Earth's orbit
As seen from Earth, the planet's orbital
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.
History of study
Influence on Earth
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. North of the Arctic Circle and south of the Antarctic Circle, an extreme case is reached in which there is no daylight at all for part of the year, and continuous daylight during the opposite time of year. This is called polar night and midnight sun, respectively. This variation in the weather (because of the direction of the Earth's axial tilt) results in the seasons.[6]
Events in the orbit
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, toward 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
The
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) 1.0000010178 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 orbital speed | 29.78 km/s (18.50 mi/s)[3] 107,208 km/h (66,616 mph) |
speed at aphelion | 29.29 km/s (18.20 mi/s)[3] |
speed at perihelion | 30.29 km/s (18.82 mi/s)[3] |
The following diagram illustrates the positions and relationship between the lines of solstices, equinoxes, and apsides of Earth's elliptical orbit. The six Earth images are positions along the orbital ellipse, 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—the 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]
Future
Mathematicians and astronomers (such as
In 1989, Jacques Laskar's work indicated that 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 Earth would be in its orbit in just over 100 million years' time.[16] Modeling the Solar System is a subject covered by the n-body problem.
See also
Notes
- ^ 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 across the sky relative to the stars by that same amount.
- ^ For the Earth, the Hill radius is
- J2000.0of the secular variation, ignoring all periodic variations.
- ^ a b aphelion = a × (1 + e); perihelion = a × (1 – e), where a is the semi-major axis and e is the eccentricity.
- 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
- National Aeronautics and Space Administration. Archived from the originalon July 3, 2015. Retrieved July 29, 2015.
- ISBN 0-943396-61-1 (Richmond, VA: Willmann-Bell, 1998) 238. See Ellipse#Circumference. The formula by Ramanujan is accurate enough.[citation needed]
- ^ a b c d Williams, David R. (1 September 2004). "Earth Fact Sheet". NASA. Retrieved 17 March 2007.
- ^ De revolutionibus orbium coelestium. Johannes Petreius. 1543.
- ISBN 9781846140990p. 262.
- ^ "What causes the seasons? (NASA)". Retrieved 22 January 2015.
- ^ a b "Date & Time of Solstices & Equinoxes". 28 August 2013. Retrieved 22 January 2015.
- ^ "Solar Energy Reaching The Earth's Surface". ITACA. Archived from the original on 30 January 2022. Retrieved 30 January 2022.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - ^ Williams, Jack (20 December 2005). "Earth's tilt creates seasons". USAToday. Retrieved 17 March 2007.
- ^ 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 21 March 2007.
- ^ Bibcode:1994A&A...282..663S.
- ISBN 0-387-98746-0.
- Bibcode:1994A&A...282..663S.
- Institute of Physics Publishing. article 2198.
- ISBN 978-1-4000-6256-0.
- ^ "Earth-Venus smash-up possible". 11 June 2009. Archived from the original on 23 January 2015. Retrieved 22 January 2015.