Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: telling time by the stars (was: astronomy activity help)



"Robert W. Arts" wrote:
...
middle school students (grades 5 - 8)
... looking for an astronomy activity

1) Bernard C. just posted some suggestions that sound good,
especially for the more advanced students.

2) Here's an idea. (It's not guaranteed to be a good idea,
since I have no experience actually teaching it, but it
sounds good.) It ought to be doable for the younger ones.

Teach 'em to tell time by the stars.

If you do it right, this can be educational. It teaches
the kids a few things about the constellations, and it
teaches 'em a few things about spherical geometry.

Telling time is a lot harder than most people think. I just
checked with google and found a googol of sites that describe
what I call the "standard hokey" technique -- namely the one
that depends 100% on the "pointer" stars: Dubhe and Merak
(Alpha and Beta Ursae Majoris). This has the slight problem
that it doesn't work.

It works OK at, say, 10PM in late April, when the pointers
are high overhead, but it gives the wrong answer 3 months
later and/or 6 hours later (because of spherical geometry)
and it gives no answer at all 6 months and/or 12 hours later
(because you'll have trouble seeing the pointers).

Note that typical charts of the circumpolar stars use a
polar projection, which doesn't give a very good portrayal
of how things actually look. Suppose you are standing at
lattitude 40 degrees North, and the 0-hour circle (marked
by e.g. Beta Cassiopeiae) is overhead. That does _not_
mean that the 18-hour circle (marked by e.g. Gamma Draconis)
is a horizontal line 40 degrees above the horizon. It
runs horizontally through the pole, but then it dips
quite markedly. After all, if you extend the 18-hour
circle 2x farther in that direction, it dives through the
western horizon.

I've found several on-line star-chart generation sites that
get this wrong, but I've been unable to find one that gets
it right. Can anybody recommend something that works?

Anyway: Here is a writeup on how I tell time by the stars.
It's not very detailed, but it should get you started in
the right direction.
http://www.monmouth.com/~jsd/physics/star-time.htm