# Questions tagged [positional-astronomy]

Questions about positions of objects in the sky, either relative to a fixed coordinate system like the equatorial and ecliptic coordinate systems, or relative to an observer's point of view.

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### How to plot right ascension with time of the retrograde motion of mars? [closed]

Measure the right ascension, declination of mars and sun. plot the variation of right ascension with time. 28 views

### Longitude from different vantage points

Given, the mean longitude L of the Earth-Moon barycenter, as seen from the Sun's center. From this, is the mean longitude of the Sun L+180°, or is it 360°-L, as seen from the Earth-Moon barycenter? ...
520 views

### Difference in results between JPL Horizons and cspice (rust-spice)

I am calculating the apparent planetary position of planets using the cspice library (I am specifically using rust-spice, which is a wrapper of cspice in Rust). when I calculate the same values in the ...
135 views

### Calculating Position of Sun in GPS Frame Relative to 0°00'00.0"N 0°00'00.0"E: Determining Vernal Equinox Offset

I am trying to calculate the position of the sun, in GPS coordinates terms, from a given date. As of right now, I know how to accurately calculate the equatorial Right Ascension and Declination, and ...
1 vote
56 views

### Transformation matrices and their derivation (if possible) for ICRS frame for reference to other frames

I am finishing up my thesis write up and one of the chapters in my thesis is on astronomical coordinate systems since in my analysis of data I have converted the available astrometry from the ICRS ...
319 views

### Why don't we use the Voyager/Pioneer etc space probes to measure stellar parallax?

With Earth based telescopes you get a max distance of 2 au between measurements. While we have multiple space probes well over 100 AU away from us, that's a 2 OoM difference.
136 views

### Angular distance calculation in Equatorial and Galactic coordinates

I calculated the angular distance between the Galactic Center and Andromeda in Equatorial and Galactic coordinates and observed that the distance is calculated differently depending on the coordinate ...
80 views

### Find position of orbiting body along orbit efficiently

I'm coding a game, and a fundamental mechanic is celestial bodies moving in elliptical, Keplerian orbits around a single gravitational point in a planetary system (not our solar system). The bodies ...
121 views

### Discrepancies in the equations for converting Horizontal coordinates to Equatorial coordinates

Hello I am trying to convert my Horizontal coordinate system dataset into Equatorial coordinate system. However, it seems that all the information from the internet is different. I will use symbols as ...
2k views

### What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond?

My son and I are building an azimuth/elevation controller to point the telescope at planets using servos and a microcontroller. Assuming that our device is calibrated (that is, we tell our device to ...
2k views

### How can I convert my sky coordinate system (RA, Dec) into galactic coordinate system (l, b)?

I am an astro-particle physics PhD student trying to look for a simulation. I was looking for a conversion formula for sky (or celestial or Equatorial) coordinate system using Right Ascension and ...
1 vote
95 views

### Calculate declination of Galactic N. Pole given obliquity of Ecliptic, rt. ascension of Galactic N. Pole, & angle between Galactic & Ecliptic Pole

I’m trying to back-calculate a value in astronomy using spherical trigonometry. (This is not a homework problem, I'm retired). Using the following formula, where δ = the Declination of the Galactic ...
215 views

### CSPICE vs JPL Horizons discrepancy in AZ/EL

This CSPICE spkcpo_c routine example outputs: ...
284 views

### How to calculate Local siderial time that is consistent with Stellarium

I have a number of date and times when I am interested in the location of my zenith and what objects might co-locate with these positions. The easiest way to do this was to put my latitude and ...
86 views

### How can we make sure that it is physically the same source when we do cross matching?

When we go through multiple astronomy catalogs, we often do Cross-matching. We compare the position parameters $(\alpha, \delta)$ of different sources (galaxies, quasars, etc.) in the equatorial ...
1 vote
23 views

### calculation of observers latitude, first vertical

In an exercise, I have to calculate the observers latitude. Given are the altitude a of the star at the passage through the first vertical (Azimuth = 90°/-90°), the sideral hour, the right ascension, ...
84 views

### How to know if the star is on the west or east side calculating hour angle and sideral hour

I have an exercise where I need to calculate the hour angle (H), declination (δ), latitude (φ) and the sideral hour at the moment the star passes through the 18 hour circle. Given are the right ...
54 views

### You find yourself on a random planet in the milky way 2000 years in the future. Can you figure out where/when you are? [duplicate]

Imagine you're on a planet in a distant part of the milky way, 2000 years from now. You don't know where you are or how much time has passed. You have access to modern astronomical data and technology ...
87 views

### Does Earth's movement around the sun contribute to the angular distance between the moon and planets?

This merged image shows the angular distance between the moon and Mars at 10 PM (upper part) and the change in the angular distance at 10 PM the following day (lower part). My understanding is that ...
3k views

### How do planetarium apps and software calculate positions?

In the most general terms (I'm not asking for the actual calculations), how do popular planetarium apps and software calculate the positions of celestial objects? Planets, for example. Do they use ...
1 vote
65 views

### Mathematical condition of Stationary Planet

In an old astronomy book I find the following definitions: $\vec r_1$ Position vector of Earth (heliocentric) $\vec r_2$ Position vector of a Planet (heliocentric) $\vec v_1$ Velocity vector of Earth (...
76 views

### Mismatch between the equation of the equinoxes and the correction for a right ascension

I am studying about apparent and mean positions of Sun using quite old books: Astronomical algorithms (1991) and Explanatory supplement to the astronomical almanac (1992). The question is about the ...
1 vote
58 views

### moving light with a fading pulse, very bizarre

October 9th southeast of Denver about 6 miles, looking northwest in the sky approximately 10 inches to the left of Alkaid, a bright light, what at first glance might have been a star, began moving ...
128 views

### Positional astronomy - Speed of the sun in sky

Let $\vec{r}$ be the position of the Sun in the sky, from Earth. How could I estimate the magnitude of $d\vec{r}/dt$, to measure the rate of change in time of the arc it traces? I suppose it would be ...
105 views

### Tropical or sidereal orbital period when calculation Solar System positions?

I'm reading Practical Astronomy With Your Calculator Or Spreadsheet by Duffett-Smith and Zwart. When calculating the positions (in equatorial coordinates) of the Sun and planets the authors use the ...
1 vote
103 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 ...
99 views

### How can I compute the shape and orientation of the crescent for a given time and geographic location using data from the JPL Horizons?

I can compute the following data for the Moon for a given time and geographic location using the JPL Horizons system: Apparent RA & DEC Apparent azimuth & elevation (AZ-EL) Target range & ...
147 views

### Measurement unit of coordinate systems in astronomy

Nearly all of the coordinate system I have studied in Positional astronomy use the degree system. This makes me curious about why astronomers prefer degrees over radians as we know that Radian is a ...
936 views

### How was the First Point of Aries measured in ancient times?

According to Wikipedia, usage of the Sun's position as the basis for a celestial coordinate system dates back at least to Babylonian times, and the current "First Point of Aries" system ...
1 vote
63 views

### How to calculate shooting distance for an astronomical object

With a 50mm full frame lens and a 35mm sensor (or film), how far should I be to shoot Earth with earth’s edge just inside top and bottom edge of the resulting image? I don't want any cropping. Earth ...
2k views

### JPL Horizons - "highly accurate measurements of planetary positions" - how do they do it?

According to JPL Horizons, with regard to their planetary position calculations, ... we integrate the equations of motion in Cartesian coordinates ($x,y,z$), and we adjust the initial conditions in ...
123 views

### How can you derive equations between the Horizontal and Equatorial system if the two systems have different centers?

This might be a dumb question. If the center of the celestial sphere is the center of the earth, and the center of the horizontal system is the observer, why do people use this diagram to derive ...
33 views

### LSR and peculiar motion corrections to RAVE survey velocities

I am working towards getting a bunch of halo stars in our galaxy for my thesis. I am doing this with the help of a Toomre diagram and I am stuck. I am using the RAVE survey in conjunction with Gaia as ...
479 views

### Calculation of Terrestrial and Universal time scale difference, ΔT

$\Delta$T is defined as the 'measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of atomic time'. I tried to calculate $\Delta$T corresponding to ...
129 views

### Airy's Water Filled Telescope: help required to fully understand the calibration procedure followed

I am reading/studying the instrument description of Airy's Water Filled Telescope (Airy, G. B., "History and Description of the Water Telescope of the Royal Observatory, Greenwich", ...
1k views

### Compute Distance Between Stars

If I have the following information about star A and Star B, how can I compute the distance between A and B? Distance from Sol for Star A Right Ascension/Declination of Star A Parallax/Absolute ...
112 views

### Small Angle Approximation Discrepancy in Horizon Dip Angle

Let's get back to the classic astronomical problem of calculating horizontal dip angle using small angle approximations. Let, our observer is a point object situated at an height $h$ on the earth ...
260 views

### How to determine sidereal time just looking at the picture?

I have this picture: I need to determine what sidereal time it is (in hours), or how long has it been since the upper culmination of the point of the vernal equinox. How can I do that?
95 views

### Knowing location, LST, the amount & direction of displacement of an unknown star in a 2d image over time, can you calculate the coords of this star?

Basically I have camera, my location, my local sidereal time. I want to point the camera in one direction and shoot a timelapse of a certain star exactly in the middle of the camera view. So I know ...
357 views

### Rising and setting time of planets in relation to the sun

If Venus set about 2 hours after the Sun,then it should be about 30degrees to the east of Sun. Is there any mathematical formula to get these thing or it's just a pattern? Source :https://olympiads....
497 views

### Tips of Crescent

Can it be shown mathematically that the line connecting tips of crescent is parallel to the North-South line and the line gives latitude of the plane ( When the Moon is sufficiently close to the ...
1 vote
194 views

### Angle of Declination and Culminations

Is it true that angle subtended by the Zenith Distance at Upper and Lower culminations is equal to the declination of the star ?If It's true then why? Is the motion of Earth make the solid angle of ...
2k views

### What is the connection between declination and latitude?

The celestial equator is a projection of the terrestrial equator on the celestial sphere. So doesn't that mean the geographical latitude and the declination will be "exactly" equal, as they ...
372 views

### Mathematics for Conversion between ICRS and AltAz

I am writing some software, for my own learning experience, to convert astronomical coordinates to different frames of reference. An example of this would be conversion between ICRS which a lot of ...
111 views

### predicting angular seperation between planetary objects and earth satellites

I am struggling to calculate the angular separation between a satellite in earth orbit and a planetary object using the Skyfield library. It's equivalent to calculating the angular separation between ...
1 vote
712 views

### Altitude of Polaris is latitude

How to prove geometrically that the altitude of Polaris is equal to the latitude? I have seen in handouts that the altitude of the pole star gives the latitude of that place.
71 views

### Rising time of a planet or a star and its correlation with the angle subtended at the Earth

While preparing for Astronomy Olympiad I came across many problems in which we had to calculate at what time a planet or a star would rise at the Earth, and to solve this many solutions found the ...
2k views

### Calculating the position of stars at a given point in time

Is there any particular methods that help us calculate the position of a star at a certain point in time? This question is what I am trying to achieve, but for me, I do not want to use the data ...