3753 Cruithne

Discovery
Discovered by:	Duncan Waldron
Discovery date:	October 10, 1986
Orbital characteristics
Epoch July 14, 2004 (JD 2453200.5)
Aphelion distance:	226.105 Gm (1.511 AU)
Perihelion distance:	72.415 Gm (0.484 AU)
Semi-major axis:	149.260 Gm (0.998 AU)
Eccentricity:	0.515
Orbital period:	364.019 d (1.00 a)
Avg. orbital speed:	27.73 km/s
Mean anomaly:	190.171°
Inclination:	19.810°
Longitude of ascending node:	126.311°
Argument of perihelion:	43.719°
Physical characteristics
Dimensions:	~5 km
Mass:	1.3×1014 kg
Mean density:	2 ? g/cm³
Equatorial surface gravity:	0.0014 m/s²
Escape velocity:	0.0026 km/s
Rotation period:	? d
Albedo:	0.15 ?
Temperature:	~275 K
Spectral type:	?
Absolute magnitude:	15.1

3753 Cruithne (pronounced /ˈkrɪnjə/, Modern Irish /ˈkrɪhnʲə/) is an asteroid in orbit around the Sun. Due to its unusual orbit relative to that of the Earth, it is a periodic inclusion planetoid. It is sometimes called "Earth's second moon",^[1] although it is not a satellite of the Earth. by 0. ... J. Duncan Waldron is an astronomer, artist, and furniture designer. ... is the 283rd day of the year (284th in leap years) in the Gregorian calendar. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... The Julian day or Julian day number (JDN) is the integer number of days that have elapsed since the initial epoch defined as noon Universal Time (UT) Monday, January 1, 4713 BC in the proleptic Julian calendar [1]. That noon-to-noon day is counted as Julian day 0. ... A diagram of Keplerian orbital elements. ... A diagram of Keplerian orbital elements. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... Look up giga- in Wiktionary, the free dictionary. ... ‹ The template below (Unit of length) is being considered for deletion. ... The astronomical unit (AU or au or a. ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Look up day in Wiktionary, the free dictionary. ... In astronomy, a Julian year is a unit of time defined as exactly 365. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... Kilo (symbol: k) is a prefix in the SI system denoting 103 or 1000. ... Look up second in Wiktionary, the free dictionary. ... In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. ... Inclination in general is the angle between a reference plane and another plane or axis of direction. ... This article describes the unit of angle. ... The Longitude of the ascending node (☊, also noted Ω) is one of the orbital elements used to specify the orbit of an object in space. ... The argument of periapsis (ω) is the orbital element describing the angle between an orbiting bodys ascending node (the point where the body crosses the plane of reference from South to North) and its periapsis (the point of closest approach to the central body), measured in the orbital plane and... This article or section is in need of attention from an expert on the subject. ... The kilogram or kilogramme (symbol: kg) is the SI base unit of mass. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Centi (symbol c) is a SI prefix in the SI system of units denoting a factor of 10-2, or 1/100. ... The cubic meter (symbol m³) is the SI derived unit of volume. ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Space Shuttle Atlantis launches on mission STS-71. ... In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis relative to the background stars. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ... Fig. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... Articles with similar titles include the NATO phonetic alphabet, which has also informally been called the “International Phonetic Alphabet”. For information on how to read IPA transcriptions of English words, see IPA chart for English. ... 253 Mathilde, a C-type asteroid. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... Sol redirects here. ... This article is about Earth as a planet. ... Look up Planetoid in Wiktionary, the free dictionary. ... This article is about Earths moon. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ...

Discovery

Cruithne was discovered on October 10, 1986, by Duncan Waldron on a photographic plate taken with the UK Schmidt Telescope at Siding Spring Observatory, Coonabarabran, Australia. The 1983 apparition (1983 UH) is credited to Giovanni de Sanctis and Richard M. West of the European Southern Observatory in Chile. It was not until 1997 that its unusual orbit was determined by Paul Wiegert and Kimmo Innanen, working at York University in Toronto, and Seppo Mikkola, working at the University of Turku in Finland. is the 283rd day of the year (284th in leap years) in the Gregorian calendar. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ... J. Duncan Waldron is an astronomer, artist, and furniture designer. ... The 1. ... The Anglo-Australian Telescope at Siding Spring Observatory Siding Spring Observatory near Coonabarabran, Australia, part of the Research School of Astronomy & Astrophysics (RSAA) at the Australian National University (ANU), incorporates the Anglo-Australian Telescope along with a collection of other telescopes owned by the Australian National University, the University of... Coonabarabran, a town in northern New South Wales, Australia, has about 3000 inhabitants and was established in the 1850s. ... Giovanni de Sanctis is an Italian astronomer at the Astronomical Observatory of Turin in Turin, Italy. ... Richard Martin West (born 1941) is a Danish astronomer working at the European Southern Observatory (ESO). ... The European Southern Observatory (ESO) is an international astronomical organisation, composed and supported by ten countries from the European Union plus Switzerland. ... York University (French: Université York), located in Toronto, Ontario, is Canadas third-largest university and has produced several of the countrys top leaders in the fields of law, politics, business, space sciences, and fine arts. ... The University of Turku (Finnish Turun yliopisto, Swedish Åbo universitet), located in Turku in southwestern Finland, is the second largest university in the country as measured by student enrolment. ...

The asteroid is named after the Cruithne people (also known as the Priteni or the Picts) who inhabited Scotland and parts of Ireland between 800 BCE and 1000 CE; the name may specifically refer to their legendary first leader, also called Cruithne. For the asteroid, see 3753 Cruithne. ... For the asteroid sometimes (incorrectly) identified as Earths second moon, see 3753 Cruithne. ... A replica of the Hilton of Cadboll Stone. ... This article is about the country. ... (9th century BC - 8th century BC - 7th century BC - other centuries) (800s BC - 790s BC - 780s BC - 770s BC - 760s BC - 750s BC - 740s BC - 730s BC - 720s BC - 710s BC - 700s BC - other decades) (2nd millennium BC - 1st millennium BC - 1st millennium AD) Events Golden age in Armenia Assyria... Europe in 1000 The year 1000 of the Gregorian Calendar was the last year of the 10th century as well as the last year of the first millennium. ...

Dimensions and orbit

Cruithne is approximately 5 km in diameter, and its closest approach to Earth is approximately 30 times the separation between Earth and the Moon (12 Gm or million kilometres). Although Cruithne's orbit is not thought to be stable over the long term, calculations by Wiegert and Innanen showed that it has likely been in sync with Earth's orbit for a long time. There is no danger of a collision with Earth for millions of years, if ever. Cruithne is not visible to the naked eye at any point in its orbit. To help compare different orders of magnitude this page lists lengths between 10 and 100 km (104 to 105 m). ... ‹ The template below (Unit of length) is being considered for deletion. ... DIAMETER is a computer networking protocol for AAA (Authentication, Authorization and Accounting). ... This article is about Earths moon. ... To help compare different distances this page lists lengths starting at 1010 metres (10 million kilometres, 0. ... Onomastics and disambiguational information about the words and place & human names that forms Wieg, Wiege-. die Wiege (di vig) means cradle. ...

Cruithne is in a normal elliptic orbit around the Sun. However, because its period of revolution around the Sun is almost exactly equal to that of the Earth, they appear to "follow" each other in their paths around the Sun. This is why Cruithe is sometimes called "Earth's second moon".^[2] Cruithne's distance from the Sun and orbital speed vary a lot more than the Earth's, so from our point of view Cruithne actually follows a kidney bean-shaped horseshoe orbit ahead of the Earth, taking slightly less than one year to complete a circuit of the "bean". Because it takes slightly less than a year, the Earth "falls behind" the bean a little more each year, and so from our point of view, the circuit is not quite closed, but rather like a spiral loop that moves slowly away from the Earth. Two bodies with similar mass orbiting around a common barycenter with elliptic orbits. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Dry kidney beans The kidney bean is a medium-sized variety of the common bean (Phaseolus vulgaris) with dark red skin. ... A horseshoe orbit is the type of orbit you get when you observe an object from another nearly co-orbital object, such as a planet. ...

After many years, the Earth has fallen behind far enough that Cruithne is now actually "catching up" on the Earth from "behind". When it eventually does catch up, Cruithne will make a series of annual close approaches to the Earth, and gravitationally exchange orbital energy with Earth; this will alter Cruithne's orbit by a little over half a million kilometres (whilst Earth's orbit is altered by about 1.3 centimetres) so that its period of revolution around the Sun is now slightly more than a year. The kidney bean now starts to migrate away from the Earth again in the opposite direction — instead of the Earth "falling behind" the bean, the Earth is now "pulling away from" the bean. The next such series of close approaches will be centred around the year 2292 — in July of that year, Cruithne will approach Earth to about 12.5 million km. In orbital mechanics and aerospace engineering, a gravitational slingshot or gravity assist is the use of the gravity of a planet or other celestial body to alter the path and speed of a spacecraft. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... To help compare different distances this page lists lengths starting at 1010 metres (10 million kilometres, 0. ...

After 380 to 390 years or so, the kidney-bean-shaped orbit approaches Earth again from the other side, and the Earth, once more, alters the orbit of Cruithne so that its period of revolution around the Sun is again slightly less than a year (this last happened with a series of close approaches centred on 1902, and will next happen with a series centered on 2676). The pattern then repeats itself.

Similar minor planets

Three other near-Earth asteroids (NEAs), (54509) 2000 PH₅, (85770) 1998 UP₁ and 2002 AA₂₉, which exist in resonant orbits similar to Cruithne's, have since been discovered. Asteroid 2002 AA29 (also written 2002 AA29) is a near-Earth asteroid discovered in January 2001 by the LINEAR asteroid survey. ...

Other examples of natural bodies known to be in horseshoe orbits include Janus and Epimetheus, natural satellites of Saturn. The orbits these two moons follow around Saturn are much simpler than the one Cruithne follows, but operate along the same general principles. A horseshoe orbit is the type of orbit you get when you observe an object from another nearly co-orbital object, such as a planet. ... Janus (jay-nus, Greek Ιανός) is a moon of Saturn. ... Epimetheus (ep-i-mee-thee-us, Greek Επιμηθεύς) is a moon of Saturn. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...

Mars has one known co-orbital asteroid (5261 Eureka), and Jupiter has many (more than 1000 known objects, the Trojan asteroids); there are also other small co-orbital moons in the Saturnian system: Telesto and Calypso with Tethys, and Helene and Polydeuces with Dione. However, none of these follow horseshoe orbits. Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... 5261 Eureka was discovered at Mt Palomar on June 20, 1990 and turned out to be the first known Mars Trojan asteroid. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Image of the Trojan asteroids in front of and behind Jupiter along its orbital path. ... Atmosphere none Telesto IPA: , Greek Τελεστώ) is a moon of Saturn. ... Atmosphere none Calypso (ka-lip-soe, Greek Καλυψώ) is a moon of Saturn. ... Atmosphere none Tethys (tee-thəs or teth-əs, IPA , Greek Τηθύς) is a moon of Saturn that was discovered by Giovanni Domenico Cassini in 1684. ... Helene (hel-e-nee, Greek ‘Ελένη) is a moon of Saturn. ... Saturns moon Polydeuces Atmosphere none Polydeuces (pol-ee-dew-seez, IPA: , Greek Πολυδεύκης) is a very small natural satellite of Saturn that is co-orbital with Dione and librates around the trailing Lagrangian point (L5). ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ...

See also

• Co-orbital moon
• Lilith, Earth's hypothetical "dark moon"
• Natural satellite
• Quasi-satellite
• Cruithne in fiction
• 6R10DB9

Co-orbital moons are natural satellites that orbit at the same distance from their parent planet as another satellite, or at a similar distance. ... Lilith is a hypothetical natural satellite of Earth. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Diagram of generic quasi-satellite orbit A quasi-satellite is an object similar to a planet or satellite of the Sun, however its orbit encompasses its planet and the planets star. ... Asteroids have become a common theme in science fiction. ... 6R10DB9 is a small asteroid, with a diameter of about one meter, temporarily orbiting the Earth, with a period of about three months. ...

External links

• Paul Wiegert's page about Cruithne, with movies
• Java-applet based animations showing Cruithne's orbit
• A simulation of Cruithne's orbit with animation
• More Moons Around Earth?
• Information on the asteroid Cruithne
• Information on the Cruithne, the people remembered by this asteroid

References

• Nature, 1997 June 12, article by Paul A. Wiegert, Kimmo A. Innanen & Seppo Mikkola
• "More Mathematical Astronomy Morsels", Jean Meeus, chapter 38: "Cruithne, an asteroid with a remarkable orbit"