Questions tagged [declination]

Questions regarding one of the two main angles(coordinates) of an object perceived by an observer on Earth.

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346 views

Straightforward derivation of the sunrise equation

I'm looking for a reasonably straightforward derivation of the sunrise equation$$\cos\omega=-\tan\phi\tan\delta$$as referenced in the Wikipedia article here. I've dipped into Astronomical Algorithms ...
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33 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 ...
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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 ...
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32 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
52 views

What is the longitude of the winter solstice for the various planets?

I am looking for data showing the longitude at which the various planets in the solar system reach their winter solstice. Where could I find this data?
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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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2answers
111 views

Solar Azimuth angle Derivation

I tried posting this on math stack exchange to no avail so I thought maybe it's more relevant here : I know a similar question has been posted here before but no links to any mathematical derivations ...
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1answer
127 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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1answer
156 views

How to manually locate a certain declination in the sky for a given location? (no sextant available)

Consider this example. I am standing in a flat surface, at latitude X, looking to the equator, in a random day of the year. (For simplicity, let's assume X > 23.5º) I want to find the position of ...
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1answer
36 views

How can I find a date when the moon at zenith over a specific spot on the equator?

I would like to know when the moon is directly overhead 0° S, 166° E. Are there any websites that will show me any of those dates?
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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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105 views

A Noob's question on declination

The Sun's position at noon is perpendicular to the local x-y plane on the equator during equinox. So the declination of Sun on that day is 0. Today the declination of Sun is close to 23, can this be ...
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312 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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324 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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351 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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678 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 ...
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1answer
150 views

How to compute Ascension / Descension cycle of the Moon

I am struggling to find out an information about how to determine ascending/descending cycle of the Moon. I can find from this source and a bunch of others, that Moon begins to descend when reaches ...
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1answer
379 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 ...
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1answer
74 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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569 views

Planetary Declination and Axial Tilt

Is it a coincidence that Earth's axial tilt and maximum declination are both approximately 23 degrees? Mechanically speaking, do planets physically cross the Solar equator, or is declination due to ...
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945 views

How do you draw the ecliptic on a celestial sphere sketch?

I don't really understand how it's drawn on sketches of the celestial sphere. At first I thought it goes through east and west, but it does not. How do you know where to draw it? Example from Roy and ...
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995 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
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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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1answer
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How to calculate declination of Moon?

Is there any way to calculate declination of Moon for any day?I'll subtract inclination of Earth on the ecliptic from the result. I'll get Moon's the shortest angular distance from Sun. Thanks for all ...
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1answer
219 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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402 views

Precise declination of Moon

The moon follows 5.14 deg inclined path. the ecliptic and the Moon's path coincide are called 'nodes', and they travel around the ecliptic in a period of 18.66 years. Once every 18.66 years, the ...
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Where on Earth can moon rise on the meridian?

Somewhat related to this my picture showing only diurnal motion but Moon—seen from Earth—has a rapid motion with respect to the inertial celestial sphere, unlike stars and planets. Its motion relative ...
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1answer
270 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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115 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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1answer
369 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: ...
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337 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 ...
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3answers
460 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 ...
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1answer
940 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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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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62 views

Sun's position on summer solstice

Let's say I am in Brasilia (latitude = 15.78°S). This is obviously south of the equator but north of the tropic of capricorn. So on the summer solstice I know that the Sun's declination is +23.26°. ...
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1answer
433 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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1answer
188 views

Measuring declination in negative hours of arc?

I'm running the program found at https://www.projectpluto.com/source.htm in order to find the Right ascensions and declinations of celestial bodies at various points in time. An odd thing I've noticed ...
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428 views

Nodes and declinations of Moon

This nice page from NASA has the possibility to create an astronomical events calendar for a certain period. I tried to do that for the year 2017 for Central Europe. What comes out puzzles me: On ...
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1answer
883 views

Is there a difference between the solar elevation angle and sun declination?

I need to use the sunrise equation but one of the variables is the sun declination. On the other hand, I have the values for solar elevation angle that I need. Are they the same thing?
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Ecliptic plane, its precise definition useful for calculations

My question is similar to the one posted by Abtract, whom however never got a useful answer. I am trying to calculate from scratch the exact times of sunrise and sunset anywhere on earth taking into ...
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1answer
589 views

Where is 0 R.A.?

If declination is the degree measurement from the celestial equator roughly the Earth equator unless I've misunderstand plane. "The celestial equator is a great circle on the imaginary celestial ...
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1answer
110 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 ...
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Why are tides biggest during the equinoxes?

I've read that during the equinoxes, tides are at their maximum. Shouldn't this only apply to latitudes near the equator? I mean, when the solar declination is near to 0º and we have a full or new ...
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an exercise from Spherical Astronomy by Smart

I want to solve this exercise from Spherical Astronomy by Smart: Prove that, in latitude 45°, the interval between the moment at which a star's azimuth is 90° east and the moment of setting is ...
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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, ...
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1answer
2k views

Calculating Right Ascension and Declination from Latitude / Longitude / Time

I have a latitude / longitude / time of a location on Earth, I need to calculate the Right Ascension / Declination that's overhead at the time provided. So far I've found out that Right Ascension is ...
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120 views

Why is declination positive in the northern hemisphere?

Simple question -- why is declination positive in the northern hemisphere? Seems like it should've been called "inclination" since the word originated north of the equator.
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Declination change due to precession

I have this problem: I want to calculate the declination of the star in the year 5000. And I know RA (right ascension) and Dec (declination) of the star right now. How can I calculate it using ...
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1answer
1k views

How to find maximum and minimum right acsension and declination based on the telescope's location?

If I am to apply at a telescope for viewing objects, how to determine (easily) what is the minimum and maximum possible RA and DEC visible from that telescope during that time of the year. For eg, ...
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Low precision GMST formula clarification

According to the website http://aa.usno.navy.mil/faq/docs/GAST.php, a low-precision way of calculating the GMST is via the following formula: GMST = 18.697374558 + 24.06570982441908 D The website ...