Pi

Astronomy Questions & Answers

How many digits are satisfactory in the measurement of pi?

In the 3rd century BC, Archimedes proved that the ratio of a circle’s circumference to its diameter is less than 3 1/7 but larger than 3 10/71. That’s about 3.141. Later mathematicians have computed what we now call p (pi) to greater and greater accuracy — but how many digits…

Hobby-based Q&A

How can we find the Sun's place among the constellations?

How can I find out how our Sun would look among the constellations, as seen from a nearby star? What made me curious was a painting by space artist David Hardy that pictured the Sun as an extra star in Cassiopeia. Fancy planetarium projectors produce such scenes, but you can…

Parallax

Astronomy Questions & Answers

Should you use light-years or parsecs for astronomical distance?

You give astronomical distances beyond the solar system in light-years, but professional astronomy papers use parsecs. Which is preferable? Light-years, no question! Here’s how I see it. The parsec (which equals 3.26 light-years) is defined as the distance at which a star will show an annual parallax of one arcsecond.…

Astronomy Questions & Answers

When we say a galaxy is 300 million light-years away is that its distance now or 300 million years ago?

When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago? Oftentimes, neither! In most cases astronomers try to get a handle on a galaxy’s distance by measuring its redshift: the degree to which the universe’s expansion has stretched its light…

NGC 4889

Astronomy Questions & Answers

What's the most distant object I can see with my telescope?

Is there a more distant object than NGC 4889 (Caldwell 35) that I can see with my 5-inch reflector? Yes, by a factor of 7! Think quasars. NGC 4889 is a member of the Coma Galaxy Cluster, which lies about 300 million light-years away. But the quasar 3C 273 is…

Stand-out star on the rise in December

Science-based Q&A

Why are the stars so far away?

Why are the stars so far away? That question has a real answer: Because if the stars were much closer, Earth wouldn’t exist, and we wouldn’t be here to ask.

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