How an enormous project attempted to map the sky without computers:
Recently, the European Space Agency released the third installment of data from the Gaia satellite, a public catalog that provides the positions and velocities of over a billion stars. This is our most recent attempt to answer some of the most long-standing questions in astronomy: How are stars (and nebulae) spread out across the sky? How many of them are there, how far away are they, and how bright are they? Do they change in position or brightness? Are there new classes of objects that are unknown to science?
For centuries, astronomers have tried to answer these questions, and that work has been laborious and time-consuming. It wasn't always easy to record what you could see in your telescope lens—if you were lucky enough to have a telescope at all.
Now imagine the emergence of a new technique that, for its time, offered some of the benefits of the technology that enabled the Gaia catalogs. It could automatically and impartially record what you see, and anyone could use it.
That technique was photography.
This article tells the story of how photography changed astronomy and how hundreds of astronomers formed the first international scientific collaboration to create the Carte du Ciel (literally, "Map of the Sky"), a complete photographic survey of the sky. That collaboration resulted in a century-long struggle to process thousands of photographic plates taken over decades, with the positions of millions of stars measured by hand to make the largest catalog of the night sky.
(Score: 5, Interesting) by bzipitidoo on Friday September 16 2022, @04:14PM (5 children)
I took a look at some Gaia data, to try to determine if Planet 9 could be detected with the wobble method. My back of the envelope calculations show it might barely be possible. Very precise measurements of the nearest stars could show us wobbling with respect to them.
The barycenter of the Sun/Planet 9 system, presuming a Planet 9 that is at the closer and less massive end of the estimated ranges, is still outside the sun. One Earth year's worth of wobble looks to be too little for Gaia to detect, but 2 years, maybe it could pick that up. If that is possible, then the Gaia data could give us a direction. All we have now is a range of possible orbits, with no way to find out where in its orbit Planet 9 might be right now.
I did learn that Gaia data is corrected for the known planets. So, yes, the gas giants do wobble the sun enough for Gaia to detect. Planet 9 is so far away that even though it could be only 5 Earth masses, its great distance more than makes up for it smaller mass. It wobbles the sun farther than any other planet. The problem is, of course that it is an exceedingly slow wobble.
(Score: 2) by takyon on Friday September 16 2022, @10:22PM (2 children)
https://www.inverse.com/science/planet-nine-vera-rubin-telescope [inverse.com]
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(Score: 2) by bzipitidoo on Sunday September 18 2022, @11:25PM (1 child)
Only have to wait 2 more years? Positively an eyeblink on astronomical time scales! 2024 is shaping up to be a fun year for astronomy. The upcoming eclipse of April 8, 2024 will pass right over my home.
I have not studied astronomy in any depth, and have only picked up facts here and there. I used not to know, for instance, that orbits gradually become less eccentric over time thanks to, as I recall, tidal forces, and, when Sedna was found, was puzzled that its orbit was described as weird. I put the high eccentricity down to its great distance from the sun, thinking, well, why shouldn't such distant objects have rather more varied orbits? Thought close encounters with other solar systems could explain it.
I daresay though, that astronomers will still try to find Planet 9 sooner, if they can. Won't wait for Vera Rubin. Too huge a feather in the cap to be the one or the team that bags Planet 9 first.
(Score: 2) by takyon on Monday September 19 2022, @02:52AM
The main Planet Nine crew: Brown + Batygin, Sheppard + Trujillo, have been using the Subaru Telescope to systematically search for it. But it is a slow search that gets impeded when one of their observation days is hit by bad weather.
Maybe LSST could find Planet Nine in a very short amount of time. If it would be fast as DAY ONE due to being obvious, I wonder if it can happen before the official first light in 2024 as they are testing it:
It has been delayed by years, a real tragedy, and there is doomingsaying about Starlink's effects on the survey.
Even if it doesn't find Planet Nine, the huge amount of TNOs it finds should be useful to Planet Nine's proponents or opponents. One theory is that collective gravity [colorado.edu] explains observed orbits. Increase the number of known objects by 1-2 orders of magnitude, including more objects with eccentric orbits, and you have a lot more data points to work with.
Yes, it's likely that visits by other stars coming as close as 0.1 to 1 light year have perturbed the orbits:
https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs#Distant_future_and_past_encounters [wikipedia.org]
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(Score: 1) by khallow on Saturday September 17 2022, @12:28AM (1 child)
[...]
The first observation is important. It takes on the order of a small multiple of the period of the orbit to detect the wobble. For a hypothetical planet 9, this could be on the order of thousands to millions of years.
I would suspect a better strategy would be to measure perturbations of existing known objects which have much shorter orbital periods, and then look for star scintillation in suspected regions. The gravitational field of a planet 9 would distort the light of any stars/galaxies it passes in front of even if it doesn't exactly intersect the light source.
(Score: 2) by hubie on Sunday September 18 2022, @03:04PM
I think the GR deflection from Jupiter is on the order of a micro-arcsecond max, but the Gaia catalog is only good to positions of something like a milli-arcsecond (star dependent), so looking for any GR lensing would be very challenging.