Questions tagged [right-ascension]

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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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322 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 ...
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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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1answer
120 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 ...
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179 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 ...
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83 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 ...
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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: ...
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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 ...
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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 ...
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587 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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513 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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238 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: ...
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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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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 == ...
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351 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 ...
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144 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 ...
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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 ...