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Zoom Astronomy Questions and Answers March 2001

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We enjoy hearing from visitors. Thank you for writing! You can send us your astronomy question and we'll try to answer as soon as possible (but we can't answer all the questions we receive).

Don't forget to scroll down to find the answer to your question - they're in reverse order by the date they were asked.

Zoom Astronomy Questions
Current Questions November 2001 October 2001 September 2001 August 2001 June-July 2001 May 2001 April 2001 March 2001

from LACOYA C., FAIRFIELD, CA, USA; March 30, 2001

A: It takes 224.7 Earth days for Venus to revolve around the Sun once.

Q: How many asteroids are there?
from Daniel R, Waukesha, ?, USA; March 30, 2001

A: There are about 40,000 known asteroids that are over 0.5 miles (1 km) in diameter in the asteroid belt. There are many more smaller asteroids. About 3,000 asteroids have been cataloged..

Q: Steller nursrys to giant stars. Where to from gaint stars?
from Christina B., Danbury, CT, United States; March 29, 2001

A: It depends on the mass of the giant star. Stars that start out about the mass of our Sun will turn into a red giant and then into a black dwarf. Stars that are from 1.5 to 3 times the mass of the Sun will end up as a neutron star. Stars that are over 3 times the mass of the Sun will end up as a black hole. For more information, click here.

Q: We are studying planets and moons in our homeschool this month, and one of our activities is to find out how many "earth days" it takes for each planet to orbit the sun, and then to figure out how old my daughter would be on each planet. I thought this would be easy information to find, but so far, it hasn't been! Thanks for your help.
from Mary Ann K, Fredericksburg, VA, USA; March 29, 2001

A: For a page where you can enter your age and find out how old you are on the planets, click here. That page also lists how long a year is on each planet (in Earth days or Earth years).

Q: what causes the highest of the high tides and the lowest of the low tides?
from mindi a., marysville, wa, usa; March 29, 2001

Proxigean tide
The eccentricity of the orbit of the moon in this illustration is greatly exaggerated.
The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years.

Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.

Q: 1. When were planets first discovered? How many were first discovered and who discoverered them?

2.What was the last planet to be discovered outside of our solar system?

3.Have planets been discovered outside of our solar system?

4. When were telescopes first used to view the planets?

5. Who was the first scientist to study the planets using a telescope?

6. How many moons does each planet have?

7. What is gravity like on each planet? Is it different from the gravity on Earth? What does gravity have to do with the planets staying in orbit around the sun?

I'm sorry there's so many questions but my daughter is having a hard time on her assignment.
Thank you, Wednesday M.

from Wednesday M, St. Petersburg, FL, USA; March 27, 2001

A: 1. Many planets are visible to the naked eye (Mercury, Venus, Mars, Jupiter, and Saturn) - these planets have been known since ancient times. As for the rest, Uranus was discovered in 1781 by William Herschel, Neptune was discovered in 1846 by Galle and d'Arrest, and Pluto was discovered by Tombaugh in 1930.

2. I'm not sure which was the last one discovered - many have been discovered recently.

3. Yes, many other solar systems have been discovered.

4. Galileo first used a telescope to look at the planets in the early 1600's.

5. Galileo Galilei

6. Number of planetary moons: Mercury-0, Venus-0, Earth-1, Mars-2, Jupiter 16+, Saturn-18 named + many smaller ones, Uranus-2, Neptune-2, Pluto-1.

gravity on planets7. The force of gravity is different on each of the planets (on some planets, you would feel lighter than you do on Earth, on others, you would feel heavier). Gravity is the force that keeps the planets in orbit around the Sun.

Q: Why do stars twinkle?
from Ma. Lucy Anna Espuerta, Auckland, New Zealand, New Zealand; March 22, 2001

A: The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.

Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).

Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent).

Stars would not appear to twinkle if we viewed them from outer space (or from a planets/moon that didn't have an atmosphere).

Zoom Astronomy Questions
Current Questions November 2001 October 2001 September 2001 August 2001 June-July 2001 May 2001 April 2001 March 2001

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