Re: m34, double cluster

On Jan 27, 4:56 pm, brucegooglegroups <brucegooglegro...@xxxxxxxxxxx>
wrote:

Facing northwest, which way would I pan my binoculars from Algol to
m34; from Eta in Perseus to the Double Cluster?

Brian probably gave you the answer (local, time dependent, left-right
and up-down directions) you wanted.

I'll now encourage you to learn to use 'astronomical' directions:

In astronomy, north is the direction toward the north celestial pole
(in general, toward Polaris is close enough). South is of course the
opposite direction. East and west are perpendicular to any given
north-south line. West is the direction toward which celestial
objects appear to move or drift due to the earth's rotation.

Thus, independent of the observer's location and independent of the
time of year, M34 is west-northwest of Algol. Similarly, the double
cluster is west-northwest of Eta Persei. These directions will remain
correct at any time for any date (neglecting the slow, long-term
changes due to precession). Brian's directions (as Brian is well
aware) will not be correct for different times on the same date nor
for the same times on different dates.

Often in books and magazines these (astronomical north, west, etc.)
directions are used for star-hops, etc. Thus they're useful to know
when reading as well as when giving your own observing reports or when
explaining to others where one celestial object is relative to another
in a non-ambiguous manner.

When using a telescope I find it easy to keep track of the
astronomical directions. Without a clock drive running, the direction
toward which celestial objects appear to drift in the telescopic field
of view is west. After thus determining west and east, I nudge the
telescope tube toward Polaris. The direction (perpendicular to the
previously determined west-east line) from which 'new' stars appear to
enter the field (when nudging the telescope toward Polaris) is north.
The opposite direction is of course south.

It's best to repeat the above direction determination procedure each
time one wants to know the directions within one's telescopic field of
view. Sometimes north will be up. Sometimes north will be to the
right. Sometimes north will be down, and sometimes north will be to
the left. Similarly for the other directions. But if one celestial
object is north of another, it will (neglecting precession) always be
north of the other regardless of the date or time.

When using a star atlas, north is the direction of increasing
declination, generally 'up' - the direction toward the north celestial
pole. West is the direction of decreasing RA, generally to the
'right'.

Bill Greer
To sketch is to see.
.

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