How old is the earth?
- The oldest rocks we have found on earth are about 3.5 billion years old but meteors and lunar rocks are as old as 4,500,000,000 years old. We also calculate that the sun is about 5 billion years old and we believe that the sun, the earth, the moon, and the meteors, as well as all of the other components of the solar system, were created at about the same time.
To reach another planet, a spacecraft must be aimed:
- A spacecraft traveling to another planet becomes a miniature planet itself, traveling in an orbit around the sun. The shape of that orbit depends both on the direction and on the speed with which it leaves the earth. These must be adjusted so that the orbits of the spacecraft and the planet cross at a time when both bodies at that point.
How have astronomers learned most of what they know about the stars, galaxies, and the universe?
- See Question 1. We haven't been able to travel to the stars to observe them up close. We rely on electromagnetic radiation in the form of light, radio waves, x-rays, etc. that reachs the Earth or spacecraft orbits near Earth for most of what we know about the Universe. This is analyzed, and evaluated with what we know about physics. Theoretical models and hypotheses are developed based on these observations, and new observations are made to test those theories. Unlike most other physical scientists, astronomers cannot do controlled experiments to test their hypotheses.
How fast does the sun travel around the center of the galaxy?
- Although it takes more than 10,000,000 years for the sun to make one circuit of the galaxy, the galaxy is so large that it must travel at almost 150 miles/second to cover the distance in that time.
A brown dwarf:
- A brown dwarf is a star-like body that is too light to have enough density in its center to transform hydrogen into helium. It may transform lithium, beryllium, and boron that can be transformed at lower temperatures and densities. The difference between a brown dwarf and a planet is harder to define observationally. Normally, it is considered that a planet is created by the accretion of material around a star that has already formed. A brown dwarf can form independently of another star.
Where do most of the known asteroids orbit the Sun?
- The so-called "Asteroid Belt" lies between the orbits of Jupiter and Mars. Most of the known asteroids, including most of the large asteroids are found in this region of the Solar System.
If you could travel in a space ship at the speed of light away from the solar system, how long could you see the sun?
- The exact answer depends on your eyesight and observing conditions but most people could see the sun for about 30 years in reasonably good observing conditions. The sun is considered an average star. There are stars as much as 400,000 brighter than the sun and others as much as 400,000 time fainter if they could all be seen at the same distance.
Approximately how many stars does the Andromeda Nebula contain?
- The Andromeda Nebula (Galaxy) is often considered a twin of the Milky Way although it is a little larger. From the speed at which a star near the edge circles the center, we estimate that its mass is equal to that of 100,000,000,000 to 1,000,000,000,000 stars like the sun.
How far have spacecraft from Earth traveled into space?
- The planetary exploration missions Pioneer and Voyager have barely traveled beyond our Solar System. These are the fastest spacecraft ever launched from Earth. Even these spacecraft will take a very long time to travel one light-year. We don't have the knowledge or technology to send space probes or manned craft to even the nearest stars!
How long has light traveled from the most distant galaxy we have observed?
- A galaxy has recently been observed with a red-shift of 4.9. That means that the light we observe today has a wavelength 4.9 times its original wavelength. This is a result of the expansion of the universe. The exact distance to which this corresponds depends on details of the universe that we do not yet know. However, the distance is probably within a factor of 2 or 3 of 20,000,000,000 light years.