Sun Earth Earth's Moon
Names of Planets and other Moons

Weights in Space MegaConverter #45 

Introduction and Overview 

Weight is a concept apart from mass in that it varies with the strength of the local gravitation field. Gravity is an unseen force that causes two things with mass to be attracted towards each other. This attraction changes with different masses and the distance between them. The equation that describes the force of gravity is 

F = G x M1 x M2 / r / r 

where G is a constant, M1 is the mass of the first object, M2 is the mass of the second object, and r is the distance between them. Thus, the force of attraction between smaller objects is less than the force between larger objects, and the force is much less for objects further away from each other. 
So that is why your weight on different planets and moons is so much different than here on Earth. 

Below are several topics of interest. We would like to especially thank the grade school class of Hellen Tai at Lynnbrook North Middle School for first suggesting this converter, and to eighth grader Alexandra Perrotta for writing the section on the Moon. 

The Sun 

The Sun is by far the largest object anywhere near us. It is what keeps the Earth and the other planets from hurtling off into space. It is so massive that if it were the same diameter of the Earth, an astronaut would be squashed flat by the gravity as soon as he got near. Even as large as it is, if you could stand on the surface of the Sun (which you can't because it's too hot), you would weigh over 27 times what you weigh on Earth. Even though the Sun is 98 million miles away from the Earth, it's gravity still affects us by causing tides to rise and fall in the ocean. 


The Earth is the planet we stand on. When we say we weigh 100 pounds, we mean that the force of gravity between our bodies and the Earth is 100 pounds. Your mass is always the same, but your weight is relative to where you are. 
You can, however, be made to appear to weigh less and be near the Earth. If you go bungee jumping or sky diving, you may feel like you weigh nothing. This is because you are in motion with respect to the Earth. The same is true of astronauts in the Space Shuttle. They only appear weightless because the shuttle is moving in orbit around the Earth. If they stood on a platform anchored to the Earth at the same height as the Shuttle, they would weigh only a little less than they do on the surface. 


 By Alexandra Perrotta 

 Have you ever wondered what it would be like to spend a day on the moon?  This information will give you more of an idea of how it would feel like plus other information on the phases, how the Earth is effected by the moon and other general information.  The moon is the only natural satellite orbiting Earth.  The moon's diameter is 3,480 km.(2,160mi.).  The mass of the Earth is 81 times greater than the moon.  Since the moon has no water, atmosphere or weather the surface will never change.  It orbits Earth at a distance of 384,403 km.(238,857 mi.) and at a speed of 3,700 km. per hour(2,300 mph).  The moon completes one revolution in an elliptical orbit in 27 days.  For the moon to go from a new moon to the next new moon it takes 29.5 days.  The same side of the moon always faces towards Earth and it reflects into space only 7% of the light that falls on it. 
  The phases of the moon depend on how much of the sunlit half can be seen.  When the moon is completely dark and cannot be seen it is called a new moon, when it is a half circle it is called the first quarter, when the moon is fully lit it is called a full moon, when the moon is in a half circle again it is called its third or last quarter.  A gibbous phase is when the moon is more than half lit and a crescent phase is when it is less than half lit.  The moon is full when it is farthest away from the sun than the Earth and it is new when it is closer to the sun than the Earth. 
  If you have ever looked at the moon with a telescope you will see a lot of dark areas.  They are called maria.  In ancient times people thought they were seas or oceans and got its name from the Latin word "maria". Maria are really lowland areas, but that's not the only feature of the moon.  There are mountain ranges, faults, domes, rilles and rays.  The entire moon has about 3 trillion craters larger than one diameter in diameter.  They were formed by fast moving meteorites or small asteroids.  The moon's surface is made up of 16% maria and much of the surface is covered with regolith, a mixture of dust and rocky debris made by meteor impacts.  Most of the rocks on the moon seem to be between 4.6 and 3 billion years old. 
  Tides are the daily rise and fall of the ocean. Tides are caused by the pull of the moon's gravity and by the sun's pull too.  There are two types of tides, spring tides and neap tides.  Spring tides are when the sun and the moon are both pulling on the water making very high and very low tides.  Neap tides are when the sun is pulling against the moon's pull causing low tides.  There are two high tides every day. 
  There are a few theories explaining how the moon was formed, but no one knows for sure.  The co-accretion theory states that the moon and earth formed at the same time from the solar nebula, the fission theory states that the moon split off the earth and another theory states that the earth hit a very large object ( as big as Mars or larger) and that the moon formed from the ejected material.  There are still some details to be worked out, but the impact theory is now widely accepted. 

For more information go to: 

Names of Planets and other Moons 

The names of the visible planets were originally given by the greeks representing their gods. The romans then renamed them in their version of the same gods. Later, when moons and other planets were discovered, they were given greek names that somehow figured in with the original theme.

Mercury or Hermes - Messenger of the gods, god of commerce.

Venus or Aphrodite - Goddess of love.

Mars or Ares - God of war. Phobos and Deimos were his children.

Jupiter or Zeus - King of the gods. Son of Saturn or Cronus. The Galilean moons (those first discovered by Galileo) were named for mistresses or boys captured by Zeus and taken to Mount Olympus. The lesser moons, discovered later,  were other gods and goddesses associated with Zeus.

Saturn or Cronus - A titan, father of the gods, and king of the universe until he was overthrown by his son Zeus. The largest moon is Titan who were the original inhabitants of the Earth, and the children of Uranus and Gaea or Heaven and Earth. The lesser moons are all Titans who figured in some way in greek mythology. 

Uranus - Uranus was the original father of the world. He represented the sky. His mate was Gaea, the Earth, and he fathered the cyclopes and the titans. Of course, Uranus was not discovered until well after Roman times, and was considered by its discoverer a progression from son to father to grandfather, ie Zeus - Cronus - Uranus. The moons of Uranus are named for fairies in greek mythology. Their names are familiar to us because they were also characters in Shakepeare's play "The Tempest."

Neptune or Poseidon - Not discovered until the 19th century, Neptune was named for the god of the deep ocean. The moon Triton was named for Poseidon's son. Nereid was a sea nymph that was loved by Poseidon. Notice that in keeping with tradition, the planet was given the roman name, but the moons were given the greek names. 

Pluto or Hades - The god of hell or the underworld. Pluto was discovered in this century. Ironically, hell is renowned for being a very hot place, but Pluto is one of the coldest places in our solar system. The moons of Pluto are named for various servants in the underworld.