Lunar eclipse Melbourne August 2007 - turquoise moon
phase due to light refracting through earth's ionosphere to reach the moon
instead of through the stratosphere which gives the red/orange phase.
crop & resized for web - Canon 1D Mark III 1600ISO, 1/3rd
sec f/5.6 500mm Mak-Cassegrain, MF using live preview LCD screen on sunlit part
(umbral part not visible on LCD screen at f/5.6)
Lunar eclipse May 2004 with a Canon S30 afocal method.
Some stats about the moon:
composition of surface rocks:
mainly basaltic igneous in character
exceptionally high concentrations of titanium, scandium, zirconium
& soil is enriched in volatile elements as well as copper, silver,
gold.
isotopic analysis suggests the moon rocks are almost 5 billion years
old.
diameter is 3480km (cw earth 12,760km)
average distance from earth is 379898km
thus its angular diameter as seen from earth is about 0.5°
earth's mass is 81.5 times that of the moon
sidereal period is 27.32 days
synodic period (full moon to full moon) is ~29.5 days
rotates on its axis once every 27d 7h 43m on average which is the same
as its sidereal period
this is why we never see its "dark side" - see tides
for the explanation of why this is so!
actually, as the moon's orbit is elliptical, it moves more rapidly
when nearest the earth & more slowly further away in accordance
with Kepler's 2nd law. As a result, rotation on its axis &
revolution around earth coincide only on the average, at times we
can see a little more on its eastern side and at other times we can
see a little bit more on its western side, this apparent shifting of
the moon is called libration &
because of it, we are able to see about 5/9ths of its surface, not
just half.
this is also why, if you were standing on the moon:
Earth would always appear to be in the approximately same position in the sky,
the Earth never sets or rises when seen from most parts of the moon.
however, libration changes the horizontal position of Earth by
a few degrees while in the vertical direction the Earth moves at
least +-5 degrees (this is the inclination of the lunar orbit to
the ecliptic), so for most part of the Moon the Earth is in the
sky or is not, but there is quite a wide band around the
terminator where the Moon hovers close to the horizon setting
and rising about once a month.
you would see earth rotating on its axis
you would still see a sunset and sunrise but these would occur
once each every 29.5 days as each day would take almost 15 earth
days and each night the same duration.
its lack of appreciable atmosphere means:
it has extremes of temperatures on its surface:
it is gets very cold during the prolonged "night",
dropping to minus 150degC
it gets hot during the prolonged day with the sun at is zenith,
reaching more than 100degC
but below 6" of surface, its temperature varies little,
staying not far from the freezing point of water
it is pockmarked with craters due to meteor impacts:
you can actually see these happening - see meteors
there are some 4,000 with diameters greater than 10km, 60,000 with
diameters > 1km, 40 million with diameters greater than 100m and
400 trillion with diameters greater than 10cm
it does not get colorful sunsets or sunrises and the lunar sky is
completely black
photographing the moon to achieve good resolution of the craters requires:
adequate magnification:
you will need a focal length of at least 600mm in 35mm terms to get
reasonable filling of your photograph
image diameter of an object in mm = actual focal length of lens
(in mm) x subject size / subject distance
for 35mm film, percent of its height (24mm) taken by the subject =
image diameter of an object in mm x 100 / 24
thus for the moon, with average diameter 3474km at distance
379898km, for a 1000mm lens, image size will be 9.1mm, and thus on
35mm film will occupy 9.1/24 = 38% of the film height
the moon will fill 1% of your image height for every 30mm focal
length (in 35mm effective terms), thus:
a 900mm effective lens will fill 900/30 = 30%
a 300mm actual focal length on a 2x cropped sensor Olympus
gives 600mm effective = 600/30 = 20%
thus there are 2 main approaches to achieving near 100% image
size of the moon:
eg. Olympus dSLR with 10" f/5.6 Newtonian telescope
and 2x teleconverter => effective f.l 2845mm = 95%
afocal method
with a point & shoot digital or webcam with telescope and
eyepiece
eg. my astrophotography
using a Canon S30 point and shoot on a 10" f/5.6
Newtonian telescope.
NB. effective f/ratio, focal length and projection
magnification can be calculated see afocal
method.
minimise camera shake:
use a tripod or mount to a telescope
take a look at the Moon with your setup and tap the
lens. If the image bounces several seconds, you will need to be extra
careful in taking images (wait for the bouncing to stop and use mirror
lock).
use fastest shutter speed possible if at high magnifications:
with stationary tripod, 1/6 s is maximum for 600mm lens focal length, so stay
shorter than 1/20s at least in the beginning.
use a remote shutter or a self-timer
if using an SLR, use mirror lock. If no mirror lock is
available, you need to get a very solid tripod.
avoid windy nights
correct exposure:
don't use auto-exposure as likely to over-expose, consider the sunny
16 rule:
f/16 and 1/(ISO)th sec ie. f/16, 1/100thsec at ISO 100 = f/8,
1/400th sec at ISO 100.
bracket exposures especially if different phases or moon getting
closer to horizon (see atmospheric
extinction) to get the shortest exposure time that exposes the
moon past
half histogram on digital cameras.
lunar eclipse:
totality:
this is hard without good equipment as you need a
combination of focal length (eg. 600-1200mm), fast aperture
(eg. f/4-5.6), high ISO to allow reasonable fast shutter
speeds to minimise movement (eg. 1-2sec) and preferably have
tracking on a motor driven mount.
mirror lock and self timer is useful to minimise camera
shake.
ISO 3200, 2secs at f/5.6 thus ideally need a faster lens
eg. 600mm f/4 to allow 1sec
or some stack 5 images at ISO 400, f/5, 0.5sec
you could use a 200mm f/2.8 on a 1.6x crop camera using
ISO 400, f/2.8, 1sec
turquoise phase:
this is much easier to do as you can do this on a
photographic tripod without tracking and you can manually
focus using a live preview LCD on a dSLR.
eg. 500mm f/5.6 on APS-H = 650mm f/5.6 at 1600ISO, 1/3rd
sec
see my photo at top of page.
eg. 300mm f/4 with 1.4xTC on APS-C = 670mm equiv. f/5.6 at
ISO 800, 1/3rd sec but 1 stop underexp.
aiming for maximum sharpness, resolution with minimal aberrations:
focus carefully and iterate until perfect - if autofocus works, use
it.
live preview may not work as cameras tend to over-expose moon on
live preview, focus on a bright star instead.
live preview will generally not work during a total lunar eclipse
phase as the moon is too dim
stop down the aperture 1-2 stops to improve the image quality,
especially if using teleconverters or legacy lenses.
use lowest ISO possible although 400ISO on a dSLR would be reasonable
you will need at least 80mm diameter aperture to achieve satisfactory
resolution, a 200mm f/4 camera lens won't be adequate, even with
teleconverters, but a 200mm f/2.8 with 3x teleconverter will be
reasonable.
always take several batches of images, with refocusing in between.
Atmospheric seeing changes the conditions constantly - you need to pick
the sharpest image for processing.
for image sharpness, image when the Moon is high up - fewer atmospheric effects.
for even sharper results, learn to process - and consider buying ImagesPlus.
Photoshop cannot compete with the way iterative restoration in
ImagesPlus which works magic for lunar images. Some use 100 iterations,
Gaussian, 5x5. But this definitely depends on the optics used -
change of magnification as well as quality of optics changes what are
the most optimal parameters.
as in the saying "once in a blue moon" to indicate the rarity of
an occurrence
well it now has two definitions:
the traditional definition:
according to Canadian folklorist Philip Hiscock, the term
"blue Moon" has been around for more than 400 years and
signified the 3rd full moon in a 3 month season having 4 full moons
the erroneous but adopted definition since a Sky & Telescope
article in 1946:
the 2nd full moon in within the same month
It is rare to have two full Moons in a single month. The
reason is simple: the average time between full Moons is 29½ days.
Thus February, with at most 29 days, can never accommodate two full
Moons. To squeeze a pair into a month with 30 days, the first must
occur on the 1st of the month. Months with 31 days, including July,
can have two full Moons only if the first one occurs by the 2nd of
the month, as happens in July 2004. The last time a calendar month
included two full Moons was November 2001. Not until May 2007 (in
North American time zones) or June 2007 (Europe) will it happen
again.
In fact, the very earliest uses of the term were remarkably like
saying the Moon is made of green cheese. Both were obvious absurdities,
about which there could be no doubt. "He would argue the Moon was
blue" was taken by the average person of the 16th century as we
take "He'd argue that black is white."
The concept that a blue Moon was absurd (the first meaning) led
eventually to a second meaning, that of "never." The statement
"I'll marry you, m'lady, when the Moon is blue!" would not
have been taken as a betrothal in the 18th century.
But there are also historical examples of the Moon actually turning
blue. That's the third meaning — the Moon appearing blue in the sky.
When the Indonesian volcano Krakatoa exploded in 1883, its dust turned
sunsets green and the Moon blue all around the world for the best part
of two years. In 1927, the Indian monsoons were late arriving and the
extra-long dry season blew up enough dust for a blue Moon. And Moons in
northeastern North America turned blue in 1951 when huge forest fires in
western Canada threw smoke particles up into the sky.
So, by the mid-19th century, it was clear that visibly blue Moons,
though rare, did happen from time to time — whence the phrase
"once in a blue Moon." It meant then exactly what it means
today, a fairly infrequent event, not quite regular enough to pinpoint.
That's meaning number four, and today it is still the main one.
But meaning is a slippery substance, and I know of a half dozen songs
that use "blue Moon" as a symbol of sadness and loneliness.
The poor crooner's Moon often turns to gold when he gets his love at the
end of the song. That's meaning number five: check your old Elvis
Presley or Bill Monroe records for more information.
And did I mention a slinky blue liquid in a cocktail glass, one that
requires curaçao, gin, and perhaps a twist of lemon? That's number six.
