Astrophotography by Anthony Ayiomamitis

Lunar Image Gallery - Scenic Phenomenon

A common misconception is that the moon is larger when it is near the horizon than when it is high overhead. However, this optical illusion is not true, for the apparent size of the moon is virtually the same when it is rising or setting near the horizon or when viewed overhead (in fact, it is very slightly smaller when viewed near the horizon due to refraction as well as the greater added distance in observing across the earth's radius). This illusion has been wrongly attributed to landmarks near the horizon, such as homes and trees, supposedly giving a sense of perspective and whereas the same perspective is lost when looking at the overhead moon bathed in an empty sky. As noted by Donald E. Simanek and Carl J. Wenning, the real reason behind this trick by our brain is the perception of the moon being against a "close" or "distant" foreground and which is lucidly described by the above two references.

In contrast, it is puzzling that when a physical change in the apparent size of the moon does occur, due to its elliptical orbit around our planet, the change in the apparent diameter which can be up to 14% between apogee and perigee, is not noticed at all. In fact, the change in the apparent diameter of the moon is a monthly phenomenon and is something that could be discerned quite easily during any given lunation by looking very carefully at the full moon and the waning crescent thirteen days later (or observing a waxing crescent thirteen days earlier)!

At apogee, the moon is approximately 406,500 km away from earth with an apparent diameter of about 29.5' whereas, at perigee, it is approximately 356,500 km away and is characterized with an apparent diameter of about 33.6'. This difference of 50,000 km between apogee and perigee leads to the dramatic change in the apparent diameter as illustrated by the two full moons below which were strategically selected during 2006 so as to have the full moon as near to its minimum possible perigee and maximum possible apogee as possible when crossing the local meridian.

Furthermore, the perigee full moon below, captured during late summer, was slightly tinted in colour when crossing the southern meridian due to its relatively low altitude during each summer and in contrast to the sun when the latter is at its highest during the same season. These relative positions between the sun and the moon are juxtaposed six months later and during mid-winter with the (apogee) moon at a much higher altitude relative to six months earlier (note the absence of tinted coloration due to atmospheric effects and sharper image) as well as relative to the sun. The sun is now also much lower in the sky as compared to six months earlier (see here).

Note: The change in the apparent diameter of the sun due to perihelion and aphelion is fully documented elsewhere on this website (see here).


Image Details
Full Moon at Apogee and Perigee
Imaging Details
Body:
Moon

Mass:
0.0123 x Earth

Mean Eq Diameter:
0.2719 x Earth

Distance:
357,210 - 405,978 km

Sidereal Rev:
27d 07h 43m 11s

Age:
Apo 14d 12h 50m
Peri14d 22h 49m

Phase:
Apo 99.8%
Peri100.0%

Diameter:
Apo 29.87 '
Peri33.89 '

Magnitude:
-12.7

Rukl:
N/A
Date:
Feb   13, 2006 (00:32:00 UT+2)
Sep   08, 2006 (01:31:00 UT+3)

Location:
Athens, Greece
(38.2997 N, 23.7430 E)


Equipment:
AP 160/f7.5 StarFire EDF
AP 1200GTO GEM
Canon EOS 300d


Exposures:
1 x 1/320 sec   (Apogee)
1 x 1/320 sec   (Perigee)
ISO 100/400
JPG Fine Image Format
3072x2048 Image Size
Manual Mode


Software:
Canon FileViewer V1.3.2
Photoshop CS2


Processing:
Unsharp Masking
Resampling (20%)
Layers & Masks
JPG Compression