Gravity Fact Sheet

Physics 152 Michael Fowler 1/15/07

Gravitational acceleration g = 9.81 m/sec².

Newton’s Universal Gravitational Constant G = 6.67 x 10^-11 N.m²/kg².

The Sun has a mass of 1.99 x 10³⁰ kg, and a radius of 6.96 x 10⁸ m.

The Moon has a mass of 7.35 x 10²² kg, a radius of 1738 km., and an average orbital radius of 3.84 x 10⁵ km., and orbital period of 27.3 days. The orbital eccentricity is 0.055, the orbit is inclined at 5.15 degrees to the Earth’s orbit around the Sun.

Planetary Data

Planet	Radius (km)	Orbital Semimajor Axis(10^6km)	Mass (kg)	Orbital Period	Orbital Eccentricity	Inclination to Earth’s Orbit
Mercury	2440	57.9	3.30 x 10^23	88 days	0.206	7.00
Venus	6050	108	4.87 x 10^24	225 days	0.00677	3.39
Earth	6380	150	5.97 x 10^24	1 yr	0.0167	0
Mars	3400	228	6.42 x 10^23	1.88 yr	0.0934	1.85
Jupiter	71,500	778	1.90 x 10^27	11.9	0.0484	1.31
Saturn	60,300	1430	5.69 x 10^26	29.4	0.0542	2.48
Uranus	25,600	2870	8.69 x 10^25	83.8	0.0472	0.770
Neptune	24,800	4500	1.02 x 10^26	164	0.00859	0.770
Pluto	1150	5920	1.31 x 10^22	248	0.249	17.1

From the AIP Physics Desk Reference, Third Edition, which gives original sources, and many more details. (Except Pluto mass: that’s from http://arxiv.org/abs/astro-ph/0512491 )

Astronomical Distance Units

1 AU = 1.5 x 10¹¹m. (AU = Astronomical Unit = Earth-Sun distance.)

1 light year = 9.46 x 10¹⁵ m.

1 parsec = 3.09 x 10¹⁶ m. (= 3.27 ly.) (The distance to a star that has apparent parallax movement caused by the Earth’s orbital motion of one second of arc amplitude.)

Angle Measurement

Comparing Other Planets with the Earth

Planet	Radius compared with Earth’s	Mass compared with Earth’s	Orbital Period compared with Earth’s	g at surface compared with Earth’s
Mercury	0.382	0.0553	0.241	0.378
Venus	0.949	0.815	0.615	0.894
Earth	1	1	1	1
Mars	0.533	0.107	1.88	0.379
Jupiter	11.2	318	11.9	2.54
Saturn	9.41	95.2	29.4	1.07
Uranus	4.0	14.5	83.8	0.8
Neptune	3.9	17.2	164	1.2
Pluto	0.19	0.0021	248	0.059

And …

	Radius compared with Earth’s	Mass compared with Earth’s	g at surface compared with Earth’s
Sun	109	3.33 x 10^5	28gearth
Moon	0.272	0.0123	0.166gearth

Neutron Stars, etc.

Neutron stars are formed when stars run out of nuclear fuel and collapse (see Wikipedia.) They have masses 1.35 to 2.1 solar masses, radii between 20 and 10 km (heavier ones are smaller!). Gravity g at the surface is 2 x 10¹¹ to 3 x 10¹² g_earth. Stars with less mass form white dwarfs, about the size of the Earth, but the mass of the Sun. Collapsing stars with masses above about 3 solar masses form black holes.

Energies

Sun’s luminosity: 3.83 x 10²⁶ J/sec.

1 megaton = 4.18 x 10¹⁵ J.