# Questions tagged [right-ascension]

Questions regarding the second ordinate of the equatorial celestial system.

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### Hour angle to Right Ascension correct when the longitude is positive

I'm developing a Astronomical software using the formulas from the book: "Practical astronomy with your Calculator and Spreadsheet", but I'm having some problems to get the right ascension ...
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### calculate declination and right ascension with limited information

I'm trying to make a game with high accuracy moon position so I followed some equations on geoastro.de Basics of Positional Astronomy and Ephemerides and with some help from the questions answers, I ...
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### Position of Hamal (alpha Arietis) between 1582 and 1588

Between 1582 and 1588, Tycho Brahe observed $\alpha$ Arietis from Uraniborg (55°54′28″N 12°41′48″E) on at least 27 separate occasions and made a record of the right ascension of the star (see Opera ...
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### Sidereal time of rising and setting of the sun on the arctic circle

$$cos(h)= -tan(\delta)tan(\phi)$$ $$\Theta = h + \alpha$$ if these two equations are the correct equations to solve the following question why doesnt it yield the same answer for the sideral ...
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### How to even approach this type of question

Can someone tell me how one would approach this type of question. is there an equation we would use or something of the sort. Ths solution to this question is given below but I just want to understand ...
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1 vote
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### Plotting galactic latitude in Ra vs Dec plane

I have an open cluster with calculated percentage of polarization and position angle. I want to have it's scatter plot in Ra vs Dec plane and superimpose a galactic parallel on it. How to plot the ...
171 views

### Does RA/Dec vary with the Earth's orbit around the Sun?

I think the RA and Dec of a celestial object should change (ever so slightly) with the Earth's position in its orbit. So do we ignore this in general?
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### How to convert GMST to GMST° (degrees) for calculating RA [duplicate]

For calculating the Right Ascension of the moon I need the GMST (Greenwich Mean Sidereal Time) in Degrees. I have found the formula GMST = 100.4606184 + 0.9856473662862 * D + H * 15, D = number of ...
1 vote
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### Convert RA from hours to h:m:s

I'm working on a small mount controller software in Python. From the ASCOM standard, right ascension is reported in unit of hours. How do I convert from hours to hours:min:sec? Here is my attempt in ...
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### How to calculate Local Sidereal Time from RA of a star and Longitude of Observer

I have been banging my head against a wall trying to understand these time conversions and the relation between all of these astronomical measurements. This is the question I am currently working on, ...
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### How to get the right ascension of the Moon?

Is there any approximate way to calculate the right ascension of the Moon? I already got declination but still, need the right ascension to calculate the final position of the moon. Thanks for all ...
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### Right ascension and declination visible at that local time and location

If I know the local time of an observer and her/his latitude and longitude, how can I know which stars are visible? I'm developing a planetarium software using the Hipparcos Catalogue. I have also ...
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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 ...
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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 ...
1 vote
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### How to calculate the local time of sunrise and azimuth of rising point of Sirius?

I know that right ascension equals to $6^h45^m$ and declination equals to $-16°43'$. I need to calculate local time of sunrise and azimuth of rising point of Sirius on 23 of September for an ...
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### 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 ...
1 vote
340 views

### At what rate does the right ascension and declination of a planet, the sun and moon change per hour?

I'm currently building a web app and am getting the RA's and Dec's of solar system objects based on date and time chosen by the user. Then using the gmst for 0 hours of the date, the app calculates ...
1 vote
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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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### Is the Ra/Dec of Alnitak in Orion's Belt known to be correct?

I've obtained right ascension / declination information about some of stars in the Orion constellation from a few different sources and imported this into an open source video game I'm making. Using (...
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### Sun right ascension and declination at date with different values on different calculators and also with my implementation

I'm reading the book "Practical Astronomy with your Calculator or Spreadsheet 4th Edition" implementing its formulas with C++. Now, I have implemented formula 47 "Calculating orbits ...
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### What is the rate of change by day for a given right ascension?

I am writing a small Julia app to get my feet wet in that language. And I want to calculate "what's up tonight" based on a table of right ascension (RA)/Dec(lination) (table of stars), a ...
286 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 ...
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### What's the difference between minutes and arcminutes?

I read in trigonometry class that 1 minute is equal to 1/60 degrees. So, 'minute' is an angular unit. But also 'arcminutes' are used to measure seperation between celestial objects and also equals to ...
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### RA and Dec of Near-Earth-Objects

I'm new to the forum. This might be a silly question. I had a confusion about how RA and Dec are calculated. So, from what I understand RA is the angle made by the position vector of an object(...
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### How can you find the distance to a galaxy using right ascension and declination?

For example, Galaxy NGC 3689 has the right ascension of 11:28:11 and declination of +25:39:40.0. Using these values, how can we find the distance to the galaxy? If it helps, its radial velocity is ...
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### Right Ascension of North Celestial Pole

My scope simulator is pointing to the celestial north pole. My position is 41º 27' lat and 2º 15' long. At 12h 43m local time (11h 43m UTC) the coordinates read from the scope are: RA: 16h 14m 25s DE: ...
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### How to convert Proper Motion in RA & Dec to Galactic Coordinates

I'm trying to parse stellar data in the GAIA 2 release to galactic coordinates and am struggling with the velocity component. I've tried following online documentation and papers, but end up with ...
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### Calculating the time a star is at my local meridian based on its right ascension

I've been watching an astronomy course on YouTube and I'm struggling to calculate stars' positions based on their right ascension. What I'm trying to achieve: Calculate when a star (Sirius in this ...
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### What is the area of the Summer Triangle?

I'm pretty sure spherical trigonometry comes into use here but I don't know how to calculate the area. I'm pretty sure Vega, Deneb, and Altair's declination and right ascension figures need to be ...
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### How can I calculate the right ascension of an observer on Earth's surface in the TEME frame with python.skyfield?

I would like to calculate the right ascension of a point on earth as specified above with the Skyfield Python library, and I can not figure out how to do this. I know that calculating the geocentric ...
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### Correct units to use while plotting mollweide projection of sky chart with RA and Dec values, matplotlib

I am trying to plot a mollweide projection of a sky chart in Python using the matplotlib package. I am using the RA and Dec values from a database containing all stars in Hipparcos, Yale Bright Star, ...
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### Right ascension and sidereal time difference

I've read quite a few articles about this and watched visualisations but I still struggle to get a mental map of how this works I understand that on March 21/22 RA 0 is on my meridian at local noon. ...
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### Is the vernal equinox always in zenith somewhere on the equator?

I'm trying to visualize the satellit orbital parameter "right ascension of the ascending node" (RAAN). Measuring the angle from the vernal equinox to the point where the satellite's orbit crosses ...
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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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### RA and Dec of the Sun at J2000

I'm in the somewhat awkward position of asking something that, despite me thinking there should be hundreds and hundreds of web pages and datasets showing this particular value, I've been unable to ...
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### Right Ascension to Zodiac House

At the moment (01-04-2020 09:36) the Moon is situated in Gemini: "The Moon is currently in the constellation of Gemini. The current Right Ascension is 06h 37m 56s and the Declination is +23° 42' 09”."...
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### Deducing the hour based on RA

I'm making a technological project. The goal is to write a program that gets an image of the nightsky and predicts the hour in which the photo was taken. I implemented a well-known method using the ...
1 vote
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### What is the opposite of the vernal point?

The equator and the ecliptic cross at two nodes. One of those nodes is the vernal point. What is the other one called?
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### how to plot sky map like www.nakedeyeplanet.com with dates tags with planetary motion path

I am curious how to plot planetary motion star chart with date tags like on www.nakedeyeplanets.com by Martin J. Powell. Is there any way to generate images similar like that. What software should ...
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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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### How can I check if we can observe a certain star (given its equatorial coordinates) from a certain location on Earth (given its DMS coordinates)?

I am given the equatorial coordinates of a star (e.g. Sirius has RA: 6h45m8.9s and Dec = -16°42'52.1"). Now my question is: can we observe this star from a specific location on Earth (e.g. from ...
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### Date and Time of Year given Sun's Right Ascension

Can anyone tell me how to calculate date of year given a specific sun's Right ascension (RA)? I know RA at Vernox (21 March 00hh:00mm:00ss)is 0 degrees. How can I get date and time for a given RA, ...
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### Right Ascension for epoch 2000 - physical location?

I understand that Right Ascension is a longitude-like celestial coordinate that varies from 0-24hrs, taken from a reference point of the vernal equinox. More specifically, for star maps that are based ...
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### What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?

@MikeG's answer to Why does this Lowell Observatory telescope have so many knobs? What do they all do? explains that item #6 labeled in the image there (and cropped version here) is likely to be a "...
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### How to calculate solar coordinates. (Right Ascension, Declination, and ultimately the Altitude and Azimuth of the Sun)

As the title says I am trying to calculate solar coordinates of the sun for a given location and time. I have spent many 10's of hours on this without success so I will sincerely appreciate help on ...
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### How to calculate the ground track of the Moon's position on the Earth's surface?

I would like to project the Moon's position on to the surface of the Earth, starting with its position expressed as Right Ascension in degrees. I know that the declination of the Moon corresponds to ...
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### Moon equatorial coordinates

It took some effort, but in the end, I successfully calculated the geographical point of the Sun. I assumed that I could do the same for the Moon. My plan is: Find RA and declination of the Moon ...
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### How to calculate the time and distance of closest approach of a star?

How should I approach this problem? A star has a motion on the sky of 0.78 arcsec/yr in declination and 1.33 arcsec/yr in right ascension. Calculate the velocity of the star in the plane of the sky ...