I Measuring the Velocities of Astronomical Objects in the Milky Way

[Al-Layth]

I am looking for the most relied upon studies that measured the motions of the sun, earth, jupiter...etc any or all of the various astronomical objects in the milky way galaxy. Particularly interested in the orbital velocities of the planets

 

[Drakkith]

That's a good question and I don't have an answer to it. However, I did facebook message the IAU about tracking solar system objects and updating our model with their positions and velocities. I'll post their response if they get back to me.

 

[Baluncore]

Particularly interested in the orbital velocities of the planets

Reliable with reference to what ?
Everything is moving, orbiting a wandering barycenter, referenced to an equinox, that drifts.
https://en.wikipedia.org/wiki/Celestial_mechanics

There are software packages that do a good job of predicting the positions of astronomical objects.
https://en.wikipedia.org/wiki/Numerical_model_of_the_Solar_System
https://en.wikipedia.org/wiki/VSOP_model

 

[pinball1970]

.... all of the various astronomical objects in the milky way galaxy.

That is a lot of objects! Assuming you do mean Milky way and not just solar system, there are some maps on the web.

The link below is 2019 so pre JWST, I will be surprised if teams like the ones who have put this map together have not booked some hours in with Webb.
https://www.space.com/milky-way-3d-map-warped-shape.html

One obvious thing about the map that is not explained is that it only shows a few stars on one side. That is because it is difficult to see the other side of the galaxy due to the amount of dust and objects between our line of site and the other side. (Webb will come in useful here)
Also note the use of classical Cepheid stars as standard candles.

https://en.m.wikipedia.org/wiki/Classical_Cepheid_variable

I will not attempt to expand on overall motions.
https://phys.org/news/2010-11-milky..., including our own,the form of density waves.

 

[russ_watters]

There are software packages that do a good job of predicting the positions of astronomical objects.
https://en.wikipedia.org/wiki/Numerical_model_of_the_Solar_System
https://en.wikipedia.org/wiki/VSOP_model

I think OP is asking where the input data for the model comes from. Famously, the first quality database of astronomical position observations was Tycho Brahe's (though, where'd the makers of Stonehenge get theirs?). Is there a gold standard today, that such software packages are based on? And/or, the math isn't super complicated: are the models publicly available, with starting points that are refined over time?

 

[Baluncore]

Google 'SLALIB'
SLALIB — Positional Astronomy Library - Starlink
Astrophysics Source Code Library
https://ascl.net/1403.025

 

[russ_watters]

I am looking for the most relied upon studies that measured the motions of the sun, earth, jupiter...etc any or all of the various astronomical objects in the milky way galaxy. Particularly interested in the orbital velocities of the planets

Velocity isn't a measured input, it's an output. A stable orbit has only one possible velocity for each location on the orbit, which can be calculated, if you want - it isn't needed for an orbit model. Measuring a handful of points enables the shape of the orbit to be traced, and then derived mathematically (eccentricity, inclination).

 

[Baluncore]

I think, rather than expressing general interest in perfection, the OP needs to specify the task at hand.

The positions of the planets and our moon are computed from polynomial approximations of coefficients with hundreds of terms, that are good for thousands of years, BC to AD. Nothing has a simple fixed period, everything is changing and evolving.

Google to find huge positional databases of different objects.

The SLALIB Starlink Introduction to Celestial Mechanics.
http://star-www.rl.ac.uk/docs/sun67.htx/sun67.html\

There are a few good introductions for beginners by Jean Meeus that predate SLALIB and the Starlink project.
Google; Astronomical algorithms.
Astronomical formulae for calculators.
https://archive.org/details/astronomicalalgorithmsjeanmeeus1991

 

[Astronuc]

sun, earth, jupiter..

all of the various astronomical objects in the milky way galaxy.

The solar system and milky way galaxy are to very different orders of scale. The planetary movements around the sun are well known of which Russ gave an example, and there are many more astronomers since. The galaxy is orders of magnitude more complicated given the billions of stars, dust clouds, nebula, the dense core, and objects on the other side of the dense core. Nevertheless, there are plenty of galactic maps of stars and objects, and velocities of those objects based on years of observation.

NASA/Caltech run a simulator of the solar system - real tiime.
https://solarsystem.nasa.gov/resources/2515/real-time-real-data/
https://sites.astro.caltech.edu/~dperley/programs/ssms.html

Major planets would be included, but small objects in the asteroid belt, Kuiper Belt and Oort Cloud may not be, or some may be approximated.

ESA’s Gaia mission has produced the richest star catalogue to date, including high-precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our home Galaxy.

https://www.esa.int/Science_Explora...tes_richest_star_map_of_our_Galaxy_and_beyond

NASA is mapping the Milky Way Galaxy. I would expect that NASA and ESA are sharing data with numerous universities and observatories.
https://www.nasa.gov/jpl/charting-the-milky-way-from-the-inside-out

Gaia Data Release 2 - Mapping the Milky Way disc kinematics (2018)
https://www.aanda.org/articles/aa/full_html/2018/08/aa32865-18/aa32865-18.html

Deep Star Map 2020
https://svs.gsfc.nasa.gov/4851

 

[ETERNITY Starship]

Ref orbital velocities of planets in our solar system

The speeds constantly change due to subtle interactions with other planets and other non planetary mass

We have yet to map all the mass in the solar system ... no mass map = no accurate speed map

Lots of work is ongoing and accuracy is very slowly improving

Current orbital speed accuracy in 2023 is +/- 1% (most peer reviewed figures will be in this error range)

For project / mission specific speeds accuracy can often be calculated to 1 part in a thousand*Most space probes need to make course corrections en route ... this is a reflection of the current level of accuracy of orbital predictions and a reflection in variations of rocket thrust.

** There are 101 small factors that throw off the accuracy of calculations.

*** Thus when trying to predict the orbit of ANY object there are LIMITS to accuracy ... its akin to trying to predicting the weather on Earth ... Not all 'factors' are known, of those that are known the value and influence of those known factors is often not well understood.

 

[Vanadium 50]

We have yet to map all the mass in the solar system ... no mass map = no accurate speed map

I don't believe that can be right. 1% in velocity is 2% of the mass. That's ten earth mass. More if they are far away.

I can believe velocities vary that much because of orbital eccentricity (be surprised if they didn't). I can believe there are 10 Earth masses of unknown stuff way out beyond Neptune where it makes little difference. But I don;t believe there is enough undiscovered mass to cause a 1% change.

To set the scale, if a planet's velocity changed by 1% after completing an orbit, the orbit wouldn't close. The object would only last between 100-10000 orbits (depending on the details) before being ejected. For Mercury, that's 2400 years, tops. But we have records that it has been around even longer.

 

[Baluncore]

Ref orbital velocities of planets in our solar system

The speeds constantly change due to subtle interactions with other planets and other non planetary mass

The future positions do not need to be predicted from first principles with precision model parameters. A model requires integration steps, that will amplify the errors exponentially and catastrophically.

Planetary position is very accurately predicted by software that fits polynomials of order hundreds, to long term historical observational data.
https://en.wikipedia.org/wiki/Starlink_Project

Those polynomials could be inverted to obtain the mass and position parameters for a lump model, but then we would just get back to accumulating the errors of numerical integration.

Following departure from Earth, the velocity of a spacecraft can be measured to more than six digits accuracy by using the Doppler shift of digital ranging codes returning from the spacecraft transponder.
https://en.wikipedia.org/wiki/Gold_code

Once the on-board optical navigational instruments observe the next target, fine corrections can be made that are referenced towards the destination, not referenced from the Earth.