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Indian astronomers
The following was just inserted into the History section:
Ancient astronomers like Aryabhatta II , bhaskara had done preliminary study and come up with fairly accurate orbits and forward orbital interpolations .
I have moved it here because there is no source. Also, the capitalization of the name(s) seems wrong, and it was just stuck into the history section without any meaningful discussion of the role of Indian astronomers in the area of secular variations of planetary orbits. --Gerry Ashton (talk) 20:40, 25 February 2008 (UTC)
Stable orbit
The following talk was in the discussion page of Kepler's laws of planetary motion. But an anonymous user suggested that this page is more appropriate for the talk :
According to Kepler's third law, the period of a planetary motion is propotional to the 3/2 th power of radius ( or semi major axis. ) But this is an idealised case. In reality, there is a very diffuse gas in the Solar system and the motion of the planets around Sun may be retarded by this gas. To be sure, the retarding effect is negligable. But the cumulative effect over millions of years may be considerable, which means that the delicate balance between the gravitational and cetrifugal forces is in danger. But luckily, we haven't observed any spirally inward motion of any planet. I think that the article must have a section to explain how the planets maintain their orbits over billions of years. Nedim Ardoğa (talk) 16:11, 16 October 2009 (UTC)
- Maybe there should be a section, but it would have to be based on reliable sources, not speculation. --Jc3s5h (talk) 16:30, 16 October 2009 (UTC)
- I have read several papers which discuss the evolution of planetary orbits and none have ever considered any diffuse gas retarding the planets. They have considered solar mass loss due to solar luminosity and solar wind, but this has increased Earth's orbital radius by the negligible amount of only the diameter of Earth over the last 4.5 billion years. See [1].
- But the planets do not "maintain their orbits over billions of years". They don't even maintain their orbits over thousands of years because the planets perturb each others' orbits. Their orbits move in inertial space in essentially three ways: the line of their apsides (perihelion-aphelion) rotate, their inclinations to the invariable plane of the solar system change, and their eccentricities change. These changes are slow enough to allow any single orbit to be considered an ellipse, but even a few orbits produce noticeable changes in their "elliptical" orbits. Nevertheless, Newton's universal theory of gravitation coupled with mathematical techniques developed by Euler and others (embodied by VSOP over a few thousand years) can be used to calculate these orbits for at least several million years (if computational capacity was available). But many small bodies that orbit the Sun cannot complete even a single orbit without a significant deviation from an ellipse.
- Only the four jovian planets (Jupiter, Saturn, Uranus, and Neptune) have orbits that can be rigorously calculated over the 10-billion year life of the solar system. The orbits of the terrestrial planets (Mars, Earth, Venus, and Mercury) are chaotic beyond about 30 million years. Venus and Earth are moderately chaotic, whereas Mars and especially Mercury are wildly chaotic. The eccentricity of Mercury can reach 0.9, causing its orbit to intersect that of Venus, possibly resulting in a collision. Furthermore, resonance with Jupiter can cause the entire inner solar system to destabilize about 3.3 billion years from now (1% probability), possibly resulting in the ejection of Mercury or Mars from the solar system, the collision of Mercury with the Sun, or the collision of any two of these four planets. See Mercury, Mars, Venus and the Earth: when worlds collide!. A good overview is Stability of the solar system. The red giant Sun will engulf Mercury, Venus and Earth (if they still survive) in 7.6 billion years. See Distant future of the Sun and Earth revisited. — Joe Kress (talk) 08:21, 17 October 2009 (UTC)
I would like to thank Joe Kress for his informative talk. (I will follow the links he suggested.) But I am afraid, such topics as effects of heavenly bodies on each other and future red giant stage of Sun are not exactly what I'd like see in this article. I merely ask for a paragraph which explains how the planets manage to maintain the stability of their orbits in the presence of interstellar gas. (By the way for the presence of diffuse gas see Solar System (Interplanetary medium) and Interstellar medium ) Nedim Ardoğa (talk) 13:52, 18 October 2009 (UTC)
- Interplanetary medium discusses the solar wind and interplanetary dust. In addition, much larger meteoroids continually bombard all planets, preferentially on the side facing the direction of their orbital motion. But again, I've never seen any one consider these effects on the evolution of planetary orbits, so even discussing maintaining planetary orbits in their presence can only be discussed in the article if you can find a reliable source. — Joe Kress (talk) 23:02, 18 October 2009 (UTC)
- I instead propose Kepler's laws of planetary motion for that topic. Rursus dixit. (mbork3!) 21:01, 14 March 2010 (UTC)
Dubious paragraph
The second paragraph of History seems to be in grave grave error: it currently claims that Tycho, Kepler and Newton couldn't make predictions on their work, but instead extrapolated earlier observations. Seems like contrafactual to me, the real story going about as following:
- Copernicus made a full heliocentric system based on epicycles, including computations and predictions, which however was better than the geocentric system based on Ptolemy and updated medieval tables of Toledo, only because the medieval tables of Toledo weren't fresh, and Copernicus'es tables were fresh;
- Kepler was the first to introduce elliptical orbits, among others using the very computational Kepler's Equation which together with spherical trigonometry and orbital elements of the planets — computed by Kepler himself — is quite enough to compute planetary orbits better than any epicycle-based system;
- Newton made so much maths and physics, up to and including founding mathematical analysis, so that one could derive Kepler's Equation from his classical general theory of gravity, and also parabolic and hyperbolic motion with unprecedented precision; it was with this maths that Halley connected a number of comet occurrences to be one comet, later named Halley's Comet after him. This feat he performed already in 1705.
Rursus dixit. (mbork3!) 21:01, 14 March 2010 (UTC)
- The gist of that paragraph is from a VSOP article IIRC. "Higher mathematics" refers to the first solutions of the multibody problem (three or more bodies) by Leonard Euler, Tobias Mayer and other mathematicians about 1750. Newton was unable, using only his gravitational theory, to find the position of the Moon, which is a three-body problem, Moon-Earth-Sun. Elliptical orbits for planets and predicting the orbit of a comet like Halley are both two-body problems. — Joe Kress (talk) 07:07, 20 March 2010 (UTC)
Expanding spacetime theory
I'm not a cosmologist so I can't give a professional judgement, but this theory smells of fringe science. The article cowritten by Kolesnik & Masreliez looks legit on superficial inspection, but predates the self-published (?) book and seems to have no clear relation to it. Unless reliable sources can be found that demonstrate that 1) Masreliez's expanding spacetime theory is mainstream science and 2) this is relevant to the current article the links do not belong in this article. Martijn Meijering (talk) 10:10, 20 May 2010 (UTC)
- Hi Martijn,
- How come you don't like the smell? Maybe you are just mixing fringe science up with pseudo science? As for the predating, I do not get your point. Kolesnik published his first ideas on the secular accelerations in 1995/-96, which Masreliez is referring to in his first (1999) peer reviewed paper on his SEC model and his popular book account (2000), as one possible evidence of his predicted new drag effect. Kolesnik finalized his analysis of planetary data and had it published with Masreliez in 2004.
- Before crying for mainstream perhaps you should take a look at non-standard cosmology. The outcome should have a bearing on ephemeris up-datings. Cheers / Kurtan (talk) 13:57, 21 May 2010 (UTC)
- Looks dodgy to me, too William M. Connolley (talk) 19:38, 9 February 2011 (UTC)
I've moved this to talk for now, since I don't trust it.
Planetary secular acceleration of cosmological origin
Traditionally, the secular bias in residuals of differential optical observations of the Sun and planets results from the following four factors:
- constant error in the proper motions of a reference catalog (residual rotation with respect to the dynamical reference frame);
- the effect of the tidal acceleration of Earth;
- secular errors of the longitudes in a comparison ephemeris;
- systematic observation errors.
Masreliez cosmological model SEC of (1999), being a conformal time FLRW solution of Einstein's field equations of general relativity, predicts an alternative explanation that planets secular acceleration is also of cosmological origin. The net result is that the planet accelerates in its orbit, while slowly falling toward the sun. The relation for the change in angular velocity given by SEC is
where 1/ is the Hubble time and ω is the increasing angular velocity. This tiny change will cause the Earth to fall roughly 22 meters closer to the Sun per year.
About 240,000 worldwide optical observations of the Sun, Mercury, and Venus, accumulated during the entire era of classical astrometry from James Bradley up to the present, were compiled by Kolesnik et al during the 1990s and used to analyze the secular longitude variations of the innermost planets. A reduction method relating historical planetary observations to the Hipparcos reference frame is presented. Secular trends in the longitudes of the Sun, Mercury, and Venus with respect to the ephemeris DE405 are estimated for the time span 1750-2000.[1] It was concluded that
the apparent equinox motion resulting from the 250 year interval of optical observations cannot be interpreted as an actual rotation of the Hipparcos system. More likely, it is caused by systematic errors in the right ascensions of the 19th century observations. In order to properly investigate the residual rotation of a reference catalog, only 20th century observations should be used.
Discussion of the above
(note that the above is a version *after* a few mods I made. See [2] for the "original").
This section relies heavily on the Masreliez model, yet that link is to a family name not a person. So a bare minimum for re-insertion has to be identifying the author of this theory William M. Connolley (talk) 13:06, 10 February 2011 (UTC)
- No more, he is now on the family article. If you understand French (I don't), you can follow the links to a person article there. I did a short version on the Japanese wp some time ago, as I find his ideas quite viable. Mariguld (talk) 15:41, 27 February 2011 (UTC)
- The Masreliez model, Expanding Spacetime Theory, beeing a non-standard cosmology inviting disputes, you should not expect to find it, or a person article, on all wp versions. So if this prank is for reaching some kind of consensus, I suggest the passage be reinstated without delay. Mr Gearloose (talk) 12:20, 9 March 2011 (UTC)
Arbab / Intro
The intro ends
- Lesser secular accelerations of cosmological origin in the solar system have been verified by Arbab (2008)[1]. Arbab is relying on an additional theory that emerged 1999-2004 from compiling planetary observations by Russian astronomer Yuri B. Kolesnik and theoretical predictions in a cosmological context by Swedish-American physicist C. Johan Masreliez.[2]
But there is no mention of Arbab in the article. This needs to be resolved, by either deleting him from the intro or adding to the article William M. Connolley (talk) 14:59, 11 March 2011 (UTC)
- Which article is supposed to mention Arbab? If I recall correctly, Arbab (2008) is citing Masreliez (2004) and I take it that's why the additional, missing fact was added. If you are going to have a substantial chunk of "secular accelerations of cosmological origin" in the article, as I too claim you should, it must certainly be mentioned in the intro. Stop making a mess of this once quite informative article. Kurtan (talk) 20:01, 11 March 2011 (UTC)