Much of the Solar System is still unknown.

Areas beyond thousands of AU away are still virtually unmapped and learning
about this region of space is difficult. Study in this region depends upon inferences from those few objects whose orbits
happen to be perturbed such that they fall closer to the Sun, and even then, detecting these objects has often been possible
only when they happened to become bright enough to register as comets.[244] Many objects may yet be discovered in the
Solar System's uncharted regions.[245]
One of these objects might be the Oort cloud, a theorized spherical cloud of up to a trillion icy objects that is thought to be
the source for all long-period comets.[246][247] No direct observation of the Oort cloud is possible with present imaging
technology.[248] It is theorized to surround the Solar System at roughly 50,000 AU (~0.9 ly) from the Sun and possibly to as far
as 100,000 AU (~1.8 ly). The Oort cloud is thought to be composed of comets that were ejected from the inner Solar System
by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent
events, such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky
Way.[246][247]
As of the 2020s, a few astronomers have hypothesized that Planet Nine (a planet beyond Neptune) might exist, based on
statistical variance in the orbit of extreme trans-Neptunian objects.[249] Their closest approaches to the Sun are mostly
clustered around one sector and their orbits are similarly tilted, suggesting that a large planet might be influencing their orbit
over millions of years.[250][251][252] However, some astronomers said that this observation might be credited to observational
biases or just sheer coincidence.[253]
The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light-
years (125,000 AU). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than 50,000 AU.
[254]
Most of the mass is orbiting in the region between 3,000 and 100,000 AU.[255] The furthest known objects, such as Comet
West, have aphelia around 70,000 AU from the Sun.[256] The Sun's Hill sphere with respect to the galactic nucleus, the
effective range of its gravitational influence, is thought to extend up to a thousand times farther and encompasses the
hypothetical Oort cloud.[257] It was calculated by Chebotarev to be 230,000 au.[7]

The Solar
System within the interstellar medium, with the different regions and their distances on a steped
horizontal distance scale

Celestial neighborhood
Main articles: List of nearest stars and brown dwarfs, List of nearest exoplanets, and List of nearby stellar associations and
moving groups
 Diagram of the Local Interstellar Cloud, the G-Cloud and
surrounding stars. As of 2022, the precise location of the Solar System in the clouds is an open question
in astronomy. [258]

Within ten light-years of the Sun there are relatively few stars, the closest being the triple star system Alpha Centauri, which
is about 4.4 light-years away and may be in the Local Bubble's G-Cloud.[259] Alpha Centauri A and B are a closely tied pair
of Sun-like stars, whereas the closest star to Sun, the small red dwarf Proxima Centauri, orbits the pair at a distance of 0.2
light-years. In 2016, a potentially habitable exoplanet was found to be orbiting Proxima Centauri, called Proxima Centauri b,
the closest confirmed exoplanet to the Sun.[260]
The Solar System is surrounded by the Local Interstellar Cloud, although it is not clear if it is embedded in the Local
Interstellar Cloud or if it lies just outside the cloud's edge.[261] Multiple other interstellar clouds exist in the region within 300
light-years of the Sun, known as the Local Bubble.[261] The latter feature is an hourglass-shaped cavity or superbubble in the
interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it
may be the product of several recent supernovae.[262]
The Local Bubble is a small superbubble compared to the neighboring wider Radcliffe Wave and Split linear structures
(formerly Gould Belt), each of which are some thousands of light-years in length.[263] All these structures are part of the Orion
Arm, which contains most of the stars in the Milky Way that are visible to the unaided eye.[264]
Groups of stars form together in star clusters, before dissolving into co-moving associations. A prominent grouping that is
visible to the naked eye is the Ursa Major moving group, which is around 80 light-years away within the Local Bubble. The
nearest star cluster is Hyades, which lies at the edge of the Local Bubble. The closest star-forming regions are the Corona
Australis Molecular Cloud, the Rho Ophiuchi cloud complex and the Taurus molecular cloud; the latter lies just beyond the
Local Bubble and is part of the Radcliffe wave.[265]
Stellar flybys that pass within 0.8 light-years of the Sun occur roughly once every 100,000 years. The closest well-measured
approach was Scholz's Star, which approached to ~50,000 AU of the Sun some ~70 thousands years ago, likely passing
through the outer Oort cloud.[266] There is a 1% chance every billion years that a star will pass within 100 AU of the Sun,
potentially disrupting the Solar System.[267]

Galactic position
See also: Location of Earth, Galactic year, and Orbit of the Sun
 Diagram of the Milky Way, with galactic features and the relative
position of the Solar System labelled.

The Solar System is located in the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years containing
more than 100 billion stars.[268] The Sun is part of one of the Milky Way's outer spiral arms, known as the Orion–Cygnus
Arm or Local Spur.[269][270]
Its speed around the center of the Milky Way is about 220 km/s, so that it completes one revolution every 240 million years.
[268]
This revolution is known as the Solar System's galactic year.[271] The solar apex, the direction of the Sun's path through
interstellar space, is near the constellation Hercules in the direction of the current location of the bright star Vega.[272] The
plane of the ecliptic lies at an angle of about 60° to the galactic plane.[c]
The Sun follows a nearly circular orbit around the Galactic Center (where the supermassive black hole Sagittarius
A* resides) at a distance of 26,660 light-years,[274] orbiting at roughly the same speed as that of the spiral arms.[275] If it orbited
close to the center, gravitational tugs from nearby stars could perturb bodies in the Oort cloud and send many comets into
the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. In this scenario, the
intense radiation of the Galactic Center could interfere with the development of complex life.[275]
The Solar System's location in the Milky Way is a factor in the evolutionary history of life on Earth. Spiral arms are home to a
far larger concentration of supernovae, gravitational instabilities, and radiation that could disrupt the Solar System, but since
Earth stays in the Local Spur and therefore does not pass frequently through spiral arms, this has given Earth long periods
of stability for life to evolve.[275] However, according to the controversial Shiva hypothesis, the changing position of the Solar
System relative to other parts of the Milky Way could explain periodic extinction events on Earth.[276][277]

Humanity's perspective
Discovery and exploration
Main article: Discovery and exploration of the Solar System

The motion of 'lights' moving across the sky is the basis of the
classical definition of planets: wandering stars.
Humanity's knowledge of the Solar System has grown incrementally over the centuries. Up to the Late Middle Ages–
Renaissance, astronomers from Europe to India believed Earth to be stationary at the center of the universe[278] and
categorically different from the divine or ethereal objects that moved through the sky. Although
the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus
Copernicus was the first person known to have developed a mathematically predictive heliocentric system.[279][280]
Heliocentrism did not triumph immediately over geocentrism, but the work of Copernicus had its champions,
notably Johannes Kepler. Using a heliocentric model that improved upon Copernicus by allowing orbits to be elliptical, and
the precise observational data of Tycho Brahe, Kepler produced the Rudolphine Tables, which enabled accurate
computations of the positions of the then-known planets. Pierre Gassendi used them to predict a transit of Mercury in 1631,
and Jeremiah Horrocks did the same for a transit of Venus in 1639. This provided a strong vindication of heliocentrism and
Kepler's elliptical orbits.[281][282]
In the 17th century, Galileo publicized the use of the telescope in astronomy; he and Simon Marius independently
discovered that Jupiter had four satellites in orbit around it.[283] Christiaan Huygens followed on from these observations by
discovering Saturn's moon Titan and the shape of the rings of Saturn.[284] In 1677, Edmond Halley observed a transit of
Mercury across the Sun, leading him to realize that observations of the solar parallax of a planet (more ideally using the
transit of Venus) could be used to trigonometrically determine the distances between Earth, Venus, and the Sun.[285] Halley's
friend Isaac Newton, in his magisterial Principia Mathematica of 1687, demonstrated that celestial bodies are not
quintessentially different from Earthly ones: the same laws of motion and of gravity apply on Earth and in the skies.[51]: 142

True-scale Solar System diagram made by Emanuel Bowen in 1747.

The term "Solar System" entered the English language by 1704, when John Locke used it to refer to the Sun, planets, and
comets.[286] In 1705, Halley realized that repeated sightings of a comet were of the same object, returning regularly once
every 75–76 years. This was the first evidence that anything other than the planets repeatedly orbited the Sun,
[287]
though Seneca had theorized this about comets in the 1st century.[288] Careful observations of the 1769 transit of Venus
allowed astronomers to calculate the average Earth–Sun distance as 93,726,900 miles (150,838,800 km), only 0.8% greater
than the modern value.[289]
Uranus, having occasionally been observed since antiquity, was recognized to be a planet orbiting beyond Saturn by 1783.
[290]
In 1838, Friedrich Bessel successfully measured a stellar parallax, an apparent shift in the position of a star created by
Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism.[291] Neptune was identified as a
planet some years later, in 1846, than