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This Week's Questions

Question: How far have astronauts travelled into space?

Dr. Cathy answers: You may be surprised to learn that the answer is - not very far! In TV shows and movies we see people travelling all over the galaxy. Well, hopefully some day.

The farthest place that people have visited in person is our Moon. In our solar system, our Moon is "just next door". It is about 230,000 miles away from the Earth, but the farthest planet Pluto is about 3,720,000,000 (almost 4 billion) miles away. That is 16,000 times farther away than the Moon is from the Earth. The Apollo astronauts visited the Moon 6 times between 1969 and 1972. No one has gone there since.

What about the astronauts on the shuttle and at the space station? They are only 250 to 350 miles above the Earth's surface!

The picture shows astronaut "Buzz" Aldrin during the first landing on the Moon, Apollo 11. Since there is no air on the Moon to make the flag flutter in the wind, it is held up with a stick. Learn all about the Apollo astronauts' visits to the Moon at the Smithsonian's web site at

Question: How far have our spacecraft gone? Have any of them visited another star?

Dr. Cathy answers: Our spacecraft have gone much further than we have, but not to another star.

The spacecraft that have travelled the farthest are Pioneer 10 and Voyager 1. Pioneer 10 was the first spacecraft to travel through the asteroid belt and fly by Jupiter. It is now 7.4 billion miles away. For a long time, it was the farthest man-made object from the Sun, but recently Voyager 1 passed it. Pioneer is headed in the direction of the red star Aldebaran, and will pass by it in over 2 million years from now.

Voyager 1, shown in the picture, also visited Jupiter and Saturn, and has overtaken Pioneer 10 because it is travelling faster (39,000 miles per hour). It is now 7.8 billion miles away from the Sun. That is so far that it takes almost 12 hours for the radio signal to travel from the spacecraft back to Earth.

By the way the nearest star, alpha Centauri, is about 24 trillion (24 followed by 12 zeroes) miles away!

Read questions and answers from previous weeks...     GO!

What would you like to know about astronomy and space? Send your questions to me, Dr. Cathy, by email or mail, and I will choose two or three questions per week to answer fully on this website. Teachers, you can arrange a special question/answer session with Dr. Cathy - just email me first to set this up!

To email your question, please send a message to me at

To mail your question via the Post Office, send it to:

Dr. Catherine Imhoff
Space Telescope Science Institute
3700 San Martin Blvd.
Baltimore, MD 21218

You can also check out some webpages we have online, with pictures, fun information, and links to good sources of additional information (coming soon). Select from the topics listed here:

Earth Moon Sun Mercury
Venus Mars Jupiter Saturn
Uranus Neptune Pluto Stars
Planets around other stars Constellations Black holes Galaxies
Light & color Gravity