31
votes
How to describe the Sun's location to an alien from our Galaxy?
This has already been done. The pioneer 10 and 11 probes have a description of the solar system's location and Earth engraved for aliens to understand (or so one hopes). The physical parameters of our ...
- 17.6k
13
votes
Accepted
How to describe the Sun's location to an alien from our Galaxy?
If the travel was instantaneous (or say, less than a million years) it should be relatively easy to relocate the Sun from triangulation using well-known objects visible from anywhere in the Galaxy. If ...
- 146k
9
votes
Accepted
How can non-earth-orbiting satellite coordinates be obtained by amateurs?
Does a publicly accessible website/API exist that provides the current coordinates for such objects?
Yes! There's a pre-launch planning trajectory from ISRO/JPLNAV in the Horizons system. Chandrayaan-...
- 13.1k
7
votes
Difference in results between JPL Horizons and cspice (rust-spice)
The issue is with how you have configured HORIZONS to show the output. You have apparent RA, Dec selected as output columns which includes the precession and nutation, in addition to the light time ...
- 8,313
6
votes
How to describe the Sun's location to an alien from our Galaxy?
Since you're talking about aliens in our galaxy, I think the question comes down to whether we would expect the aliens to have a map of our shared galaxy which is sufficiently similar to our map that ...
- 211
5
votes
Accepted
How to calculate distance between stars?
This can be done straightforwardly without even thinking about the geometry if you convert to Cartesian coordinates. Given a star at distance $d$, galactic latitude $b$, and galactic longitude $l$, ...
- 4,260
5
votes
How exactly is UT1 measured/calculated?
("How exactly is UT1 measured/calculated?" -- with "interest in fine details about how UT1 time is measured.")
(edited 2023/Mch/27 to add references including text+image extract of ...
- 1,329
4
votes
How to plot object on the map correctly
No, it's not enough. The coordinates you give are the position in the sky. To plot a location in the galaxy, you'd need also to know the distance from Earth.
However, nearly all naked eye visible ...
- 116k
4
votes
Accepted
Are the rotational axes of Earth and Mars parallel?
The polar axis of Mars is not parallel to the polar axis of Earth. The north celestial pole of Earth has a declination of 90°, but the north celestial pole of Mars has a declination of almost 53°.
...
- 13.1k
4
votes
What does Ptolemy mean by "a line drawn from the centre of the earth through the centre of the moon to a point on the ecliptic"
In his model, Ptolemy considered the ecliptic to be the path of the Sun—hence, a distinct circle than the path of the Moon. In modern terms, one could say that Ptolemy thus (rightly) considered the ...
- 6,701
4
votes
Accepted
Drawing stars in a 3D space
You can't without knowing the distance to the star, $d$.
Once you have that then, depending on exactly how the $x, y, z$ axes are defined:
$$
\begin{align}
x &= d \cos(b)\cos(l) \\
y &= d \cos(...
- 146k
4
votes
Accepted
Discrepancies in the equations for converting Horizontal coordinates to Equatorial coordinates
According to the old nomenclature, the azimuth $A_s$ was defined starting from the South towards the West, from 0º to 360º (SWNE direction).
If $a$ = altitude, (not zenith angular distance = $z$) and $...
- 1,720
3
votes
Accepted
Reverse polynomial model for reverse astrometry
There is a fundamental mathematical problem that on paper is devastating and in practice irrelevant: there might not be any inverse, since clearly the $\eta=f(x,y)$ polynomial equation can have ...
- 14.3k
3
votes
Reverse polynomial model for reverse astrometry
Thank you all for your solutions and suggestions. During testing of Anders Sandberg solutions I've thought of another idea. I can calculate $\xi$ and $\eta$ directly from equatorial coordinates and ...
- 195
3
votes
If Sagittarius A* were used as a compass, where would its points be?
From Earth, we cannot see any objects directly behind the Milky Way's center (at the center of the Zone of Avoidance), so we don't have any known objects available to define North in the new compass ...
- 131
3
votes
Accepted
Transformation of hour angle to azimuth
You can use the signs of the $ sin A $ and $ cos A $ to determine the proper quadrant:
The equations in the Explanatory Supplement to the Astronomical Almanac are slightly different than the ones ...
- 5,562
3
votes
Pleiades galactic coordinates
You can use a coordinate converter, such as the one found here to change from RA, Dec to $l, b$.
The coordinates of an object do not directly tell you whether something is a thick/thin disk object, ...
- 146k
2
votes
How to calculate planetary aspects at a stationary point?
There is software for calculating planetary aspects which is based on the JPL ephemeris -- https://ssd.jpl.nasa.gov/horizons/ It calculates geocentric planetary positions, and aspects between planets,...
- 21
2
votes
Horizontal to Equatorial Conversion - Code
Only took three years, but finally worked it out. This is in rust but the formula is in there.
...
- 131
2
votes
Accepted
Calculate declination of Galactic N. Pole given obliquity of Ecliptic, rt. ascension of Galactic N. Pole, & angle between Galactic & Ecliptic Pole
With the substitutions:
$$
\begin{align}
a &= \cos{23.43928°} \approx 0.9174821
\\b &= \sin{192.8583°}\sin{23.439289°} \approx -0.0885216
\\\theta &= 60.2°
\end{align}
$$
I believe the ...
- 4,695
2
votes
Comoving distance between two points [(RA1, Dec1, z1) and (RA2, Dec2, z2)]
As per my understanding one can get the distance between two object using astropy function. like this
...
- 41
2
votes
Reverse polynomial model for reverse astrometry
If you have your SIP coefficients defined in a FITS header, this should be as simple as using the world_to_array_index_values() method of ...
- 1,084
2
votes
Accepted
How to find the numerical positions of objects in the sky?
Not really an answer to your question, but you may still find some of these resources helpful/interesting:
Where can I find the positions of the planets, stars, moons, artificial satellites, etc. and ...
- 31.4k
2
votes
How can non-earth-orbiting satellite coordinates be obtained by amateurs?
SPICE kernels are available for many NASA (and other missions). A large collection is available from NAIF. As well as some archived datasets. These can be processed using the SPICE toolkit, which ...
- 5,562
1
vote
How to describe the Sun's location to an alien from our Galaxy?
Some very interesting answers have already been given, but a specific sentence in your proposition makes me want to try a different approach.
If your consider this segment :
alien astronomers managed ...
- 11
1
vote
How to describe the Sun's location to an alien from our Galaxy?
The simplest is to treat the galaxy as a plane and use polar coordinates. The center can Sagittarius A* (which is a massive black hole at the center). For angle, you can exploit the asymmetric, ...
- 407
1
vote
How to find the numerical positions of objects in the sky?
Astronomical objects, including stars, planets and the surface of the Earth, move in a very regular and predictable way. This means that their positions can be calculated and predicted years (...
- 116k
1
vote
How to calculate distance between stars?
Part Oe of Five: An Online Dsitance calculator.
Here is a link to an online calculator that calculates the distance between two stars.
https://www.wolframalpha.com/widgets/view.jsp?id=...
- 7,411
1
vote
CSPICE vs JPL Horizons discrepancy in AZ/EL
Discrepancies of 0.000147842 degrees in AZ, and 0.00002705 degrees in EL.
Those discrepancies are very small; they are essentially the same numbers. There is one difference: your CSPICE calculations ...
- 33.5k
1
vote
Deriving orbital inclination from equatorial coordinates?
Orbital inclination can be estimated fairly well from two observations made when the planet is in opposition to the Sun. If the observation means/method gives equatorial coordinates they should be ...
- 1,608
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