Perihelion in the context of "Mars-crossing asteroid"

Tests of general relativity serve to establish observational evidence for the theory of general relativity. The first three tests, proposed by Albert Einstein in 1915, concerned the "anomalous" precession of the perihelion of Mercury, the bending of light in gravitational fields, and the gravitational redshift. The precession of Mercury was already known; experiments showing light bending in accordance with the predictions of general relativity were performed in 1919, with increasingly precise measurements made in subsequent tests; and scientists claimed to have measured the gravitational redshift in 1925, although measurements sensitive enough to actually confirm the theory were not made until 1954. A more accurate program starting in 1959 tested general relativity in the weak gravitational field limit, severely limiting possible deviations from the theory.

In the 1970s, scientists began to make additional tests, starting with Irwin Shapiro's measurement of the relativistic time delay in radar signal travel time near the Sun. Beginning in 1974, Russell Alan Hulse, Joseph Hooton Taylor Jr. and others studied the behaviour of binary pulsars experiencing much stronger gravitational fields than those found in the Solar System. Both in the weak field limit (as in the Solar System) and with the stronger fields present in systems of binary pulsars the predictions of general relativity have been extremely well tested.

Orcus (minor-planet designation: 90482 Orcus) is a dwarf planet located in the Kuiper belt, with one large moon, Vanth. It has an estimated diameter of 870 to 960 km (540 to 600 mi), comparable to the Inner Solar System dwarf planet Ceres. The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color, and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. Orcus was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.

Orcus is a plutino, a trans-Neptunian object that is locked in a 2:3 orbital resonance with the ice giant Neptune, making two revolutions around the Sun to every three of Neptune's. This is much like Pluto, except that the phase of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa. Orcus is the second-largest known plutino, after Pluto itself. The perihelion of Orcus's orbit is around 120° from that of Pluto, while the eccentricities and inclinations are similar. Because of these similarities and contrasts, along with its large moon Vanth that can be compared to Pluto's large moon Charon, Orcus has been dubbed the "anti-Pluto". This was a major consideration in selecting its name, as the deity Orcus was the Roman/Etruscan equivalent of the Roman/Greek Pluto.

The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to 149597870700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012.

The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec. One au is approximately equivalent to 499 light-seconds.

A sednoid is a trans-Neptunian object with a large semi-major axis, a distant perihelion and a highly eccentric orbit, similar to that of the dwarf planet Sedna. The consensus among astronomers is that there are only four objects that are known from this population: Sedna, 2012 VP113, 541132 Leleākūhonua, and 2023 KQ14. All four have perihelia greater than 60 AU. The sednoids are also classified as detached objects, since their perihelion distances are large enough that Neptune's gravity does not strongly influence their orbits. Some astronomers consider the sednoids to be Inner Oort Cloud (IOC) objects. The inner Oort cloud, or Hills cloud, lies at 1,000–10,000 AU from the Sun.

One attempt at a precise definition of sednoids is any body with a perihelion greater than 50 AU and a semi-major axis greater than 150 AU.However, this definition applies to the objects 2013 SY99, 2020 MQ53, and 2021 RR205 which have perihelia beyond 50 AU and semi-major axes over 700 AU. Despite this, astronomers do not classify these objects as sednoids because their orbits still experience gradual orbital migration as a result of perturbations by galactic tides and Neptune's weak gravitational influence.

Tempel 1 (official designation: 9P/Tempel) is a Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.6 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on 14 February 2011, and came back to perihelion in August 2016. On 26 May 2024, it made a modest approach to Jupiter at a distance of 0.55 AU (82 million km), which lifted the perihelion distance. 9P will next come to perihelion on 12 February 2028 when it will be 1.77 AU (265 million km) from the Sun.

Though no standard exists, numerous calendars and other timekeeping approaches have been proposed for the planet Mars. The most commonly seen in the scientific literature denotes the time of year as the number of degrees on its orbit from the northward equinox, and increasingly there is use of numbering the Martian years beginning at the equinox that occurred April 11, 1955.

Mars has an axial tilt and a rotation period similar to those of Earth. Thus, it experiences seasons of spring, summer, autumn and winter much like Earth. Mars's orbital eccentricity is considerably larger, which causes its seasons to vary significantly in length. A sol, or Martian day, is not that different from an Earth day: less than an hour longer. However, a Mars year is almost twice as long as an Earth year.

Caloris Planitia /kəˈlɔːrɪs pləˈnɪʃ(i)ə/ is a plain within a large impact basin on Mercury, informally named Caloris, about 1,550 km (960 mi) in diameter. It is one of the largest impact basins in the Solar System. "Calor" is Latin for "heat" and the basin is so-named because the Sun is almost directly overhead every second time Mercury passes perihelion. The crater, discovered in 1974, is surrounded by the Caloris Montes, a ring of mountains approximately 2 km (1.2 mi) tall.