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In celestial mechanics, **escape velocity** or **escape speed** is the minimum speed needed for an object to escape from contact with or orbit of a primary body, assuming:

- Calculation
- Earth
- Energy required
- Conservation of energy
- Relativistic
- Scenarios
- From the surface of a body
- From a rotating body
- Practical considerations
- From an orbiting body
- Barycentric escape velocity
- Height of lower-velocity trajectories
- Trajectory
- List of escape velocities
- Deriving escape velocity using calculus
- See also
- Notes
- References
- External links

- Ballistic trajectory - no other forces are acting on the object, including propulsion and friction
- No other gravity-producing objects exist

Although the term *escape velocity* is common, it is more accurately described as a speed than a velocity because it is independent of direction. Because gravitational force between two objects depends on their combined mass, the escape speed also depends on mass. For artificial satellites and small natural objects, the mass of the object makes a negligible contribution to the combined mass, and so is often ignored.

Escape speed varies with distance from the center of the primary body, as does the velocity of an object traveling under the gravitational influence of the primary. If an object is in a circular or elliptical orbit, its speed is always less than the escape speed at its current distance. In contrast if it is on a hyperbolic trajectory its speed will always be higher than the escape speed at its current distance. (It will slow down as it gets to greater distance, but do so asymptotically approaching a positive speed.) An object on a parabolic trajectory will always be traveling exactly the escape speed at its current distance. It has precisely balanced positive kinetic energy and negative gravitational potential energy;^{ [lower-alpha 1] } it will always be slowing down, asymptotically approaching zero speed, but never quite stop.^{ [1] }

Escape velocity calculations are typically used to determine whether an object will remain in the gravitational sphere of influence of a given body. For example, in solar system exploration it is useful to know whether a probe will continue to orbit the Earth or escape to a heliocentric orbit. It is also useful to know how much a probe will need to slow down in order to be gravitationally captured by its destination body. Rockets do not have to reach escape velocity in a single maneuver, and objects can also use a gravity assist to siphon kinetic energy away from large bodies.

Precise trajectory calculations require taking into account small forces like atmospheric drag, radiation pressure, and solar wind. A rocket under continuous or intermittent thrust (or an object climbing a space elevator) can attain escape at any non-zero speed, but the minimum amount of energy required to do so is always the same.

Escape speed at a distance *d* from the center of a spherically symmetric primary body (such as a star or a planet) with mass *M* is given by the formula^{ [2] }^{ [3] }

where:

*G*is the universal gravitational constant (*G*≈ 6.67×10^{−11}m^{3}·kg^{−1}·s^{−2})*g*=*GM/d*is the local gravitational acceleration (or the surface gravity, when^{2}*d*=*r*).

The value *GM* is called the standard gravitational parameter, or *μ*, and is often known more accurately than either *G* or *M* separately.

When given an initial speed greater than the escape speed the object will asymptotically approach the * hyperbolic excess speed * satisfying the equation:^{ [4] }

For example, an agreed upon, definitional value for standard gravity is 9.80665 m/s^{2} (32.1740 ft/s^{2}).^{ [5] } and the escape velocity is 11.186 km/s (40,270 km/h; 25,020 mph; 36,700 ft/s).^{ [6] } This is approximately 33 times the speed of sound (Mach 33) and several times the muzzle velocity of a rifle bullet (up to 1.7 km/s).^{[ citation needed ]}^{[ original research? ]} At 9,000 km altitude, escape velocity is slightly less than 7.1 km/s.^{[ citation needed ]} These velocities are relative to a non-rotating frame of reference; launching near the equator rather than the poles can actually provide a boost.^{[ citation needed ]}

In this context, when taking Earth as the primary body, escape velocity is sometimes called the "second cosmic velocity".^{[ citation needed ]}

For an object of mass the energy required to escape the Earth's gravitational field is *GMm / r*, a function of the object's mass (where *r* is radius of the Earth, nominally 6,371 kilometres (3,959 mi), *G* is the gravitational constant, and *M* is the mass of the Earth, *M* = 5.9736 × 10^{24} kg). A related quantity is the specific orbital energy which is essentially the sum of the kinetic and potential energy divided by the mass. An object has reached escape velocity when the specific orbital energy is greater than or equal to zero.

The existence of escape velocity can be thought of as a consequence of conservation of energy and an energy field of finite depth. For an object with a given total energy, which is moving subject to conservative forces (such as a static gravity field) it is only possible for the object to reach combinations of locations and speeds which have that total energy; places which have a higher potential energy than this cannot be reached at all. Adding speed (kinetic energy) to an object expands the region of locations it can reach, until, with enough energy, everywhere to infinity becomes accessible.

The formula for escape velocity can be derived from the principle of conservation of energy. For the sake of simplicity, unless stated otherwise, we assume that an object will escape the gravitational field of a uniform spherical planet by moving away from it and that the only significant force acting on the moving object is the planet's gravity. Imagine that a spaceship of mass *m* is initially at a distance *r* from the center of mass of the planet, whose mass is *M*, and its initial speed is equal to its escape velocity, . At its final state, it will be an infinite distance away from the planet, and its speed will be negligibly small. Kinetic energy *K* and gravitational potential energy *U _{g}* are the only types of energy that we will deal with (we will ignore the drag of the atmosphere), so by the conservation of energy,

We can set *K*_{final} = 0 because final velocity is arbitrarily small, and *U _{g}*

The same result is obtained by a relativistic calculation, in which case the variable *r* represents the *radial coordinate* or *reduced circumference* of the Schwarzschild metric.^{ [8] }^{ [9] }

An alternative expression for the escape velocity particularly useful at the surface on the body is:

where *r* is the distance between the center of the body and the point at which escape velocity is being calculated and *g* is the gravitational acceleration at that distance (i.e., the surface gravity).^{ [10] }

For a body with a spherically symmetric distribution of mass, the escape velocity from the surface is proportional to the radius assuming constant density, and proportional to the square root of the average density ρ.

where

This escape velocity is relative to a non-rotating frame of reference, not relative to the moving surface of the planet or moon, as explained below.

The escape velocity *relative to the surface* of a rotating body depends on direction in which the escaping body travels. For example, as the Earth's rotational velocity is 465 m/s at the equator, a rocket launched tangentially from the Earth's equator to the east requires an initial velocity of about 10.735 km/s *relative to the moving surface at the point of launch* to escape whereas a rocket launched tangentially from the Earth's equator to the west requires an initial velocity of about 11.665 km/s *relative to that moving surface*. The surface velocity decreases with the cosine of the geographic latitude, so space launch facilities are often located as close to the equator as feasible, e.g. the American Cape Canaveral (latitude 28°28′ N) and the French Guiana Space Centre (latitude 5°14′ N).

In most situations it is impractical to achieve escape velocity almost instantly, because of the acceleration implied, and also because if there is an atmosphere, the hypersonic speeds involved (on Earth a speed of 11.2 km/s, or 40,320 km/h) would cause most objects to burn up due to aerodynamic heating or be torn apart by atmospheric drag. For an actual escape orbit, a spacecraft will accelerate steadily out of the atmosphere until it reaches the escape velocity appropriate for its altitude (which will be less than on the surface). In many cases, the spacecraft may be first placed in a parking orbit (e.g. a low Earth orbit at 160–2,000 km) and then accelerated to the escape velocity at that altitude, which will be slightly lower (about 11.0 km/s at a low Earth orbit of 200 km). The required additional change in speed, however, is far less because the spacecraft already has a significant orbital speed (in low Earth orbit speed is approximately 7.8 km/s, or 28,080 km/h).

The escape velocity at a given height is times the speed in a circular orbit at the same height, (compare this with the velocity equation in circular orbit). This corresponds to the fact that the potential energy with respect to infinity of an object in such an orbit is minus two times its kinetic energy, while to escape the sum of potential and kinetic energy needs to be at least zero. The velocity corresponding to the circular orbit is sometimes called the **first cosmic velocity**, whereas in this context the escape velocity is referred to as the **second cosmic velocity**.^{ [11] }

For a body in an elliptical orbit wishing to accelerate to an escape orbit the required speed will vary, and will be greatest at periapsis when the body is closest to the central body. However, the orbital speed of the body will also be at its highest at this point, and the change in velocity required will be at its lowest, as explained by the Oberth effect.

Escape velocity can either be measured as relative to the other, central body or relative to center of mass or barycenter of the system of bodies. Thus for systems of two bodies, the term *escape velocity* can be ambiguous, but it is usually intended to mean the barycentric escape velocity of the less massive body. Escape velocity usually refers to the escape velocity of zero mass test particles. For zero mass test particles we have that the 'relative to the other' and the 'barycentric' escape velocities are the same, namely .

But when we can't neglect the smaller mass (say ) we arrive at slightly different formulas.

Because the system has to obey the law of conservation of momentum we see that both the larger and the smaller mass must be accelerated in the gravitational field. Relative to the center of mass the velocity of the larger mass ( , for planet) can be expressed in terms of the velocity of the smaller mass (, for rocket). We get .

The 'barycentric' escape velocity now becomes : while the 'relative to the other' escape velocity becomes : .

Ignoring all factors other than the gravitational force between the body and the object, an object projected vertically at speed from the surface of a spherical body with escape velocity and radius will attain a maximum height satisfying the equation^{ [12] }

which, solving for *h* results in

where is the ratio of the original speed to the escape velocity

Unlike escape velocity, the direction (vertically up) is important to achieve maximum height.

If an object attains exactly escape velocity, but is not directed straight away from the planet, then it will follow a curved path or trajectory. Although this trajectory does not form a closed shape, it can be referred to as an orbit. Assuming that gravity is the only significant force in the system, this object's speed at any point in the trajectory will be equal to the escape velocity *at that point* due to the conservation of energy, its total energy must always be 0, which implies that it always has escape velocity; see the derivation above. The shape of the trajectory will be a parabola whose focus is located at the center of mass of the planet. An actual escape requires a course with a trajectory that does not intersect with the planet, or its atmosphere, since this would cause the object to crash. When moving away from the source, this path is called an escape orbit. Escape orbits are known as *C3* = 0 orbits. *C3* is the characteristic energy, = −*GM*/2*a*, where *a* is the semi-major axis, which is infinite for parabolic trajectories.

If the body has a velocity greater than escape velocity then its path will form a hyperbolic trajectory and it will have an excess hyperbolic velocity, equivalent to the extra energy the body has. A relatively small extra delta-*v* above that needed to accelerate to the escape speed can result in a relatively large speed at infinity. Some orbital manoeuvres make use of this fact. For example, at a place where escape speed is 11.2 km/s, the addition of 0.4 km/s yields a hyperbolic excess speed of 3.02 km/s:

If a body in circular orbit (or at the periapsis of an elliptical orbit) accelerates along its direction of travel to escape velocity, the point of acceleration will form the periapsis of the escape trajectory. The eventual direction of travel will be at 90 degrees to the direction at the point of acceleration. If the body accelerates to beyond escape velocity the eventual direction of travel will be at a smaller angle, and indicated by one of the asymptotes of the hyperbolic trajectory it is now taking. This means the timing of the acceleration is critical if the intention is to escape in a particular direction.

If the speed at periapsis is v, then the eccentricity of the trajectory is given by:

This is valid for elliptical, parabolic, and hyperbolic trajectories. If the trajectory is hyperbolic or parabolic, it will asymptotically approach an angle from the direction at periapsis, with

The speed will asymptotically approach

In this table, the left-hand half gives the escape velocity from the visible surface (which may be gaseous as with Jupiter for example), relative to the centre of the planet or moon (that is, not relative to its moving surface). In the right-hand half, *V _{e}* refers to the speed relative to the central body (for example the sun), whereas

Location | Relative to | V (km/s)_{e}^{ [13] } | Location | Relative to | V (km/s)_{e}^{ [13] } | System escape, V (km/s)_{te} | |
---|---|---|---|---|---|---|---|

On the Sun | The Sun's gravity | 617.5 | |||||

On Mercury | Mercury's gravity | 4.25 | At Mercury | The Sun's gravity | ~ 67.7 | ~ 20.3 | |

On Venus | Venus's gravity | 10.36 | At Venus | The Sun's gravity | 49.5 | 17.8 | |

On Earth | Earth's gravity | 11.186 | At Earth | The Sun's gravity | 42.1 | 16.6 | |

On the Moon | The Moon's gravity | 2.38 | At the Moon | Earth's gravity | 1.4 | 2.42 | |

On Mars | Mars' gravity | 5.03 | At Mars | The Sun's gravity | 34.1 | 11.2 | |

On Ceres | Ceres's gravity | 0.51 | At Ceres | The Sun's gravity | 25.3 | 7.4 | |

On Jupiter | Jupiter's gravity | 60.20 | At Jupiter | The Sun's gravity | 18.5 | 60.4 | |

On Io | Io's gravity | 2.558 | At Io | Jupiter's gravity | 24.5 | 7.6 | |

On Europa | Europa's gravity | 2.025 | At Europa | Jupiter's gravity | 19.4 | 6.0 | |

On Ganymede | Ganymede's gravity | 2.741 | At Ganymede | Jupiter's gravity | 15.4 | 5.3 | |

On Callisto | Callisto's gravity | 2.440 | At Callisto | Jupiter's gravity | 11.6 | 4.2 | |

On Saturn | Saturn's gravity | 36.09 | At Saturn | The Sun's gravity | 13.6 | 36.3 | |

On Titan | Titan's gravity | 2.639 | At Titan | Saturn's gravity | 7.8 | 3.5 | |

On Uranus | Uranus' gravity | 21.38 | At Uranus | The Sun's gravity | 9.6 | 21.5 | |

On Neptune | Neptune's gravity | 23.56 | At Neptune | The Sun's gravity | 7.7 | 23.7 | |

On Triton | Triton's gravity | 1.455 | At Triton | Neptune's gravity | 6.2 | 2.33 | |

On Pluto | Pluto's gravity | 1.23 | At Pluto | The Sun's gravity | ~ 6.6 | ~ 2.3 | |

200 AU from the Sun | The Sun's gravity | 2.98^{ [14] } | |||||

1774 AU from the Sun | The Sun's gravity | 1^{ [14] } | |||||

At Solar System galactic radius | The Milky Way's gravity | 492–594^{ [15] }^{ [16] } | |||||

On the event horizon | A black hole's gravity | 299,792.458 (speed of light) |

The last two columns will depend precisely where in orbit escape velocity is reached, as the orbits are not exactly circular (particularly Mercury and Pluto).

Let *G* be the gravitational constant and let *M* be the mass of the earth (or other gravitating body) and *m* be the mass of the escaping body or projectile. At a distance *r* from the centre of gravitation the body feels an attractive force

The work needed to move the body over a small distance *dr* against this force is therefore given by

The total work needed to move the body from the surface *r*_{0} of the gravitating body to infinity is then^{ [17] }

In order to do this work to reach infinity, the body's minimal kinetic energy at departure must match this work, so the escape velocity *v*_{0} satisfies

which results in

- Black hole – an object with an escape velocity greater than the speed of light
- Characteristic energy (C
_{3}) - Delta-v budget – speed needed to perform maneuvers.
- Gravitational slingshot – a technique for changing trajectory
- Gravity well
- List of artificial objects in heliocentric orbit
- List of artificial objects leaving the Solar System
- Newton's cannonball
- Oberth effect – burning propellant deep in a gravity field gives higher change in kinetic energy
- Two-body problem

- ↑ Gravitational potential energy is defined to be zero at an infinite distance.

In celestial mechanics, an **orbit** is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.

In classical mechanics, **free fall** is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on it.

In astronautics, the **Hohmann transfer orbit** is an orbital maneuver used to transfer a spacecraft between two orbits of different altitudes around a central body. For example, a Hohmann transfer could be used to raise a satellite's orbit from low Earth orbit to geostationary orbit. In the idealized case, the initial and target orbits are both circular and coplanar. The maneuver is accomplished by placing the craft into an elliptical transfer orbit that is tangential to both the initial and target orbits. The maneuver uses two impulsive engine burns: the first establishes the transfer orbit, and the second adjusts the orbit to match the target.

**Orbital mechanics** or **astrodynamics** is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets, satellites, and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the law of universal gravitation. Orbital mechanics is a core discipline within space-mission design and control.

In gravitationally bound systems, the **orbital speed** of an astronomical body or object is the speed at which it orbits around either the barycenter or, if one body is much more massive than the other bodies of the system combined, its speed relative to the center of mass of the most massive body.

The **Hill sphere** is a common model for the calculation of a gravitational sphere of influence. It is the most commonly used model to calculate the spatial extent of gravitational influence of an astronomical body (*m*) in which it dominates over the gravitational influence of other bodies, particularly a primary (*M*). It is sometimes confused with other models of gravitational influence, such as the Laplace sphere or being called the **Roche sphere**, the latter causing confusion with the Roche limit. It was defined by the American astronomer George William Hill, based on the work of the French astronomer Édouard Roche.

**Gravitational time dilation** is a form of time dilation, an actual difference of elapsed time between two events, as measured by observers situated at varying distances from a gravitating mass. The lower the gravitational potential, the slower time passes, speeding up as the gravitational potential increases. Albert Einstein originally predicted this in his theory of relativity, and it has since been confirmed by tests of general relativity.

In astrodynamics or celestial mechanics a **parabolic trajectory** is a Kepler orbit with the eccentricity equal to 1 and is an unbound orbit that is exactly on the border between elliptical and hyperbolic. When moving away from the source it is called an **escape orbit**, otherwise a **capture orbit**. It is also sometimes referred to as a **C _{3} = 0 orbit** (see Characteristic energy).

In astrodynamics or celestial mechanics, a **hyperbolic trajectory** or **hyperbolic orbit** is the trajectory of any object around a central body with more than enough speed to escape the central object's gravitational pull. The name derives from the fact that according to Newtonian theory such an orbit has the shape of a hyperbola. In more technical terms this can be expressed by the condition that the orbital eccentricity is greater than one.

In astrodynamics, the **characteristic energy** is a measure of the excess specific energy over that required to just barely escape from a massive body. The units are length^{2} time^{−2}, i.e. velocity squared, or energy per mass.

In astrodynamics or celestial mechanics, an **elliptic orbit** or **elliptical orbit** is a Kepler orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1. In a wider sense, it is a Kepler orbit with negative energy. This includes the **radial elliptic orbit**, with eccentricity equal to 1.

A **circular orbit** is an orbit with a fixed distance around the barycenter; that is, in the shape of a circle. In this case, not only the distance, but also the speed, angular speed, potential and kinetic energy are constant. There is no periapsis or apoapsis. This orbit has no radial version.

In the gravitational two-body problem, the **specific orbital energy** of two orbiting bodies is the constant sum of their mutual potential energy and their total kinetic energy, divided by the reduced mass. According to the orbital energy conservation equation, it does not vary with time: where

In astrodynamics, an **orbit equation** defines the path of orbiting body around central body relative to , without specifying position as a function of time. Under standard assumptions, a body moving under the influence of a force, directed to a central body, with a magnitude inversely proportional to the square of the distance, has an orbit that is a conic section with the central body located at one of the two foci, or *the* focus.

In astrodynamics, the ** vis-viva equation**, also referred to as

**Spacecraft flight dynamics** is the application of mechanical dynamics to model how the external forces acting on a space vehicle or spacecraft determine its flight path. These forces are primarily of three types: propulsive force provided by the vehicle's engines; gravitational force exerted by the Earth and other celestial bodies; and aerodynamic lift and drag.

A **gravity train** is a theoretical means of transportation for purposes of commuting between two points on the surface of a sphere, by following a straight tunnel connecting the two points through the interior of the sphere.

A set of **equations** describing the trajectories of objects subject to a constant gravitational force under normal Earth-bound conditions. Assuming constant acceleration *g* due to Earth’s gravity, Newton's law of universal gravitation simplifies to *F* = *mg*, where *F* is the force exerted on a mass *m* by the Earth’s gravitational field of strength *g*. Assuming constant *g* is reasonable for objects falling to Earth over the relatively short vertical distances of our everyday experience, but is not valid for greater distances involved in calculating more distant effects, such as spacecraft trajectories.

In geometry, the **major axis** of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The **semi-major axis** is the longest semidiameter or one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter. The **semi-minor axis** of an ellipse or hyperbola is a line segment that is at right angles with the semi-major axis and has one end at the center of the conic section. For the special case of a circle, the lengths of the semi-axes are both equal to the radius of the circle.

In astrodynamics and celestial mechanics a **radial trajectory ** is a Kepler orbit with zero angular momentum. Two objects in a radial trajectory move directly towards or away from each other in a straight line.

- ↑ Giancoli, Douglas C. (2008).
*Physics for Scientists and Engineers with Modern Physics*. Addison-Wesley. p. 199. ISBN 978-0-13-149508-1. - ↑ Jim Breithaupt (2000).
*New Understanding Physics for Advanced Level*(illustrated ed.). Nelson Thornes. p. 231. ISBN 978-0-7487-4314-8. Extract of page 231 - ↑ Khatri, Poudel, Gautam, M.K., P.R., A.K. (2010).
*Principles of Physics*. Kathmandu: Ayam Publication. pp. 170, 171. ISBN 9789937903844.`{{cite book}}`

: CS1 maint: multiple names: authors list (link) - ↑ Bate, Roger R.; Mueller, Donald D.; White, Jerry E. (1971).
*Fundamentals of Astrodynamics*(illustrated ed.). Courier Corporation. p. 39. ISBN 978-0-486-60061-1. - ↑ Bureau International des Poids et Mesures (1901). "Déclaration relative à l'unité de masse et à la définition du poids; valeur conventionnelle de
*g*_{n}".*Comptes Rendus des Séances de la Troisième Conférence· Générale des Poids et Mesures*(in French). Paris: Gauthier-Villars. p. 68.Le nombre adopté dans le Service international des Poids et Mesures pour la valeur de l'accélération normale de la pesanteur est 980,665 cm/sec², nombre sanctionné déjà par quelques législations. Déclaration relative à l'unité de masse et à la définition du poids; valeur conventionnelle de

*g*_{n}. - ↑ Lai, Shu T. (2011).
*Fundamentals of Spacecraft Charging: Spacecraft Interactions with Space Plasmas*. Princeton University Press. p. 240. ISBN 978-1-4008-3909-4. This is a tabulation of physical constants in relation to the launch of satelites from the Earth. Only the metric value of the escape velocity appears here. - ↑ "NASA – NSSDC – Spacecraft – Details". Archived from the original on 2 June 2019. Retrieved 21 August 2019.
- ↑ Taylor, Edwin F.; Wheeler, John Archibald; Bertschinger, Edmund (2010).
*Exploring Black Holes: Introduction to General Relativity*(2nd revised ed.). Addison-Wesley. pp. 2–22. ISBN 978-0-321-51286-4. Sample chapter, page 2-22 Archived 21 July 2017 at the Wayback Machine - ↑ Choquet-Bruhat, Yvonne (2015).
*Introduction to General Relativity, Black Holes, and Cosmology*(illustrated ed.). Oxford University Press. pp. 116–117. ISBN 978-0-19-966646-1. - ↑ Bate, Mueller and White, p. 35
- ↑ Teodorescu, P. P. (2007).
*Mechanical systems, classical models*. Springer, Japan. p. 580. ISBN 978-1-4020-5441-9., Section 2.2.2, p. 580 - ↑ Bajaj, N. K. (2015).
*Complete Physics: JEE Main*. McGraw-Hill Education. p. 6.12. ISBN 978-93-392-2032-7. Example 21, page 6.12 - 1 2 For planets: "Planets and Pluto : Physical Characteristics". NASA . Retrieved 18 January 2017.
- 1 2 "To the Voyagers and escaping from the Sun". Initiative for Interstellar Studies. 25 February 2015. Retrieved 3 February 2023.
- ↑ Smith, Martin C.; Ruchti, G. R.; Helmi, A.; Wyse, R. F. G. (2007). "The RAVE Survey: Constraining the Local Galactic Escape Speed".
*Proceedings of the International Astronomical Union*.**2**(S235): 755–772. arXiv: astro-ph/0611671 . Bibcode:2007IAUS..235..137S. doi:10.1017/S1743921306005692. S2CID 125255461. - ↑ Kafle, P.R.; Sharma, S.; Lewis, G.F.; Bland-Hawthorn, J. (2014). "On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution".
*The Astrophysical Journal*.**794**(1): 17. arXiv: 1408.1787 . Bibcode:2014ApJ...794...59K. doi:10.1088/0004-637X/794/1/59. S2CID 119040135. - ↑ Muncaster, Roger (1993).
*A-level Physics*(illustrated ed.). Nelson Thornes. p. 103. ISBN 978-0-7487-1584-8. Extract of page 103

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