Florian wrote:

I suppose you could also make Venus vanish if you covered your
left eye. ;-)

Yes, that also works, but I think causing the more massive -- by a
factor of nearly 400 -- planet to vanish is a flashier stunt.

And once you've mastered the art of making planets disappear, you can
then test your prowess on still larger objects -- stars. Two meeting the
angular-separation criterion are Sirius and 2nd-magnitude Saiph. (Saiph
being Kappa Orionis, the hunter's right kneecap; I unabashedly suggest
the name "knee-kappa" as a corny mnemonic aid...)

Step 1. With both Sirius and Orion well above the horizon, tilt your
head so that a line connecting your eyes is roughly parallel
with the line between Sirius and Kappa Orionis.

Step 2. Now stare intently at Kappa.

Step 3. To those well north of the equator (for whom Orion appears "right
side up"), cover your right eye; to observers well south of the
equator (for whom Orion appears "upside down"), cover your left
eye. Sirius will then vanish from view -- an averted view, mind
you -- so long as you maintain the proper head tilt and keep
fixated on Kappa.


At this time of year you must go out under the pre-dawn sky to view
Sirius and Kappa Orionis. However, the two don't shift their relative
positions noticeably over our lifetimes, which makes them a fine pair for
this stunt whenever fast-moving planets don't cut it, angular-wise.

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Mark Gingrich San Leandro, California