h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is not a challenge to write an entry. It is a challenge to write a paragraph or two.

The Parsecs entry A201754 defines a parsec in terms of parallax, but it completely skips over any explanation of parallax. It needs a couple of paragraphs explaining what parallax is all about. There's even a handy diagram already attached to the entry, so it shouldn't be too difficult to explain.

I could do it myself but I haven't the time at the moment. So if any person who understands parallax would like to write an explanation, just post the paragraphs here and I will add them to the entry when I get a chance.

Hold a finger up in front of you and close one eye. Now close it and look at your finger with the other one. As you can see, the position of your finger has moved relative to its background. Trigonometry can determine from the point half-way between your eyes and the point halfway between the observed positions of your finger, what the angle would be if either viewpoint formed a triangle. This would be its parallax.

In measurement of stellar parallax, the left and right eyes are observations of a star from Earth six months apart, either side of the Sun. For a star to have a parallax of one arcsecond, the angle would represent 1/60th of an arcminute, which would itself represent 1/60th of a degree; a degree being 1/360th of the circle of the whole sky. Thus an arcsecond represents 1/1,296,000th of the circle.

How's that?

Thanks, Christopher. I've paraphrase what you said slightly, put it into the Entry with some new headers and added you as an author of the Entry.

WHat do you think of it? A201754

Looks great Just one missing bit -

>>Most of know that angles are measured in degrees

is missing an us.

Thanks.

So now you have one Edited Entry credited to your name. It doesn't seem to have shown up on your personal space yet, but I'm sure it will soon.

No biggie. It's one of 3, over 3 different accounts, in 9 years. Hardly of gnomonic import.

Oops!

>>Hold a finger up in front of you and close one eye. Now close it and look at your finger with the other one.

You can't close it twice!

OK, I've reworded it again. What do you think?

Great