When The Moon Was Ours Pdf

[Alexandrin Chaples]

TheMoon is the most recognisable object in the night sky, and has an enormous impact on life here on Earth. But what is the exact distance between the Earth and the Moon? And why is that question not as simple as it sounds? Royal Observatory astronomer Affelia Wibisono explains all...

Light travels at 300,000 kilometres per second, so it takes about 1.3 seconds for light to travel from the Moon back to the Earth. In other words, the Moon is 1.3 light-seconds away from the Earth.

No orbit is perfectly circular. Some are very close, but they are all at least slightly elliptical in shape. Astronomers can measure how near to a perfect circle an orbit is by calculating its 'eccentricity'.

This is expressed by a number that is between 0 and 1. The closer the eccentricity is to 0, the closer the orbit is to a circle. In fact, a circle can be thought of as a special kind of ellipse that has an eccentricity of 0.

The biggest tides occur when the Sun, Moon and Earth align because the gravitational pull of the Sun and Moon combine. Neap tides are smaller and occur when the Sun and Moon are perpendicular to each other. Credit: NASA/Luc Viator/HalloweenNight/Affelia Wibisono.

Since the Moon orbits the Earth and the Earth orbits the Sun, both the Moon and the Earth are the same average distance away from the Sun. On average, the Earth and Moon are about 150 million kilometres (or 93 million miles) from the Sun!

The first spacecraft to attempt to reach the Moon was the Soviet Union's Luna 1 in 1959. Unfortunately, it did not slow down enough to complete its mission, but it did reach the vicinity of the Moon within 34 hours (1 day 10 hours).

Human space travel will usually take longer than robotic ones. On average, the nine crewed missions to the Moon, (including Apollo 8, Apollo 10, Apollo 13 and the six that landed on the surface) took just over 78 hours (3 days 6 hours) to enter lunar orbit. The quickest was Apollo 8 which took 2 days, 21 hours and 8 minutes, while Apollo 17 took the longest with a time of 3 days, 14 hours and 41 minutes (times include the time spent in Earth orbit).

If you were driving at a speed of 40mph it would take approximately 5,791.375 hours to get to the Moon. However, this depends on whether the Moon is in apogee or perigee - and what kind of rocket car you have of course.

The lunar phase cycle takes 29.5 days to complete, and is directly connected to the orbit of the Moon around the Earth. However this is not how long it takes for one orbit to complete. Instead the Moon takes 27.3 days to orbit the Earth once.

This difference comes from how you measure the motions of objects in space. As there are no truly fixed points in space to measure against, you are forced to use objects that are considered not to move to within a reasonable level of uncertainty.

If you measure how the Moon orbits compared to these distant stars you get 27.3 days, the true orbital period of the Moon. However, the phases of the Moon are dependent on how the Moon, Earth and Sun are placed. During the time the Moon orbits the Earth, the Earth has moved on in its orbit around the Sun. In effect, the Moon needs a couple of extra days to catch up and return to the same point in space relative to the Sun. Hence the 29.5 day lunar phase cycle.

You may have noticed that the full Moon always looks about the same. You always see the same pattern of craters, hills, valleys and mare (seas) on the full Moon. In fact if you look at any phase of the Moon, it will always show the same features, though not all of the features will be lit up.

The result is a very slowly rotating Moon: it takes 29.5 days to go from midday to midday on the Moon. Daylight lasts about two weeks and night time another two weeks. That, coupled with the lack of an atmosphere on the Moon, means the temperature changes wildly from over 100C during the day to around -150C at night.

Astronauts from the Apollo 11, 14 and 15 missions and the two Soviet Union rovers, Lunokhod 1 and Lunokhod 2, left a total of five mirrors on the surface of the Moon. Astronomers on Earth can reflect laser beams off these mirrors and record the time it takes for the laser to return. We know how fast the laser beam is travelling (the speed of light) so we can easily calculate the distance that the laser beam has travelled. The Earth-Moon distance would then be half of this value.

The moon, it turns out, is a great place for men. One-sixth gravity must be a lot of fun, and when Armstrong and Aldrin went into their bouncy little dance, like two happy children, it was a moment not only of triumph but of gaiety. The moon, on the other hand, is a poor place for flags. Ours looked stiff and awkward, trying to float on the breeze that does not blow. (There must be a lesson here somewhere.) It is traditional, of course, for explorers to plant the flag, but it struck us, as we watched with awe and admiration and pride, that our two fellows were universal men, not national men, and should have been equipped accordingly. Like every great river and every great sea, the moon belongs to none and belongs to all. It still holds the key to madness, still controls the tides that lap on shores everywhere, still guards the lovers who kiss in every land under no banner but the sky. What a pity that in our moment of triumph we did not forswear the familiar Iwo Jima scene and plant instead a device acceptable to all: a limp white handkerchief, perhaps, symbol of the common cold, which, like the moon, affects us all, unites us all.

Everything became very quiet in the control room as the ghostly figure, white on a white ground, against a dark sky, touched what seemed like white rigging. It all looked like an old, grained, scratchy movie showing some hooded, frost-shrouded early polar explorer standing by the bulwark of an icebound ship.

Then the President made his telephone call to the astronauts, the interchange went off the air, and for a few moments, before the television lights in the White House were extinguished, Mr. Nixon could be seen on the monitor, disengaging, with the help of a technician, a microphone he had had about his neck.

Suddenly, Armstrong emerged with amazing speed from the black shadow of the LM into the brilliant sunlight. There was a sigh from the group; then it fell silent again for a moment. As Armstrong set up the television camera to look back on the LM, conversation resumed.

Finally, at a quarter to midnight, he rose and went into the master bedroom. He returned in a beige jacket, a white shirt, and a blue-figured tie. The Mayor and Mrs. Lindsay, with Davidoff, Gottehrer, Pat Vecchio, and the press secretary, Tom Morgan, squeezed into a black car in front of the Mansion.

A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth (because the Moon is tidally locked with the Earth, the same hemisphere is always facing the Earth). In common usage, the four major phases are the new moon, the first quarter, the full moon and the last quarter; the four minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent. A lunar month is the time between successive recurrences of the same phase: due to the eccentricity of the Moon's orbit, this duration is not perfectly constant but averages about 29.5 days.

The appearance of the Moon (its phase) gradually changes over a lunar month as the relative orbital positions of the Moon around Earth, and Earth around the Sun, shift. The visible side of the Moon is sunlit to varying extents, depending on the position of the Moon in its orbit, with the sunlit portion varying from 0% (at new moon) to nearly 100% (at full moon).[1]

There are four principal (primary, or major) lunar phases: the new moon, first quarter, full moon, and last quarter (also known as third or final quarter), when the Moon's ecliptic longitude is at an angle to the Sun (as viewed from the center of the Earth) of 0, 90, 180, and 270 respectively.[2][a] Each of these phases appears at slightly different times at different locations on Earth, and tabulated times are therefore always geocentric (calculated for the Earth's center).

Between the principal phases are intermediate phases, during which the apparent shape of the illuminated Moon is either crescent or gibbous. On average, the intermediate phases last one-quarter of a synodic month, or 7.38 days.[b]

As seen from Earth, the Moon's eccentric orbit makes it both slightly change its apparent size, and to be seen from slightly different angles. The effect is subtle to the naked eye, from night to night, yet somewhat obvious in time-lapse photography.

When the Sun and Moon are aligned on the same side of the Earth (conjunct), the Moon is "new", and the side of the Moon facing Earth is not illuminated by the Sun. As the Moon waxes (the amount of illuminated surface as seen from Earth increases), the lunar phases progress through the new moon, crescent moon, first-quarter moon, gibbous moon, and full moon phases. The Moon then wanes as it passes through the gibbous moon, third-quarter moon, and crescent moon phases, before returning back to new moon.

The terms old moon and new moon are not interchangeable. The "old moon" is a waning sliver (which eventually becomes undetectable to the naked eye) until the moment it aligns with the Sun and begins to wax, at which point it becomes new again.[4] Half moon is often used to mean the first- and third-quarter moons, while the term quarter refers to the extent of the Moon's cycle around the Earth, not its shape.

When an illuminated hemisphere is viewed from a certain angle, the portion of the illuminated area that is visible will have a two-dimensional shape as defined by the intersection of an ellipse and circle (in which the ellipse's major axis coincides with the circle's diameter). If the half-ellipse is convex with respect to the half-circle, then the shape will be gibbous (bulging outwards),[5] whereas if the half-ellipse is concave with respect to the half-circle, then the shape will be a crescent. When a crescent moon occurs, the phenomenon of earthshine may be apparent, where the night side of the Moon dimly reflects indirect sunlight reflected from Earth.[6]

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