Astronomy
¨ How many eclipses happen in a year?
¨ Why does the north pole and north star always point north?
¨ What seasons can the constellation Ursa Major be viewed
in from Denver?
¨ Does the earth rotate on its own axis or does it rotate
up and down?
¨ Questions about ellipticity
¨ Can the Hellas Basin crater on Mars be viewed from the
Earth?
¨ How can we imagine a universe without human beings?
¨ How would I draw a sketch of the relation between the Sun, Earth, and Moon?
¨ Streak of light across sky on September 22
¨ Why does Earth revolve around the sun?
¨ Why isn't Sirius considered part of the solar system?
¨ Has Phil Plait's Bad Astronomy
website been taken over by hackers?
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QUESTION:
How many eclipses happen in a year?
ANSWER from Imagiverse
on 21 April 2006:
Are you asking about lunar eclipses or solar eclipses? Are you asking
about total eclipses or partial eclipses or any eclipse of the sun or moon? You
can actually find this information by doing a little research on your own in
books or on the Internet. In google.com, you can type words like "eclipse
frequency". If you look up this topic in science books, you will
discover what causes an eclipse. Understanding the cause will help you
figure out the answer. If you still have a question, please rephrase
your question by being more specific and submit it again. Thank you for
contacting us!
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QUESTION:
Why does the north pole and north star always point north?
ANSWER from Roger Herzler
on 14 April 2006:
The "North Pole" is a human creation to describe one of the points
on the Earth where the Earth's rotational spin on its axis is centered. The
other point is the "South Pole". It is more a philosophical
idea that it's "north" vs. "south" or any other name. However,
the Earth rotates on its axis and it has to be called by some name.
The "North Star" or "Polaris" is
coincidentially located in the sky where the Earth's rotational center
is projected into the sky. It wasn't located by the North Pole
a few thousand years ago. In the future Polaris won't be the "North
Star" in a few hundred years because it is moving through the
galaxy just like we are. It won't be located in the proper
place to be called the "North Star" and won't be used as
a good reference to the north pole as it is today.
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QUESTION:
What seasons can the constellation Ursa Major be viewed in from Denver?
ANSWER from Roger Herzler
on 18 March 2006:
Ursa Major, part of which is known commonly as the "Big Dipper",
is visible throughout the year in all seasons in the Colorado. As the
seasons go by it simply changes apparent position around Polaris (North Star)
based on the same time every night.
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QUESTION:
Last night a thought came to me. When the sun or moon sets it goes under. That
would mean that the earth does not rotate on its own axis but rotates up and
down. Think about it and if you know something about this, please respond. I
am 10 years old and I hope that what I think is true.
ANSWER from Bonnie J.
Walters on 12 February 2006:
You have some very heavy thoughts! You also stated your question clearly
- good job. Humans have wondered the same thing since ancient times. I
don’t know where you live on this wonderful planet called Earth, but
I can assure you the Earth is spinning on its axis. One of my favorite
sites for young people your age is Harriet Witt’s Passenger Planet. If
you follow the link, it will take you to a superb demonstration of what you
are doing while "riding" on the Earth. http://www.passengerplanet.com/yourearthride.html I
hope this helps you visualize what the Earth, Moon and Sun are doing.
Take care,
Bonnie J. Walters
Astronomer
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QUESTION:
I had some questions about ellipticity that I was hoping you might be able to
help me with. I noticed that the earth’s ellipticity was 0.00335. How
specific is this number? For instance Mercury has an ellipticity of
0.000, is it really a perfect sphere? And how can I get a more accurate
number for all the planets? Any help or direction you can provide is
greatly appreciated.
ANSWER from Stephanie
Wong on 5 February 2006:
According to the Fact Sheets in http://nssdc.gsfc.nasa.gov/planetary/, where
it appears that you have gotten your info, they have listed the ellipticity
as such. Assuming that the website posts its info with consideration
of the uncertainties in measurement, the value should be accurate to the final
significant digit. Nothing is a perfect sphere, but it appears Mercury
is being close to being so. Note that Saturn, which is quite oblate,
has an ellipticity equal to 0.09796. So, it wouldn't be surprising if
Mercury's ellipticity is measured to be zero within experimental error.
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QUESTION:
Can the Hellas Basin crater on Mars be viewed from the Earth? What size
telescope would you need?
ANSWER from Roger Herzler
on 13 January 2006:
Several features on Mars are visible in a backyard telescope. For example,
the snow caps are visible in a 4" telescope.
I was able to find some good pictures
of the Hellas Basin, which is an impact crater:
Univ. of Texas:
http://www.tsgc.utexas.edu/everything/mars/hellas_basin.html
Imagiverse's own column on it:
http://www.imagiverse.org/activities/robotics/iro/aaron.htm
NASA website including details on it:
http://rst.gsfc.nasa.gov/Sect19/Sect19_12.html
and this Wikipedia entry:
http://en.wikipedia.org/wiki/Hellas_Planitia
According to Wikipedia, it was observed
in the 1800s from Earth, and it wasn't uncommon for astronomers to
be using 6-10" telescopes during that period. My suspicion
is that would be sufficient, but I've not viewed it personally and
can't find a direct answer to "What size telescope would you
need?"
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QUESTION:
How can we imagine a universe without human beings?
ANSWER from Stephanie
Wong on 3 January 2006:
This question is quite a feat to answer, since if there were no human beings,
no humans would exist to imagine a universe without human beings! :-D
When you think about something as grand
as the universe, though, we humans are miniscule things, residing
on quite a small speck of rock in the sky. Consider this image
on Astronomy Picture of the Day: http://antwrp.gsfc.nasa.gov/apod/ap060101.html
and then look at this "Family Portrait":
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-solarsystem.html
I hope this is a start for you to ponder
your personal answer to this question.
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QUESTION:
How would I draw a sketch of the relation between the Sun, Earth, and Moon and
then explain how do they move and on what timescale?
ANSWER from Roger Herzler
on 1 October 2005:
This is raw opinion. If
you're doing this for an assignment you should ask your teacher
if this is acceptable.
I believe that the best way to illustrate
this type of relationship is to draw up a view from the "top
down". That is, looking down from above you can see the
circular orbital paths that both the Earth-Moon and the Sun-Earth
make. If you needed to show how they move you could show rough
estimates based upon how long they take to orbit a body (Moon and
Earth) or maybe how long it takes for the Sun to complete one turn
on its axis (~25.4 days).
For example, if you drew out a circle
representing the Earth's orbit around the Sun, and placed 4 "Earths" on
the circle - one for each equinox, you'd be able to illustrate that
the Earth travels around the Sun. You could label each Earth
for the season its experiencing such as Fall, Winter, Summer and
Spring. It would form roughly an X if you drew a line between
each of those seasonal Earths, with the Sun in the center.
A similar orbit diagram could be sketched
out to show the Moon's orbit around the Earth, which occurs once
about every 28 days.
Here's a decent orbital diagram that should
help you get started on what it looks like:
http://www.nineplanets.org/overview.html
OR
http://ssd.jpl.nasa.gov/orbits_inner.html
(ignore the yellow asteroid belt)
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QUESTION:
Last evening (Sept. 22) at sunset, I saw an incredible streak of light across
the sky. It looked like some sort of rocket launch. Can you tell
me what it was?
ANSWER from Roger Herzler
on 23 September 2005:
Do you live in California or a neighboring state like Arizona? If so,
you did see a rocket last night putting a satellite into orbit. It was
launched from Vandenberg Air Force Base. I saw it as well and it was
stunningly beautiful. You can find more news about it here:
News Story:
http://www.signonsandiego.com/news/state/20050922-1958-ca-rocketlaunch.html
Vandenberg Launch Schedule:
http://www.spacearchive.info/
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QUESTION:
Please explain how it has been proved that the Earth revolves around the Sun
once a year instead of the constellations traveling around the stationary
Earth.
ANSWER from Roger Herzler
on 27 September 2005:
Great question! Is the answer "because Kepler said it was so" good
enough? :o)
Actually, the answer can be found on this
link:
http://curious.astro.cornell.edu/question.php?number=190
That link states that it's been proven
in three different ways: "aberration (slight change in stellar
positions due to Earth's speed), parallax (slight change in stellar
positions due to Earth's changing position) and Doppler effect (slight
change in color of stars due to Earth's speed)."
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QUESTION:
Why isn't Sirius considered part of the solar system?
ANSWER from Stephanie
Wong on 26 September 2005:
For something to be inside the solar system, it has to be within the sun's
heliosphere (i.e. within the "heliopause"). The heliopause
is the boundary between the solar system and what we call interstellar space. At
the heliopause, the the sun's solar wind can no more push back the intestellar
medium of interstellar space. Sirius, which is a star over 8 light years
away from the sun, is considerably outside the sun's magnetic bubble. Therefore,
it is not a part of the solar system, even though it is the brightest star
in the sky.
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QUESTION:
Is it true that Phil Plait's Bad Astronomy website has been taken over by that
other guy who makes up ridiculous claims about space exploration (such as
trying to convince people that faces on Mars are other than optical illusions)?
ANSWER from Michelle Mock
on 9 September 2005:
BadAstronomy.com is
not to be confused with other sites using similar spelling attempting
to purposely mislead the reader. There are certain individuals
in cyberspace who purposely create 'educational' websites intended
to provide blatantly false information to anyone gullible enough
to believe it. Be careful of what you read online. Just
because you see it in print does not make it true.
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