Monthly Archives: September 2012

How Big Must a Black Hole be to Tear Apart a Star?

Question:  What should the critical mass of a black hole be in order for the star to be torn apart? How does one find this critical mass?  — Safar Answer:  The general answer to your question depends upon a number … Continue reading

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Turn an Old Satellite Dish into a Radio Telescope

Question:  I have a old satellite dish in the yard [that I] wanted to use for radio astronomy for the kids.  It is 10ft [in diameter.  How can I make it observe astronomical objects?]  — Bill Answer:  In fact, you … Continue reading

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How Do Astronomers Measure the Size of the Universe?

Question: I’m 15 years old. I want to know how do scientists measure the size of universe or observable universe.  — Hassan Answer:  There are several techniques that astronomers use to measure distances in the Universe.  Most of these distance … Continue reading

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Velocity Reference Frames Used in Radio Astronomy

Question:  I have read that radio astronomers are able to detect velocities in the objects they study and report these as V_LSR (LSR = local standard of rest).  What are these velocities relative to?  Are they relative to the observer … Continue reading

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Does a Radio Telescope Collect Sound Waves?

Question: I would like to ask two questions.  If a radio telescope works like a radar, and a radar uses microwave radiation to detect the range, speed and other characteristics of remote objects (humans for instance), does radar receive sound … Continue reading

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Relative Sizes of the Earth and the Milky Way Galaxy

Question:  Hi, I just want someone to verify my math –needed to visualize the scale of the galaxy. I found that if the Earth were the size of a grain of salt (0.004 inches) the diameter of the Milky Way … Continue reading

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