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© J R Stockton, ≥ 2010-03-01

Gravity 0.

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NONE of the values given in these pages should be taken as exact, unless specifically so claimed. They have been obtained from various sources, including memory, and are for purposes of illustration ONLY, except sometimes.

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The site deals with the consequences of Newton's work; it disregards relativity, string theory, etc.

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Some Constants

There is no guarantee that these are the latest or best values. See Wikipedia, etc.

G × MSun = 1.32712440018×1020 N m2 kg-1 (HS 20031230 news:s.p.p)

G = (6.674215±0.000092)×10-11 m3/kg/s2 ( Jens H. Gundlach and Stephen M. Merkowitz);
  Earth's mass : (5.972245±0.000082)×1024 kg
  & Sun's mass : (1.988435±0.000027)×1030 kg (G & M)

Hubble constant : 70.4 ± 1.4 km/s / Mpc (68%) (WMAP, 2010)

Age of Universe : 13.75 ± 0.11 × 109 years (68%) (WMAP, 2010)

Planck density, 5.1×1096 kg/m3

Age of Solar System : 4.5685 × 109 years

Average radii : Earth : mean 6371 km, equatorial 6378 km, polar 6357 km; Moon 1739 km

Earth circumferences : polar 40007.863 km, equatorial 40075.017 km (WGS84 / Kaese))

Geosynchronous orbit radius : 42.164 Mm (authority?) ( → ~ 36 Mm high)

Standard Earth gravity : 9.80665 m s-2 (CGPM 3, 1901)

Standard atmospheric pressure at sea level : 101.325 kPa (CGPM 10, 1954)

Angles from Earth Orbit : Equator 23.4° ; Moon Orbit 5.2°

Eccentricity of Earth's orbit : currently 0.0167

Power of Sun : 3.86×1026 watts
Solar Constant : ~ 1361 W/m2.

Solar wind dynamic pressure averages ~ 2 nPa at Earth; solar radiation ~10 µPa

Measurements and Units - see in Kaye & Laby Online.

Some Equations

Uniform Sphere

Gravitational binding energy : U = 3GM2/5r

Moment of Inertia : I = 2Mr2/5


Now in The Geometry of Ellipses.

Advanced Topics

This section mentions advanced subjects that I recall comparatively little of.

Relativistic Motion

There are relativity FAQs.

A part of my Astronomy / Astronautics 3 calculates relativistic travel.

Relativistic Gravity

Note - this is really not my subject - needs checking. Was there not a third confirmation of Einstein?

The Speed of Gravity

Presumed to be that of light. Newtonian gravity is instantaneous; making the speed finite introduces unwanted differences; proper relativity removes those.

Perihelion of Mercury

The advance of the perihelion of Mercury is largely explained by Newtonian gravity. But there is a residual advance of 43" of arc per century, explained by Einstein's relativitistic gravitation.

Deviation of Light

Light passing near a massive body is deviated by gravity. Eddington's 1919 trip confirmed Einstein's relativitistic prediction of 1.74" of arc for Sun-grazing rays, twice the Newtonian value.

Gravitational Lensing

In that fashion, the Sun "focuses" light from infinity at a distance of 550 AU (the angular radius of the Sun as seen from there is 1.74"). Galaxies can focus more distant ones. Focusing is not lens-like, but it can magnify and intensify.

Blue Shift

Light reaching a massive body is gravitationally blue-shifted, and vice versa. This is not the Hubble-related shift; it can be shown locally by using the Mössbauer effect.

Black Holes

Even classically, light cannot escape from a body which is sufficiently large and concentrated, as judged by 2GM/rc2; but General Relativity is needed to attempt a full explanation of Black Holes.

One can enter a sufficiently large Black Hole unharmed, but cannot leave it nor survive long. A Black Hole must contain a singularity. Black Holes evaporate, big ones more slowly. When a large enough star runs out of fuel, it must collapse to a Black Hole?

Other Topics

The Universe - the Big Bang, inflation?, expansion/crunch?, flatness?, dark matter/energy?, cosmology?.

Galaxies - Always black holes at their centres?

The Milky Way - our Galaxy - centre in Sagittarius, a supermassive black hole (Sgr A*) orbited by many star-sized ones within ~ 1 pc.

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Gravity Pages :- 0, 1, 2, 3, 4, 5
Astronomy / Astronautics Pages :- 1, 2, 3, 4
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