Questions tagged [celestial-mechanics]

Questions regarding the motions of celestial objects.

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What causes the short term variation in the length of a march-equinox year

By a "march-equinox year" I mean the time between successive march/vernal equinoxes. I understand that this is different from the mean tropical year, and I also understand why this would be ...
anonymous's user avatar
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Is the Moon really oscillating around its orbit as seen from Earth?

While simulating today's eclipse, I see something I have never noticed or learnt: Stellarium shows an oscillation of the Moon's trajectory around its orbit as seen from Earth. Is it real or a ...
Cingonius Varro's user avatar
8 votes
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Would be possible to detect Planet Nine as a microlensing event along the line of its projected orbit?

Theoretically proposed by Konstantin Batygin and Mike Brown (@Caltech), Planet Nine could have a mass of $\sim 6.3 \pm 2 M_{\oplus}$. Even though I don't know if the hypothesis is still feasible at ...
nuwe's user avatar
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How is the amount and direction of the Sun's axial tilt as observed from other planets calculated?

Not long ago I asked this question; turns out that was fairly simple to figure out given the equatorial coordinates of the Sun's north pole (just convert to ecliptic coordinates, and see when the Sun ...
Outis Nemo's user avatar
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Why do these two sources list different values for the Solar axial tilt to the ecliptic and Earth's orbital inclination to the Solar equator?

On the Wikipedia article for axial tilt the Solar axial tilt is listed as 7.25° to the ecliptic, whereas on the Wikipedia article of orbital inclination Earth is listed as having an orbital ...
Outis Nemo's user avatar
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Looking for data and models for events of Sun and Moon apparent motion in distant past?

For the current Julian Era (from 1, 1, 4713 BCE to modern day), I am looking for a raw data tables or a model that allows to predict the following events related to apparent motion of Sun and Moon: ...
Suiinditor Impudens's user avatar
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Hierarchy of gravitational interactions of astronomical objects: from single to large-scale structures

Hierarchical structure is clearly visible in the Universe. The "observable universe" includes almost empty voids, between which lie large cosmic filaments. The filaments consist of galactic ...
dtn's user avatar
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How to convert TEME (or ITRF) to horizontal

I have TEME coordinates from sgp4 propagation. I can convert those (in python) to ITRF given date and time of observation. How to convert coordinates from one of those two frames to horizontal azimuth ...
jlipinski's user avatar
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Will all satellites get inevitably tidally locked to their planet?

Are there cases or conditions in which an object orbiting another one (e.g. a satellite and its planet) does not get tidally locked to it? For example, in this question, it is mentioned that a large ...
vengaq's user avatar
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What is the difference between SPICE kernels and JPL Development Ephemerides? Is a DE just a bunch of kernels on a string?

My imposter syndrome is acting up again after I posted several comments under: What is the mathematics needed for understanding DE440 and translating it into xyz coordinates? Now I feel like I don't ...
uhoh's user avatar
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What is the mathematics needed for understanding DE440 and translating it into xyz coordinates?

I would like to write my own code to process NASA's DE440/DE441 ephemerides, but I do not know the mathematics needed to do this. I understand packages such as pyephem have implemented variations of ...
Ana's user avatar
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Code for Gauss's method orbit determination

I'm trying to calculate the state vectors of the ISS using Gauss's method with three sets of values (right ascension, declination and sidereal time). I'm following the method described in "...
specimen_n1l3's user avatar
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Do all the planets travel along the same constellations?

If humans ever moved to another planet in this solar-system, what constellations would the sun meet from that perspective? What constellations would the sun look like it is meeting from the ...
Atlas's user avatar
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largest balanced mass objects in Earth's L4 & L5 Lagrange points?

What is the largest single-object mass that would allow two objects of equal mass to have a stable orbit, one each, in Earth's L4 and L5 Lagrange points?
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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 ...
McAllister's user avatar
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How is Earth's Rotation Angle (ERA) defined and measured

UTC typically ticks with TAI. But to keep UTC from drifting far from the rotation angle of the Earth we occasionally add leap seconds to ensure that UTC does not drift too far from the UT1 timescale. ...
Jagerber48's user avatar
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How to find zero velocity contours for circular restricted 3-body problem in x-y plane?

(I am having physics background; I am not an astronomer/astrophysicist.) How to solve a single nonlinear algebraic equation in two variables, $x$ and $y$? (I know that - if there are two variables, ...
atom's user avatar
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Do the inner-Earth planets actually align with the constellations we see?

For example, because the Sun is the center of the solar system; when we think that the Sun is on the constellation of Aries, in actuality, isn't Earth lining up with the constellation opposite Aries: ...
Atlas's user avatar
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Different techniques for calculation of celestial bodies dynamics with different time-scales

Differential equations describing the dynamics of celestial bodies (rotation, nutation, precession and other effects) can be solved numerically, which makes it possible to study their general non-...
dtn's user avatar
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What stars are brighter then any star nearer to the south celestial pole [closed]

What stars are brighter (apparent magnitude) then any star nearer to the south celestial pole? I know that there’s no bright star within a few degrees of the south celestial pole.
blademan9999's user avatar
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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 ...
KidAtticus's user avatar
1 vote
1 answer
175 views

What is the horizon-ecliptic angle formula?

For an observer in a city with latitude 35°, at what sidereal time is the angle that the ecliptic makes with the horizon equal to the angle that the equator makes with the horizon? What is the angular ...
Astro enthusiast's user avatar
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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 ...
nuwe's user avatar
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calculating MPC orbital uncertainty parameter U

I'm trying to understand how the orbital uncertainty parameter 'U' introduced by the Minor Planet Center (MPC) is actually calculated for minor bodies. This wikipedia page gives the formulae to be ...
mysterium's user avatar
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Celestial Coordinates and Sun's degrees below horizon

I am struggling to understand the how the coordinates work. Example: At vernal equinox RA=0 DEC=0, Does this mean the Sun is at its highest point at the equator? If my mean solar time is 2h 30min, ...
Niki11's user avatar
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179 views

constant semi-major axes of the planets

in Numerical Expressions for Precession Formulae And Mean Elements for the Moon And the Planets (Simon et al., 1994), the orbital elements of the planets are given for long time durations. The semi-...
theorist's user avatar
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different corresponding coefficients in formulae for a mean element

why do they take λ₁ = 1 295 977 422.834 29ʺ from subsection 5.8.3.¹ (mean elements referred to the mean dynamical ecliptic and equinox J2000), and not λ₁ = 1 296 027 711.034 29ʺ from subsection 5.9.3.¹...
theorist's user avatar
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218 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 ...
ALiCe P.'s user avatar
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Orbital terminology for satellites relative to one another

Basic question, but I'm trying to describe a planetary system and coming up short on vocabulary. Do either of the following exist?: A word for the closest pass between two satellites orbiting the ...
the-baby-is-you's user avatar
25 votes
2 answers
3k views

How can Io be tidally heated while it is in tidal lock?

According to its Wikipedia page: Rotation period: synchronous Eccentricity: 0.0041 But also ...extreme geologic activity is the result of tidal heating... How is it possible? It should not be ...
peterh's user avatar
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6 votes
1 answer
3k views

How to calculate the altitude of a star given the hour angle, declination, and latitude?

I'm trying to find the altitude of a star for observing, but all I have is the hour angle and declination of the star, along with latitude of the location I'm observing from. How can I find the ...
altitudeFinder's user avatar
11 votes
3 answers
2k views

What's the meaning of virial in Astronomy, and in particular the expression "a virialized cluster of galaxies"?

The virial theorem relates the kinetic energy of a system to the total potential energy of the system: $ \Delta K = -\frac{1}{2}\Delta V $ so it has lots of uses in mechanics, thermodynamics and ...
Jim421616's user avatar
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1 vote
1 answer
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Schmidt corrector plate on a Newtonian = Schmidt Cassegrain?

Went on with a wide range of telescopes and its mechanics. To my understanding, the only change in the optical function in Schmidt Cassegrain telescope is a Schmidt's corrector plate in front of an ...
Kavin Ishwaran's user avatar
1 vote
0 answers
100 views

Why is Earth at centre of Celestial Sphere?

Why do we consider Earth to be at the centre for Celestial Sphere ? If so, then how will Sun revolve around Earth ? Doesn't it mean its like the geocentric model ?
Suhas Adiga's user avatar
3 votes
1 answer
114 views

Querying MPC data : P and Q vectors of any use to compute the eccentricity vector?

While querying the Minor Planet Center orbital data for asteroids, among the returned data, I noticed 6 variables corresponding to x,y and z components of two 3-D vectors namely P and Q. The ...
mysterium's user avatar
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3 votes
1 answer
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Can you compute the solar day?

For a given planet, if you know the sidereal rotation period and the sidereal revolution period, can you compute the length of one solar day? For instance, for Earth, if you know one rotation is ...
usernumber's user avatar
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3 votes
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Mars is getting closer to Earth through its elliptical orbit becoming more eccentric. Do Earth and Mars keep getting closer? [closed]

A NASA Mars article says: Mars' orbit is more elliptical than Earth's, so the difference between perihelion and aphelion is greater. Over the past centuries, Mars' orbit has been getting more and ...
Rob Clennell's user avatar
2 votes
0 answers
152 views

Virial theorem for a binary system

I am trying to derive the virial theorem but for two stars orbiting each other. I know the derivation for the general virial theorem with i particles but I am wondering if there is a quicker or more ...
I Love Math's user avatar
7 votes
1 answer
504 views

Degrees of freedom in restricted circular coplanar three body problem

How many degrees of freedom does a mechanical system consisting of three bodies, the Sun, Jupiter and an asteroid, have in the restricted circular coplanar problem of the three bodies? I know that if ...
Augustin's user avatar
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3 votes
2 answers
150 views

Can we learn anything from the chaotic movement of Hydra and Nix?

The NASA Visualization Explorer Moons In Chaos says Hydra and Nix, two of the moons of Pluto, show chaotic movement due to the shifting gravitational field. How long a day lasts and where the sun ...
Bahnhofstrasse's user avatar
2 votes
0 answers
91 views

Orbital resonance 2:1

I considered the motion of an asteroid around the sun, in a $2:1$ orbital resonance with Jupiter. Following the study of this resonance, it was observed that the angle between the major axis of the ...
Augustin's user avatar
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2 votes
1 answer
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Orbital resonance - basic aspects

In the following lines, I will ask you some questions regarding the notion of orbital resonance. I know that the orbital resonance of two celestial body represents the driving of a dynamical system by ...
Augustin's user avatar
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3 votes
1 answer
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Orbital resonances - expansion of disturbing function

I want to study the orbital resonance type 3:1 between an asteroid and Jupiter. For this purpose, I found the expansion of the disturbing function, $R$, in Celletti A., Stability and Chaos in ...
Augustin's user avatar
  • 153
1 vote
1 answer
113 views

Orbital parameters of the Sun [duplicate]

What are the orbital parameters of the Sun such as orbit velocity etc in it's orbit around the Solar System's center of mass? Consider the Sun pointlike or alternatively when talkin about the Sun's ...
Some Student's user avatar
0 votes
0 answers
42 views

Accretion disk formation

Why a mass transfer in a binary star system, from the less dense star to the denser star forms an accretion disk? Why the material does not fall directly to the denserstar?
Niche's user avatar
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0 votes
1 answer
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Trajectory: What would happen if the sun disappeared one day?

So, let's just assume, to no aspect explainable to humans, the sun just magically popped out of existence on January 1st next year (2022), that'll never happen, this is just a scenario to explain my ...
Questioner's user avatar
9 votes
2 answers
2k views

Spotting the booster rocket of the Chinese space station?

SpaceWeather.com's newsletter states Sky watchers are reporting two new objects in the night sky: China's new space station and an out-of-control booster rocket that helped launch it. The tumbling ...
B--rian's user avatar
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5 votes
1 answer
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Coordinates in the Night Sky

I've learned about Orbits recently, and there are 6 orbital elements. Now, I've heard of three coordinate systems whereas, they can help you measure positions of stars in the night sky. The Altazimuth,...
Questioner's user avatar
3 votes
1 answer
68 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?
magnolia1's user avatar
1 vote
1 answer
392 views

Keplerian Elements

So, I've been doing endless research, and I've found a bit of information, all in different places, that is. Now, I'm getting really confused about it; I can't keep up with it all anymore, so, now, it'...
Questioner's user avatar