Questions tagged [right-ascension]
Questions regarding the second ordinate of the equatorial celestial system.
44
questions
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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 ...
7
votes
1answer
299 views
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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1answer
51 views
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 ...
3
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2answers
119 views
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 ...
3
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1answer
150 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 ...
18
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4answers
3k views
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 ...
0
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1answer
51 views
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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1answer
143 views
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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1answer
179 views
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: ...
0
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1answer
173 views
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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3answers
588 views
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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2answers
590 views
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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1answer
161 views
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 ...
0
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1answer
451 views
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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1answer
499 views
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. ...
2
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1answer
200 views
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 ...
3
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1answer
405 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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1answer
446 views
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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2answers
592 views
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”."...
3
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1answer
87 views
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 ...
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0answers
81 views
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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1answer
782 views
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 ...
2
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1answer
490 views
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 ...
2
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1answer
80 views
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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342 views
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, ...
4
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2answers
840 views
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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0answers
66 views
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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2answers
1k views
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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1answer
4k views
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 ...
3
votes
1answer
239 views
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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1answer
334 views
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 ...
2
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1answer
427 views
Calculating right ascension for two planets and their separation using python
I am experimenting with the Python library PyEphem for astronomy, and I am trying to recreate/understand some of the basic calculations there.
There is a function called separation that, given two ...
0
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1answer
132 views
angles on the celestial sphere
This is a somewhat simplified, and drawn / formulated in a manner more targeted to astronomy, version of a diagram and a question that I've also posted in math.stackexchange.com.
In the diagram below ...
2
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1answer
401 views
Presenting / printing Right Ascension and Declination values
Are there any standards or established practices on how to write / represent Right Ascension (RA) and Declination (DEC) values in the sexagesimal format?
I have seen all of the following. E.g. for RA:
...
0
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2answers
368 views
When does a star rise with the sun?
Problem: Suppose an observer's latitude is 45 S and a star's RA/DEC is
3h15min/41S. On what date will the sun set with the star.
I have been stuck on this problem for a while.
I found out that the ...
4
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3answers
528 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 ...
3
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1answer
1k views
Declination calculation
My task is to calculate current declination and right ascension for some artificial Earth satellite. For example ISS.
I am using latest TLE data for extracting keplerian orbital elements and then ...
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1answer
1k views
Convert a Decimal into RA or Dec
http://exoplanets.eu/ displays R.A. on screen in hh:mm:ss format but when you export the table, it gives the R.A. as a decimal. Likewise for Declination.
How can I turn for example 24.35417 (WASP-...
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1answer
449 views
Using setting circle for Right Ascension
I'm a little bit confused about the setting circle of my EQ5 mount. Basically, I'm trying to find M42 nebula using Sirius star as reference. So, considere that I did the following steps:
...
0
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2answers
124 views
Distance from W(West) to vernal equinox
I am pretty new to astronomy and the project I am currently working on requires some knowledge of equatorial coordinate system.
As long as I have been researching this question, I understood that ...
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1answer
75 views
How are the days relating to right ascension around a polar star chart decided?
If you look at this link they have days realting to right acension.
How did they calculate nov 20th == 0h, dec 6 == 1h?
I was trying to calculate this in astropy, but I end up with nov 20th, 8pm == ...
0
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1answer
642 views
What is the right ascension overhead at Greenwich at noon on 21 march
My question is seen in the title: What is the right ascension overhead at Greenwich at noon on 21 march
I'm a little bit confused since the right ascension is set by the vernal equinox and don't ...
0
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1answer
245 views
Sidereal time and right ascension
I'm new to astronomy and have to make a star map that displays the stars above a current location. From the information I've pieced together I understand that declination is equal to the current ...
2
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1answer
111 views
Centre (projected) of a galaxy cluster
A galaxy cluster consists of somewhere around a few tens to several hundred galaxies.
To measure the position of a galaxy cluster, i.e. it's RA and DEC, do astronomers always assume it to be its ...
