Talk:Orbital period

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Changed 'a' back to kilometers (see below). Checked this against: Wertz and Larson, Space Mission Analysis and Design (SMAD) 3rd ed. Table 6-2, pp 137.

R.A Barnes Undergraduate Satellite Engineer

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i made a change below to meters instead of km in semi major axis because the formula does not give the correct answer if you input "a" in kms.

Small body orbiting a central body

In astrodynamics the orbital period (in seconds) of a small body orbiting a central body in a circular or elliptical orbit is:

...

and

(standard gravitational parameter)

where:

is length of orbit's semi-major axis (km),

David C.S Ong —Preceding unsigned comment added by 134.115.68.21 (talk) 09:58, 28 September 2007 (UTC)

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Whispers from the land of ignorants ...

This is a great article (Orbital Period page). I don't quite understand one section, however. The point under the 2-bodies-orbiting section: "... the sum of the semi-major axes of the ellipses in which the centers of the bodies move, or equivalently, the semi-major axis of the ellipse in which one body moves, in the frame of reference with the other body at the origin (which is equal to their constant separation for circular orbits) ..."

To use this in the calculation for determining the orbital period -- would I just sum the semi-major axes for both ellipses? E.g. two stars orbiting each other: "Star A" has a semi-major axis of 100 AU, and a mass of 1.5 Solar Masses. "Star B" has a semi-major axis of 300 AU, and a mass of 0.25 Solar Masses. Would I use 400 AU in the formula?

Thanks, Tesseract501(August 27, 2005)

Mass and semi-major axis are inversely proportional, so the example does not seem possible, but yes, we just add the semi-major axes.--Patrick 00:03, 28 August 2005 (UTC)

You'd use the total distance, 100+300 AU, and the total mass, 1.50+0.25 M_Sun.

Urhixidur 15:35, 14 December 2005 (UTC)

Letter P and letter T are both used in this article to signify orbital period. Which one should be preferred ? Bo Jacoby 10:32, 14 December 2005 (UTC)

I would say T, like Frequency uses.--Patrick 14:05, 14 December 2005 (UTC)

Diagram

It would be nice to see some diagrams showing the difference between the orbital periods. —Preceding unsigned comment added by Reddwarf2956 (talk • contribs) 09:53, 23 September 2009

Going backwards

This whole effort seems to be going in the wrong direction. To take only one example, the reference to the tropical year (as of 01:49, 12 September 2008) was well written and coherent. The current version (as of 10:19 UTC 14 November 2009) of the same topic is illiterate goobledegook. I hesitate to make an edit since it appears to be a waste of time. —Preceding unsigned comment added by 64.180.221.68 (talk)

Small body orbiting a central body Error

The formula provided states that T is in seconds, but the units in the formula work out that the result is seconds squared, not seconds. It's fundamentally wrong.

Unfortunately, I haven't found another reference to replace it from yet... —Preceding unsigned comment added by 67.164.83.84 (talk) 01:37, 18 November 2009 (UTC)

The formula is correct. The units of the gravitational constant G are m³/(kg•s²). The units of a³ are canceled by m³, while the units of M₁ + M₂ are canceled by kg. This leaves s², which the square root sign reduces to seconds. — Joe Kress (talk) 09:54, 18 November 2009 (UTC)

Ah, yes. I was checking with wolfram, and had parens wrong. Thanks for the correction. —Preceding unsigned comment added by 128.170.62.95 (talk) 17:33, 18 November 2009 (UTC)

Units of measure

This article contains several mathematical equations relating various physical quantities. Only one of these equations specifies any units of measure. It is good style and certainly a favor to the reader if all the units of physical quantities are specified explicitly. When such a specification is absent the results are meaningless. For example, the equation: T = 3.3 \sqrt{(a/R)^3} clearly results from some choice of units for T, a and R (and also implicitly for the constant value 3.3). We are told that T is in hours, but what are the units of a and R? Meters, miles, inches, astronomical units? I could do the calculations to answer that question myself but I feel that people should do their own homework, otherwise they won't learn. — Preceding unsigned comment added by 154.5.32.113 (talk) 09:45, 30 May 2011 (UTC)

This sentence is gibberish.

"It differs from the sidereal period because the node is a coinciding of planes rather than a linear coinciding, and the object's line of nodes typically precesses or recesses slowly in relation to orbital cycle."

Two coincident planes really constitute a single plane. I think the author of this sentence means to say that the line of nodes is the line of intersection of the plane of the orbit and the plane of the ecliptic. (I don't know what he means by a "linear coinciding.") And it is true that as the plane of the ecliptic precesses this line of nodes rotates about the normal to the orbit. Therefore any period measured with respect to this direction will also change over time.154.5.45.119 (talk) 23:25, 30 August 2011 (UTC)

"Citation needed" for orbiting body of water

Under section 2.2 (Orbital period as a function of central body's density), the editor provided the equation for calculating the orbital period of a body around another given the density of the second body. He then proceeded to illustrate a possible use of the equation by showing the result of the calculation if the body orbiting the earth were made of water. For some reason, that example has been flagged, [citation needed]. Could someone elaborate on that? Julesmazur (talk) 19:28, 12 February 2013 (UTC)

synodic period and gravity

It seems like there should be some comment about gravitation peaks and valleys in respect to the synodic period that elapses between two successive conjunctions with the Star–planet_1 line in the same linear order. Maybe even something with how this relates to orbital stability and orbital resonance. John W. Nicholson (talk) 11:36, 2 March 2013 (UTC)