Stupid Observing Trick

David Copperfield (the illusionist, *not* the Charles Dickens character)
is known for such stunts as making the Statue of Liberty disappear. You
can upstage him for a short while this week: The solar system's most
massive planet, Jupiter, can be made to vanish with a mere -- though
measuredly deliberate -- glance of your eye!

Here's how to do it:

1. Over the next couple days, step outside during late dusk or early
evening; locate Venus and Jupiter, both gleaming low in the
western sky.

2. Stare directly at Venus, then tilt your head so that an imaginary
line connecting your eyes is roughly parallel with a line defined
by Venus and Jupiter.

3. Now utter the magic incantation: "Oh, great Jove, swirling orb of
hydrogen and methane -- begone!" (If pinched for time, this step
may be skipped with no loss of effectiveness, though you won't earn
as many style points...)

4. Cover (or close) your *right* eye. Poof! -- Jupiter will disappear
from your left eye's field of view, so long as your gaze stays
fixed on Venus and your head maintains the required tilt.


This trick is nothing more than a celestial analog of the ol' two-dots-
on-paper blind-spot demonstration, of course. The fovea (the central
region of the retina) and blind spot are some 17 degrees apart. Likewise
the separation of Venus and Jupiter for a short spell early this week,
hence the stunt's restricted time period.

I've wondered whether there might be a practical observational use for
knowing the location of my blind spot. For instance, when trying to
detect a faint fuzzy in my telescope's field of view, which happens also
to contain an annoyingly bright and distracting star, might it be feasible
to fudge the magnification, the centering, or my head's orientation to
position that bright star onto my blind spot, effectively squelching it
from view?

Then again, perhaps the reason why this idea hasn't been exploited is
because of a far simpler alternative: If you've got an annoyingly bright
star in the field of view, then move the telescope a smidgen to position
that offending star just outside the FoV!

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Mark Gingrich San Leandro, California