The Moon |
The
wind was a torrent of darkness among the gusty trees, The moon was a ghostly galleon tossed upon cloudy seas, The road was a ribbon of moonlight, over the purple moor, And the highwayman came riding- Riding-riding- The highwayman came riding, up to the old inn-door. |
Our
moon is a big round lump of rock, and it goes anticlockwise round and
round the earth about 238,857 miles away, appearing to follow the nearly
same path across the fixed stars and constellations as the sun, and
all the planets. In fact, the path the moon takes is angled
at 5 degrees to the Ecliptic (the path that the Sun takes)
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The
moon used to spin quite fast on its axis, but now it has slowed down,
and we always see the same side of it because it takes the same time
to turn around itself as it takes to go around the earth. One day the
earth will itself stop spinning, and will have the same side always
turned to the sun. This will mean that all those people who bought holiday
homes in the wrong hemisphere will not be able to get insurance, but
we don't need to worry about that for a few years yet.
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It
takes 27 days and 8 hours for the moon to complete an orbit of the earth.
However by the time it gets back to the same place, the earth has gone
a bit further around the sun on its yearly orbit. This means that from
New Moon to New
Moon, (or Change to Change), it takes 29 days, 12 hours and
44 minutes, which is near enough 30 days.
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So
what do we see in the Corvedale? Well lets start at a Change
(or New Moon). You can't see the moon, why?, because it is next to the
sun, and crosses the sky in the daytime. It usually crosses above or
below the sun, but occasionally it crosses in front, and then we get....a
Solar Eclipse....In fact there are
two solar eclipses per year around the world in March and September,
but they aren't often visible in the Corvedale - it might be the wrong
time of day or wrong latitude.
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What
then? Well as the moon moves leftwards against the background of the
fixed stars at the speed of 12 degrees a day (a fist and a finger),
we start to see the D shape appearing. It is now Waxing,
in its Separation, and sailors used
to say it was Abaft the Sun, i.e.
it follows it across the sky during the day. By about day seven, it
is at right angles to the sun, rising in the east about midday, and
setting in the west at midnight.
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On day 15, it is now Full, rises at sunset, sets at sunrise, and is directly opposite the sun, reflecting a lot of the suns rays back onto the earth in the form of Moonlight. |
It
now begins its Waning, is in its
Application, and is said to be Afore
the Sun. It rises later and later, consequently setting earlier,
and by day 23 is rising at midnight, setting at midday, and looks like
a C. Then,
before you know it, we are back to Change, or New Moon on day
30.
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In
the same way as the sun is high in the sky in the summer, and low in
the winter, the Full Moon is directly opposite, so it is high in the
winter, and low in the summer. Thats why snowy landscapes at full moon
are so bright. And at full moon we can get...a Lunar
Eclipse... which again happen
twice a year, and occur when the full moon moves into the shadow of
the earth. It can be quite dramatic, the full moon will turn blood red
as the earth's atmosphere distorts the light, wolves howl, clocks strike
thirteen etc etc.
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You can predict how old the moon will be on any particular date .............e.g. 25th December 2005
Take
the year
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(2005) |
and
add 1(unless its Jan or Feb when you don't)
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(2005 + 1 = 2006) |
Divide
by 19 (the cycle of the moon) and see what is left over
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(2006 / 19=105 and 11 remaining) |
Multiply
by 11 (the number of extra days in a solar year compared with a lunar
year)
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(11 x 11 = 121) |
Divide
by 30 (days in the lunar month ) and see what is left over
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(121 / 30 = 4 and 1 remaining)) |
Add
this to the number of months since March, inclusive, and the day of
the month
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(1 + 10 + 25 = 36) |
Take
away 11(this system was worked out in 1594, and we've lost 11 days since
then in 1752)
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(36 - 11 = 25) |
You
may need to add or subtract 30 to make the result come between 1 and
30
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(No need this time) |
30
is New moon, 15 is Full moon. This method still seems to work, 400 years
after it was described here.
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(Day 25 is 5 days before New Moon) |
How light is it ? |
A lunar 'day' lasts 30 of our 'earth' days (29 days, 12 hrs 44 mins), and is divided into 15 days of light, and 15 days of darkness, which would make living there a bit trying. Unromantically, there is no such thing as 'The Dark Side of the Moon' because every point gets the same amount of light, near enough. |
Looking at the moon
Our
moon is good in binoculars, both
in the daytime (stay away from the sun) and at night. Surprisingly,
full moon isn't the best time to look at it (the detail is lost as there
are no shadows). Sadly you won't see any spacejunk or American flags,
but its quite fun to identify the craters, the mountain ranges, the
so-called seas, and any passing Clangers. You can buy a map of the moon
here. And here is more
info on the moon. And here is a video,
shot from a space craft flying round it.
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