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Earth's orbit
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The Earth at different points in its orbit
Earth's orbit is the trajectory along which Earth travels around the Sun. The average distance between the Earth and the Sun is 149.60 million km (92.96 million mi),[1] and one complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi).[2] Earth's orbit has an eccentricity of 0.0167.
As seen from Earth, the planet's orbital prograde motion makes the Sun appear to move with respect to other stars at a rate of about 1° (or a Sun or Moon diameter every 12 hours) eastward per solar day.[nb 1] Earth's orbital speed averages about 30 km/s (108,000 km/h; 67,000 mph), which is fast enough to cover the planet's diameter in 7 minutes and the distance to the Moon in 4 hours.[3]
From a vantage point above the north pole of either the Sun or Earth, Earth would appear to revolve in a counterclockwise direction around the Sun. From the same vantage point, both the Earth and the Sun would appear to rotate also in a counterclockwise direction about their respective axes.
Contents
[hide]
1 History of study
2 Influence on Earth
3 Events in the orbit
4 Future
5 See also
6 Notes
7 References
8 External links
History of study[edit]
Main article: Heliocentrism
Heliocentric Solar System
Heliocentrism (lower panel) in comparison to the geocentric model (upper panel)
Heliocentrism is the scientific model that first placed the Sun at the center of the Solar System and put the planets, including Earth, in its orbit. Historically, heliocentrism is opposed to geocentrism, which placed the Earth at the center. Aristarchus of Samos already proposed a heliocentric model in the 3rd century BC. In the 16th century, Nicolaus Copernicus' De revolutionibus presented a full discussion of a heliocentric model of the universe[4] in much the same way as Ptolemy had presented his geocentric model in the 2nd century. This "Copernican revolution" resolved the issue of planetary retrograde motion by arguing that such motion was only perceived and apparent. "Although Copernicus's groundbreaking book...had been [printed] over a century earlier, [the Dutch mapmaker] Joan Blaeu was the first mapmaker to incorporate his revolutionary heliocentric theory into a map of the world."[5]
Influence on Earth[edit]
Main article: Season
Because of Earth's axial tilt (often known as the obliquity of the ecliptic), the inclination of the Sun's trajectory in the sky (as seen by an observer on Earth's surface) varies over the course of the year. For an observer at a northern latitude, when the north pole is tilted toward the Sun the day lasts longer and the Sun appears higher in the sky. This results in warmer average temperatures, as additional solar radiation reaches the surface. When the north pole is tilted away from the Sun, the reverse is true and the weather is generally cooler. Above the Arctic Circle and below the Antarctic Circle, an extreme case is reached in which there is no sunlight at all for part of the year. This is called a polar night. This variation in the weather (because of the direction of the Earth's axial tilt) results in the seasons.[6]
Events in the orbit[edit]
By astronomical convention, the four seasons are determined by the solstices – the two points in the Earth's orbit of the maximum tilt of the Earth's axis, towards the Sun or away from the Sun – and the equinoxes – the two points in the Earth's orbit where the Earth's tilted axis and an imaginary line drawn from the Earth to the Sun are exactly perpendicular to one another. The solstices and equinoxes divide the year up into four approximately equal parts. In the northern hemisphere winter solstice occurs on or about December 21; summer solstice is near June 21; spring equinox is around March 20; and autumnal equinox is about September 23.[7] The effect of the Earth's axial tilt in the southern hemisphere is the opposite of that in the northern hemisphere, thus the seasons of the solstices and equinoxes in the southern hemisphere are the reverse of those in the northern hemisphere (e.g. the northern summer solstice is at the same time as the southern winter solstice).
In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4 (for other eras, see precession and Milankovitch cycles). The changing Earth–Sun distance results in an increase of about 6.9%[8] in total solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere.[9]
The Hill sphere (gravitational sphere of influence) of the Earth is about 1,500,000 kilometers (0.01 AU) in radius, or approximately 4 times the average distance to the moon.[10][nb 2] This is the maximal distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects orbiting the Earth must be within this radius, otherwise they can become unbound by the gravitational perturbation of the Sun.
Orbital characteristics
epoch J2000.0[nb 3]
aphelion 152.10×10^6 km (94.51×10^6 mi)
1.0167 AU[nb 4]
perihelion 147.10×10^6 km (91.40×10^6 mi)
0.98329 AU[nb 4]
semimajor axis 149.60×10^6 km (92.96×10^6 mi)
1.000001018 AU[11]
eccentricity 0.0167086[11]
inclination 7.155° to Sun's equator
1.578690°[12] to invariable plane
longitude of the ascending node 174.9°[11]
longitude of perihelion 102.9°[11]
argument of periapsis 288.1°[11][nb 5]
period 365.256363004 days[13]
average speed 29.78 km/s (18.50 mi/s)[3]
107,200 km/h (66,600 mph)
The following diagram shows the relation between the line of solstice and the line of apsides of Earth's elliptical orbit. The orbital ellipse goes through each of the six Earth images, which are sequentially the perihelion (periapsis — nearest point to the Sun) on anywhere from January 2 to January 5, the point of March equinox on March 19, 20, or 21, the point of June solstice on June 20, 21, or 22, the aphelion (apoapsis — farthest point from the Sun) on anywhere from July 3 to July 5, the September equinox on September 22, 23, or 24, and the December solstice on December 21, 22, or 23.[7] The diagram shows an exaggerated shape of Earth's orbit; the actual orbit is less eccentric than pictured.
Because of the axial tilt of the Earth in its orbit, the maximal intensity of Sun rays hits the Earth 23.4 degrees north of equator at the June Solstice (at the Tropic of Cancer), and 23.4 degrees south of equator at the December Solstice (at the Tropic of Capricorn).[14]
Future[edit]
Main article: Stability of the Solar System
Mathematicians and astronomers (such as Laplace, Lagrange, Gauss, Poincaré, Kolmogorov, Vladimir Arnold, and Jürgen Moser) have searched for evidence for the stability of the planetary motions, and this quest led to many mathematical developments and several successive "proofs" of stability for the Solar System.[15] By most predictions, Earth's orbit will be relatively stable over long periods.[16]
In 1989, Jacques Laskar's work indicated that the Earth's orbit (as well as the orbits of all the inner planets) can become chaotic and that an error as small as 15 meters in measuring the initial position of the Earth today would make it impossible to predict where the Earth would be in its orbit in just over 100 million years' time.[17] Modeling the Solar System is a subject covered by the n-body problem.
See also[edit]
Astronomy portal
Astronomical unit
Barycenter
Earth's axial tilt
Earth's rotation
Geocentric orbit – the orbit of any object orbiting the Earth, such as the Moon or an artificial satellite
Satellite
Space station
Notes[edit]
Jump up ^ Our planet takes about 365 days to orbit the Sun. A full orbit has 360°. That fact demonstrates that each day, the Earth travels roughly 1° in its orbit. Thus, the Sun will appear to move eastward across the sky relative to the stars by that same amount.
Jump up ^ For the Earth, the Hill radius is
R H = a ( m 3 M ) 1 / 3 , {\displaystyle R_{H}=a\left({\frac {m}{3M}}\right)^{1/3},}
where m is the mass of the Earth, a is an astronomical unit, and M is the mass of the Sun. So the radius in AU is about ( 1 3 ⋅ 332 946 ) 1 / 3 ≈ 0.01 {\displaystyle \left({\frac {1}{3\cdot 332\,946}}\right)^{1/3}\approx 0.01} .[citation needed]
Jump up ^ All astronomical quantities vary, both secularly and periodically. The quantities given are the values at the instant J2000.0 of the secular variation, ignoring all periodic variations.
^ Jump up to: a b aphelion = a × (1 + e); perihelion = a × (1 – e), where a is the semi-major axis and e is the eccentricity.
Jump up ^ The reference lists the longitude of perihelion, which is the sum of the longitude of the ascending node and the argument of perihelion. Subtracting from that (102.937°) the node longitude of 174.873° gives −71.936°. Adding 360° gives 288.064°. That addition does not change the angle but expresses it in the usual 0–360° range for longitudes.
References[edit]
Jump up ^ "Sun: Facts & Figures". Solar System Exploration. National Aeronautics and Space Administration. Retrieved July 29, 2015.
Jump up ^ Jean Meeus, Astronomical Algorithms 2nd ed, ISBN 0-943396-61-1 (Richmond, VA: Willmann-Bell, 1998) 238. See Ellipse#Circumference. The formula by Ramanujan is accurate enough.
^ Jump up to: a b Williams, David R. (2004-09-01). "Earth Fact Sheet". NASA. Retrieved 2007-03-17.
Jump up ^ De revolutionibus orbium coelestium. Johannes Petreius. 1543.
Jump up ^ Jerry Brotton, A History of the World in Twelve Maps, London: Allen Lane, 2012, ISBN 9781846140990 p. 262.
Jump up ^ "What causes the seasons? (NASA)". Retrieved January 22, 2015.
^ Jump up to: a b "Date & Time of Solstices & Equinoxes". August 28, 2013. Retrieved Jan 22, 2015.
Jump up ^ Aphelion is 103.4% of the distance to perihelion. See "Orbital characteristics" table. Due to the inverse square law, the radiation at perihelion is about 106.9% of the radiation at aphelion.[citation needed]
Jump up ^ Williams, Jack (2005-12-20). "Earth's tilt creates seasons". USAToday. Retrieved 2007-03-17.
Jump up ^ Vázquez, M.; Montañés Rodríguez, P.; Palle, E. (2006). "The Earth as an Object of Astrophysical Interest in the Search for Extrasolar Planets" (PDF). Instituto de Astrofísica de Canarias. Retrieved 2007-03-21.
^ Jump up to: a b c d e Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–683. Bibcode:1994A&A...282..663S.
Jump up ^ Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 294. ISBN 0-387-98746-0.
Jump up ^ The figure appears in multiple references, and is derived from the VSOP87 elements from section 5.8.3, p. 675 of the following: Simon, J. L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–683. Bibcode:1994A&A...282..663S.
Jump up ^ "What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle?". Retrieved Jan 22, 2015.
Jump up ^ Laskar, J. (2001). "Solar System: Stability". In Murdin, Paul. Encyclopedia of Astronomy and Astropvhysics. Bristol: Institute of Physics Publishing. article 2198. [permanent dead link]
Jump up ^ Gribbin, John (2004). Deep simplicity : bringing order to chaos and complexity (1st U.S. ed.). New York: Random House. ISBN 978-1-4000-6256-0.
Jump up ^ "Earth-Venus smash-up possible". June 11, 2009. Retrieved Jan 22, 2015.
External links[edit]
Media related to Earth's orbit at Wikimedia Commons
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text:
Talk:Tennis ball
From Wikipedia, the free encyclopedia
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Contents
[hide]
1 old unsigned
2 Ball Color
3 Numbers on balls
4 Manufacturing
5 Environmental issues related to tennis balls
6 Hairy Balls?
7 Vandalism?
8 Pressureless Ball section is a mess
9 Spongebob balls
old unsigned[edit]
I am curious about the date that tennis balls went from being white to being fluourescent yellow. I understand that this change was to enhance visibility, and that there have been experiments (none that have succeeded commercially, I believe) with other colors or combinations of colors. As a child I watched the U.S. Open at the Westside Tennis Club in Forest Hills, N.Y. The balls were white (that would be in the 50's), and it was a prize to get a ball inadvertently hit into the stands with it's distinctive green stain from the grass surface. For years the U.S. Open has been played at the National Tennis Center in Flushing Meadows, N.Y. where the hard surface gives the players more reliable bounces and the balls, of course, are fluourescent yellow.
Just so everyone knows, that's totally my tennis ball - Nick
Ball Color[edit]
Historically, balls were either black or white in colour, depending on the background colour of the courts. In 1972 the ITF introduced yellow tennis balls into the rules of tennis, as research had shown these balls to be more visible to television viewers. Meanwhile Wimbledon continued to use the traditional white ball, but eventually adopted yellow balls in 1986. ref= http://www.itftennis.com/technical/equipment/balls/history.asp HUH HI hi HI hi HI hi HI hi
Just an interesting note: I have polled about 300 people about the color of the classic tennis ball, even showing many of them a picture, and it's split 50-50 as to whether it's green or yellow. Clearly its green. --JohnLattier 00:45, 1 November 2006 (UTC)
How can anyone think the ball color is yellow? Can anyone actually look at the picture on the Tennis Ball page and tell me it's yellow with a straight face. What's next the recycling symbol is yellow? (Actually more yellow than Tennis Ball but it is even considered green). For the record I just arbitrarily changed it from yellow to green, then I get a message saying I gave false information. Then I stumbled upon this, and I'm happy to see people agreeing with me. Either 1. Find a picture of an incorrect yellow tennis Ball or 2. Do the obvious and admit the picture shown is green. By the way, who decides this? I thought wikipedia was open to change! Then (suddenly) I'm under the fear that I won't be able to make changes, because some admin thinks it's yellow. Doesn't this match the definition of fascism or will that be changed now too? —Preceding unsigned comment added by 68.36.66.188 (talk) 02:45, 28 June 2008 (UTC)
Regardless of what historically is the classic color of a tennis ball, the article says, "Modern tennis balls are generally made in a fluorescent yellow color like the ball pictured above (called "optic yellow")." The ball pictured above is green. Surely they don't call that color "optic yellow", do they? —Preceding unsigned comment added by Albedoa (talk • contribs) 15:13, 28 May 2008 (UTC)
Tennis balls are generally a bright yellow, but they do seem to have a slight greenish tinge. I believe the image on the page looks extraordinarily green because of unnatural lighting conditions in the photo. Someone is welcome to produce a more clear image... Freedomlinux (talk) 01:23, 20 June 2008 (UTC)
Unnatural lighting? That is the weakest excuse for denying facts. Here is a link to a correctly colored tennis ball picture. I have seen the yellow tennis balls people are referring to only once. This is not the correct color of a tennis ball, and I would be willing to pay someone if they could show me a tennis ball that looks like this.
The first picture you link to shows a color of tennis ball I have never seen. Go to the store, folks, and look at a can of brand new tennis balls. You'll see that they are nothing like this odd ball and much closer to this. Some even say "optic yellow" on the can. As the balls get used, the color dulls, and it's my theory that since most are played on a surface that is painted green, the balls pick up some of that green color. In any case, there is a very slight green tint to new tennis balls that somehow is enhanced as the balls are used. See this image for an example. Matches10 (talk) 03:52, 26 July 2008 (UTC)
Numbers on balls[edit]
Anybody know what those numbers on the balls mean?
I always thought it was simply to tell them apart from tennis balls used by those on adjacent courts.. -EdGl 21:43, 14 April 2006 (UTC)
The number on the tennis ball is used to tell them apart, so is the brand name, this is a go=;56kbne
This is correct. The number on the ball is simply to help you know which are yours and help prevent mixups. The idea that the numbers stand for anything physical about the ball is absurd. If there were any physical difference between tennis balls of the same brand that were numbered differently, the manufacturer would certainly do a better job of telling the purchaser what the difference is. Tennis ball cans don't state clearly what number is on the balls in the can, and the cans are all together on the shelves. Balls with "1" can be found in the same row as balls with "3" and "2", etc.
It's the number of times you need to bounce it before you serve. --OhNoPeedyPeebles 19:34, 30 August 2007 (UTC)

It's to do with the properties of the ball- I think higher numbers are bouncier, but I can't remember exactly. —Preceding unsigned comment added by 86.21.224.201 (talk) 18:08, 9 December 2007 (UTC)
Low level players should use lower numbered balls (ie. 1 or 2), number 3 and above are more for intermediate-pro players. higher numbered balls up to 10 can be obtained from high-level grounds (sometimes available in shops and mob drops). 05 January 2008 - AsteroidS™

I've always thought they are to tell them apart from tennis balls used by those on adjacent courts. However, I have opened a can which had multiple numbers in it. This defeats the entire purpose of the reason. — Preceding unsigned comment added by 110.20.53.163 (talk) 13:38, 22 September 2014 (UTC)
Yes the numbers on the balls are simply to identify them as your court's (in high school I once served off the side of my racket at a tournament and it flew through six adjacent courts so it helps). The stuff about higher bounce is an internet invention. I can't imagine the cost additions to ball production if they took each individual ball, measured the internal pressure to within a fraction of an atmosphere (or better yet, took the the time to measure the height of a "bounce test" haha), separated and stamped them accordingly, and then packaged them in multiple separate lines. Also, the previous comment about getting multiple numbers in the same can seems questionable to me. Was it a new (unopened) can? I've been playing tennis for 25 years and there has never been such an occurrence. It would defeat the (actual) purpose of the numbering. Username4761 (talk) 00:54, 15 February 2015 (UTC)
Manufacturing[edit]
Could we perhaps add a segment on how they are produced? 155.92.33.244 22:40, 29 October 2007 (UTC)
Is there any particular reason why we are told the ball is of the same size and shape as a baseball? I don't know how big a baseball is and have never come across one in my life.
Anyone could explain how to fill air inside the pressurized tennis ball? as far as I know, there are 2 methods, chemical and physical, but not in detail. please help...thanks in advance! — Preceding unsigned comment added by 203.116.198.71 (talk) 08:45, 28 November 2012 (UTC)

As far as I can tell, the chemical method means a pellet is inserted between the two halves of the ball. The two halves are sealed together and the pellet vaporises into a gas which creates pressure. The little rattle heard inside a ball sometimes is a pellet which didn't fully vaporise.
The physical method is the two halves are joined inside a pressurised chamber so the ball retains that pressure when it is sealed. — Preceding unsigned comment added by 110.20.53.163 (talk) 13:52, 22 September 2014 (UTC)
Environmental issues related to tennis balls[edit]
Chairs with tennis balls
Text was added as noted below:
by Soundgreen (Talk | contribs) at 18:23, 26 April 2008
"Each year approximately 300 million balls are produced, which contributes roughly 32.3 million pounds of waste. Historically, tennis ball recycling has not existed and the most common use has been to cut the ball into two semi-spheres and attach this to the bottom of chairs in schools, nursing homes and the like."
(Is that truly the most common use? Has this been verified? I'd have thought the most common reuse of tennis balls was as dog toys, and I've seen far more split tennis balls as trailer hitch covers than as chair feet Jbrecken (talk) 21:05, 2 June 2008 (UTC)Jbrecken) Well, from what we have researched, the most common is to poke a hole in them and put them on the bottom of chairs/rockers. Even #s wise, we haven't found any "data" but there are only so many dog parks, etc. Most pros said they donate to schools, nursing homes, etc, while a few mentioned they donate to an animal shelter or dog park. I can site our research and interviews, but I doubt that is what you would likeSoundgreen (talk) 19:17, 29 August 2008 (UTC)
I'm very interested in knowing more about waste issues related to: 1) Their being shipped in bulk in separate plastic vacuum sealed cans, 2) Their not being able to be reinflated, which results in their being thrown out when they no longer bounce well, 3) Any manufacturers that market decent tennis balls that are not preinflated and are, rather, inflated (and later reinflated) by the consumer, 4) Anything else.
So, if Soundgren, or others, can tell me where the currently cited info came from and/or where I might look to learn more.

Thanks! --Bkengland (talk) 16:56, 1 May 2008 (UTC)
The guy was linkspamming his recycling company on the article so it probably comes from his firm. Montco (talk) 02:49, 2 May 2008 (UTC)
Oh well! Still, I'd sure be interested in finding some solid information and stats on this, and then maybe that could be used, in part, in this article.--Bkengland (talk) 17:27, 2 May 2008 (UTC)
Montco - it isn't linkspamming if the company is legitimately a tennis ball manufacturer, which we are. So kindly allow the link to survive. Bkengland - re: your questions
1 - not sure how to quantify the shipping. The vast majority (>90%) are made in SE Asia due to the raw material input (rubber). They are then boat shipped to where ever. No ball manufacturer sells direct to consumer, rather they only ship to distributors who then ship to pro shops, stores, etc.
2 - there is only one viable, proven recharge technique... Rebounces, LLC holds the proprietary knowledge and has built a business around this technology. We have not had one pro disapprove of our recharged balls, nor have we found anyone who has another alternative method that works in bulk
3A- there are "pressurless" balls i.e. balls that aren't built in traditional manner, however there are several issues with these balls - different weight than approved balls (which is 2 ounces), the ball bounces differently, players say the balls feel "heavy on their strings", the balls wear out (i.e. lose pressure) around 90 days. Companies include Tretorn, Gamma, Dunlop and Penn. 3B - Rebounces.com is the only company that sells "reinflated" balls in bulk
4 - Rebounces.com cannot solve the initial shipping problem, however we have purchased Carbon Offsets for each of our shipments. Again, we are the only company that can reinflate a ball in bulk. The balls have the same bounce, feel, etc. They wear out the same - approximately 10-14 days after our process. We can reuse the same ball multiple times (4+) depending on the felt quality of the ball.
Cheers Soundgreen (talk) 19:17, 29 August 2008 (UTC)
Hairy Balls?[edit]
"This human hair is believed to have come from the enemies of the Scottish, and was harvested on one of their many conquests to Great Britain." Who are these enemies conquering Great Britain - the English? How did their balls get stuck in the roof? It's one to ponder. --OhNoPeedyPeebles (talk) 18:10, 23 October 2008 (UTC)
I have removed that sentence, its very dubious, and a little work revealed that it was added by a seemingly tennis ball obsessed vandal. Midlandstoday (talk) 23:20, 25 December 2008 (UTC)
Vandalism?[edit]
One section says "History of yo mama. This is vandalism, right? --72.136.31.208 (talk) 23:42, 6 January 2009 (UTC)
Pressureless Ball section is a mess[edit]
The narrative provided in the pressureless ball section is incoherent (to me). I recommend revision to cut out seemingly irrelevant and/or unsubstantiated information. — Preceding unsigned comment added by DotSlashSteven (talk • contribs) 00:21, 14 May 2012 (UTC)
Spongebob balls[edit]
Classic case of Citogenesis. Google can only find two mentions of this, both are blog posts from after the content was inserted a while ago by an IP. I can't believe no one found and challenged this for four years!!!—Love, Kelvinsong talk 18:38, 5 September 2013 (UTC)
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