Questions tagged [declination]
Questions regarding one of the two main angles(coordinates) of an object perceived by an observer on Earth.
77
questions
4
votes
1
answer
271
views
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 ...
0
votes
0
answers
94
views
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 ...
1
vote
1
answer
39
views
Definition for Day Angle
I am searching for a proper definition for day angle.
The day angle $\Gamma$ is calculated as follows:$$\Gamma = 2\pi\cdot \frac{n_{day} - 1}{365}$$
1
vote
0
answers
76
views
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 ...
2
votes
1
answer
90
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?
0
votes
0
answers
35
views
What is the declination of the Sun as a function of its angular distance to solstice?
I will show my own answer, hoping that you guys either confirm it or show me where I went wrong.
First, let's have in mind that we are not concerned with the distance Sun-Earth, only with the angle. ...
2
votes
2
answers
199
views
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 ...
2
votes
0
answers
104
views
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 ...
4
votes
2
answers
144
views
Why isn't Amplitude the same as Declination?
From the way I understand Amplitude and Declination, it seems to me that they should always be the same, yet they are not, why?
P.S. In the picture I am imagining that the declination remains constant ...
1
vote
1
answer
99
views
Meaning of $\cos H$ in the rising and setting formula
In the rising and setting formula$$\cos H=-\frac{\left(\sin\nu+\sin\phi\sin\delta\right)}{\cos\phi\cos\delta},$$ $H$ is hour angle, $\nu$ is vertical shift, $\delta$ is declination and $\phi$ is the ...
1
vote
1
answer
100
views
What is the "sunrise equation" for non-constant declination component?
The standard Sunrise Equation (refraction neglected) is this:
$$ \cos(\text{hour angle}) = \tan(\text{declination})\tan(\text{latitude}) $$
This equation - which really has nothing to do with the Sun ...
5
votes
1
answer
506
views
When was/will Polaris's declination be maximised?
When was/will Polaris's declination be maximised?
In what year was/will Polaris be closest to the north celestial pole.
2
votes
0
answers
170
views
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 ...
17
votes
2
answers
3k
views
On Mars, why are the seasons "strongly amplified" in the southern hemisphere and masked in the northern hemisphere?
In the Darian calendar entry on Wikipedia we read (emphasis mine):
The Martian year is treated as beginning near the equinox marking
spring in the northern hemisphere of the planet. Mars currently ...
4
votes
2
answers
674
views
Deriving the apparent angular speed of a star
The angular speed of stars in the sky is constant but the apparent angular speed is not, due to the star moving faster on the celestial equator and slower near the celestial pole. The apparent angular ...
1
vote
2
answers
165
views
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 ...
3
votes
1
answer
264
views
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
1
answer
242
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 ...
4
votes
3
answers
706
views
How to calculate the nodal precession range of the Moon with respect to the celestial equator?
In the span of 18.6 years there is nodal precession of the Moon with respect to the ecliptic of 360 deg. But if we consider this precession with respect to the equator, we will find (unless I'm hugely ...
1
vote
1
answer
77
views
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
1
answer
420
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 (...
5
votes
1
answer
1k
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 ...
0
votes
1
answer
624
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
votes
2
answers
1k
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 ...
0
votes
1
answer
213
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(...
3
votes
1
answer
66
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?
0
votes
1
answer
537
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 ...
4
votes
3
answers
924
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 ...
0
votes
1
answer
1k
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 ...
2
votes
1
answer
204
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 ...
1
vote
1
answer
250
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?
5
votes
2
answers
640
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 ...
1
vote
1
answer
111
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 ...
0
votes
1
answer
1k
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, ...
3
votes
1
answer
1k
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 "...
0
votes
1
answer
1k
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 ...
2
votes
1
answer
1k
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 ...
1
vote
1
answer
337
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 ...
2
votes
1
answer
1k
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
votes
1
answer
108
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 ...
2
votes
1
answer
1k
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 ...
0
votes
2
answers
1k
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 ...
2
votes
3
answers
2k
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 ...
2
votes
1
answer
7k
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 ...
1
vote
1
answer
3k
views
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 ...
3
votes
1
answer
399
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
...
2
votes
1
answer
1k
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 ...
2
votes
0
answers
96
views
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 ...
1
vote
1
answer
592
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 ...
1
vote
1
answer
190
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 ...