# 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(106km) Mass (kg) Orbital Period Orbital Eccentricity Inclination to Earth’s Orbit Mercury 2440 57.9 3.30 x 1023 88 days 0.206 7.00 Venus 6050 108 4.87 x 1024 225 days 0.00677 3.39 Earth 6380 150 5.97 x 1024 1 yr 0.0167 0 Mars 3400 228 6.42 x 1023 1.88 yr 0.0934 1.85 Jupiter 71,500 778 1.90 x 1027 11.9 0.0484 1.31 Saturn 60,300 1430 5.69 x 1026 29.4 0.0542 2.48 Uranus 25,600 2870 8.69 x 1025 83.8 0.0472 0.770 Neptune 24,800 4500 1.02 x 1026 164 0.00859 0.770 Pluto 1150 5920 1.31 x 1022 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.)

### 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 105 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 gearth.  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.