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Caption: "Lunar perigee and
apogee apparent
size comparison (from
2007
April and
October
2007, when events occurred near full-phases)."
(Slightly edited.)
Features:
- In this comparison, the Moon's
angular diameters
at perigee and
apogee
are have their correct relative apparent size.
Recall that in astro-jargon,
"apparent" means as seen from Earth.
- On the sky,
the difference in the angular diameters
is just a bit too small to be seen by the unaided
naked eye.
However, it is easily measured with simple instruments.
- Note that the images at
perigee and
apogee both
show full moons.
In fact, only occasionally does either
apsis (pl. apsides) coincide with
a full moon.
To explicate: the
mean anomalistic month = 27.554549878 days (J2000) is the
mean period between like apsides, but
mean lunar month = 29.530588861 days (J2000).
So there is a fairly long interval before
an apsis
and full moon
cycle back into concidence after a given coincidence.
Astronomical perturbations
account for the fact that the
mean anomalistic month = 27.554549878 days (J2000)
and the
mean lunar sidereal month 27.321661547 days (J2000) ≅ 27.32166 days (to 7 digits) ≅ 27.3 days
(the true
orbital period
relative to the
observable universe)
are NOT the same.
- By the by,
a supermoon is
a near-perigee
occurrence of a full moon
or new moon---but
"supermoon" is just phony modern made-up term.
Credit/Permission: ©
Tom Ruen (AKA User:Tomruen),
2007
(uploaded to Wikipedia by
User:User:File Upload Bot (Magnus Manske),
2009) /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Lunar perigee apogee.png.
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File: Moon file:
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