astronomical Data Using Python

I have been trying to create a graph which shows the distances between the stars and the earth, yet I could not obtain the desired graph as seen below (click to zoom in): My graph: As @uhoh ...
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### Help with Converting Right Ascension and Declination into 3D Vectors

Using the Right Ascension and Declination values from the HYG Database from The Astronomy Nexus: Right ascension is measured in hours and declination is measured in degrees. 1 - Convert right ...
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### Latitude of given altitude of Sun

From Question #6 of USAAAO First Round 2018 (1 point) For the following problem find the range in which the answer lies: on the day of summer solstice, on which geographic latitude is the sun ...
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### Galactic Coordinate System and distance

If the Galactic Coordinate System is made up of two values, angles of longitude and latitude, how is distance measured? If you have those two values, you get a line from the sun in a certain direction....
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### Are there any *client-side* JavaScript astronomy libraries? (not node.js)

Are there any client-side JavaScript astronomy libraries? Almost every library I see appears to be server side for node.js. I realize some node.js libraries can be adapted for client-side use, so I'...
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### Jean Meeus - calculating moon rise, transit and set times - help isolating error in logic

I've been working my way through the Jean Meeus Astronomical Algorithms book for a few weeks, to implement some of the key algorithms for a personal project. This task has been a little more complex ...
88 views

### ra for sun vs stars

There is formula for stars sideral time: $$ra - \arccos(-\tan(dec)*\tan(lat)).$$ where $ra$ - is right of ascension at the vernal equinox. $lat$ = latitude $dec$ = declination Is it applicable ...
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### Could someone please explain to me how I can extract velocity component values from Stellarium, for a given planet?

For a project that I am currently working on, I would like to know how one could extract velocity component values ($v_x$, $v_y$ and $v_z$) for a planet from the Stellarium software. The current ...
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### Sky from Equator at 8,000 years Before Present?

The Stellarium software allows future views of the sky. I need an online resource (planetarium projector?) that shows pre-historical views, and from the Equator at 8,000 years before the present.
262 views

### Planets positions (azimuth, altitude) API

I'm looking for a simple API that will allow me to get positions of planets and the moon for a given date, location and time. Does anyone know an API like that? Any suggestions or alternatives would ...
490 views

### Can Eight Retrograde (seen from Earth) planets occur?

First of all, for the purposes of this question Pluto is a planet. So the eight planets being considered are Mercury, Venus, Mars, Jupter, Saturn, Uranus, Neptune and Pluto. My question is: can all ...
117 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 ...
226 views

### evaluate solar eclipse Besselian elements? [closed]

I found this NASA website which says that to predict eclipse, we should solve the Besselian elements ..what does this mean, how can I solve for Besselian elements? Is there a numerical method? I need ...
106 views

### How to calculate planetary positions hundreds or thousands of years ago

Wondering how to calculate the following in a general way: Sunrise/sunset Equinoxes/solstices Moon phases Planetary positions For hundreds to thousands of years ago. Wondering what the calculation ...
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### How should I think about sunlight for the purposes of analyzing the angles it makes w/ earth?

Most diagrams I see of sunlight look like something like this: . They show that for basic geometric analyses, the sun's radiation can be thought of as 'thin lines' that strike earth. Further, at an ...
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### Geographical Point of the Sun

I want to draw a Sun in a 3d scene, so I figured the easiest way would be to calculate the latitude and longitude of the point perpendicular to Sun position and then just move it "up". As a starting ...
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### Is there any star recognition framework/library available?

Being a daytime software engineer and a sparetime photographer, I was looking for a nice DIY project for the next weeks. I finally decided to build a star tracker with a camera mount, so that I can ...
86 views

### The Sun and Regulus together at the summer solstice

Viewed from Stonehenge, when did the Sun and Regulus rise together at the summer solstice? Also when did Regulus rise before the Sun and would have been seen before the dawn glare?
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### How to get the solar zenith from the longitude and latitude?

I have real data of āDirect Normal Irradiationā and āDiffuse Horizontal Irradiationā and I should calculate āGlobal Horizontal Irradiationā. I have also longitude, latitude and elevation. Could you ...
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### Where on Earth can moon rise on the meridian?

Somewhat related to this my picture showing only diurnal motion but Moonāseen from Earthāhas a rapid motion with respect to the inertial celestial sphere, unlike stars and planets. Its motion relative ...
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### Is Spherical Astronomy by W. M. Smart a good book on positional/spherical astronomy?

I'm a math undergrad, but I'm really interested in learning positional astronomy; However, the only well-referenced textbook I've come up with is Spherical Astronomy by W. M. Smart. I would like to ...
295 views

### How do I make a custom pulsar map?

I'm looking to make a custom pulsar map like the one on the Voyager Records, but for an arbitrary location within the Milky Way Galaxy. I'm not even sure where to begin.
146 views

### Angular speed of a planet across the sky

Assuming circular orbit, the evaluation of the angular speed of a planet around the Sun, just requires its orbital period. Similarly, to calculate its angular speed relative to the Earth (also seen ...
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### Synodic period of planets

Many books explain the difference between synodic and sideral periods. The synodic period of planets are tabulated for centuries and it is defined as the time interval between two consecutive ...
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### Error when calculating Alt/Az from Ra/Dec

I wrote a program based on this tutorial: http://www.stjarnhimlen.se/comp/ppcomp.html to calculate altitude and azimuth of a celestial object. When I compare the calculated RA/Dec values to the ones ...
129 views

### Is it possible to define a state of zero absolute angular momentum anywhere in the universe?

Conservation of angular momentum doesn't seem correct to me. I think this because radiation is present everywhere, no space is completely void, and no object perfect. Thus all objects will have uneven ...
856 views

### How to construct a sky map

First of all, I have very basic knowledge of astronomy so sorry if I make some mistakes in my terminology. I'd like to plot the Southern Cross. I can find the name of its 5 stars. Also, I have some ...
217 views

### Heliocentric distance from galactic x y and z coordinates

How can I get heliocentric distance to a star when I have galactic x y and z coordinates known ?
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### Generate an uniform distribution on the sky between limits

I have an analog question of this one : Generate an uniform distribution on the sky I generate an uniform distribution on the sky, but just a patch of it, with \alpha_{min} \leq \alpha \leq \alpha_{...
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### What are the problems that need to be taken in consideration when trying to find planetary position by using jpl ephemerides?

I'm currently trying to determine the position of the sun and the moon from jpl ephemeris DE200 which is referred to the dynamical equator and equinox of 2000 and uses tdb time. I am using the j2000 ...
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### Formula for sun's atmospheric refraction below the horizon

I have searched in Google and found interesting articles for atmospheric refraction influence on sun's elevation above the horizon (from 0Ā° till 90Ā°). eg. Bennett G.G. etc. I would like to know if ...
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### Given sunrise, noon, sunset, longitude and latitude can I calculate the “hight” or “ascension” of the sun?

I'm trying to make a simple app for my own use to be able to check which of my favorit restaurants have outdoor seating sun and for how long etc. Given the data in the title (sunrise, noon, sunset, ...
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### How could I determine what areas of the Milky Way will be visible?

There is a new moon on Saturday, and the forecast in my area of Winnipeg, Manitoba, Canada calls for clear skies on that night. I would like to take a widefield astrophotograph. I have no idea what ...