The Moon The second brightest object in the sky, the Moon, has the advantage over the principal brightest, the Sun, in that it can always be looked at directly. The Moon’s diameter is 3,476 kilometres, about one quarter that of Earth. Having no free water on its surface, nor any atmosphere, the Moon has no weather to alter its heavily cratered surface. The lack of atmosphere also causes the Moon`s sky to always be black. The average surface temperatures on the Moon are 107ºC in daylight and –153ºC at night. However, extremes between 123ºC and –233ºC are possible.
Observing the Moon
In observing the Moon, over the course of a year, you notice that full moons do not rise and set in the same positions on the horizon. Summertime full moons rise and set much further to the south than those in winter. This means that summer full moons remain in the sky for a shorter period than those of winter, and reach a lower altitude in the sky. The full moon nearest to midwinter is the highest and longest of the year – the additional light being very convenient for those living in rural areas!
In addition to the seasonal difference, the Moon goes through a cyclic pattern of positions, relating to the horizon, which repeats itself every 18.6 years. This is a cycle of widening and narrowing bands of rising and setting positions. At one extreme point of the cycle (major standstill), the Moon rises and sets far to the north, well beyond the position of the Sun at the summer solstice. Two weeks later the Moon will be rising and setting far to the south, only appearing in the sky for a comparatively short period. During periods of major standstill the Moon, in its various phases, swings between the two extremes.
During the cycle the Moon moves between 28.6º above the celestial equator to 28.6º below. The angular distance (for any object) above or below the equator is known as north or south declination.
2006 was a year of major standstill. With the Moon, reaching both extreme declinations that year, the noticeable effects were the height above the horizon and the points on the horizon (the azimuths) where the Moon rose and set. The most southerly extreme (-28.6º S) was on the 22nd March 2006 when the Moon was above the horizon for just 6.5 hours. The most northerly extreme (+28.6º N) was on the 15th September 2006 when the Moon was above the horizon for more than 17 hours. However, during each month of that year the Moon reached extremes almost as great as the peak months.
Minor standstill In just over nine years after, during minor standstill, the limits of the Moon’s path will have contracted as shown in the second diagram. There will be less of a contrast between the summer and winter full moon positions, though the winter full moon is always in the sky for a much longer period than the summer full moon.
Key positions for the Sun are solstices and equinoxes, whilst for the Moon it is the position of the full Moon closest to the two annual solstices at the time of standstills. These events are best recorded by choosing permanent markers, allowing observers to note positions on the horizon where the Sun or Moon rise and set at the appropriate times. This has long been considered the purpose of most standing stones and stone circles.
Phase chart Like the Earth, the Moon is a sphere which is always half illuminated by the Sun. As the Moon orbits the Earth we see only the part of the Moon that is facing the Sun. These illuminated phases depend on the angular position of both objects relative to each other. During the apparent 29.5 day average lunar orbit around the Earth, the Moon`s lit portion increases as it draws away from the Sun`s position and decreases as it approaches the Sun. In stage 1 of the diagram the Sun has set below Earth`s horizon in the west and the Moon will set shortly afterwards. We see the illuminated portion as a crescent shape. In stages 2 and 4 the Sun is at approximately 90º to the Moon showing illuminated first and last quarters. In stage 3 the Sun is opposite (180º to) the Moon showing a full moon. In stage 6 the Sun and Moon are so close together in the sky (in this case below the horizon) that the Moon is at new moon phase and not illuminated as seen from Earth. At this stage the Sun is behind the Moon, as viewed from Earth, and lights up the opposite side as seen from Earth.
There are eight traditional phases of the Moon. Phase 1 is a new moon, phase 2 is a waxing (increasing) crescent, phase 3 is a first quarter, phase 4 is a waxing gibbous, phase 5 is a full moon, phase 6 is a waning (decreasing) gibbous, phase 7 is a last quarter and phase 8 is a waning crescent.
The new moon rises and sets together with the Sun. During a lunation of 29.5 days, as the Moon passes through a full cycle of phases, it rises roughly 50 minutes later each night. By first quarter it rises around midday and sets around midnight. When it reaches full it will be, more or less, up from sunset to sunrise. By last quarter it will rise about midnight and set at noon before, as it approaches another new moon, its rising and setting times converge again with those of the Sun.
Since the Moon rotates on its axis once per orbit around the Earth, the same side of the Moon always faces the Earth. The Moon completes this orbit once every 27 days, 7 hours, 43 minutes and 11.5 seconds, relative to the stars. The average time between like phases (eg full to full) is 29.5 days, almost 2 days longer than it takes to return amongst the same stars. It moves eastwards by its own diameter approximately every hour. As the Moon always faces the Earth in just about the same position, the Earth remains in approximately the same area of the lunar sky and is not seen to rise or set. Photographs of the Earth rising over the Moon`s surface have been taken from spacecraft.
The Moon revolves around the Earth in an elliptical orbit ranging in distance from 354,000 to 404,000 kilometres. Although we can only see half of the surface, several factors allow us to see a bit further around first one side and then another. Formations on the Moon near the visible edge sometimes come into view and are hidden at other times, so that almost 60% of the surface can be seen from the Earth.
With the advent of telescopes in the 17th century, astronomers discovered features including craters, mountains, faults, rays and domes on the surface. In July 1969 the American Apollo 11 spacecraft carried the first humans, Neil Armstrong and Edwin “Buzz” Aldrin, to set foot on the Moon.
Tides Large bodies of mass in orbit around another mass are warped by proximity to, and gravitational pull on, each other. The Earth has warped the Moon such that it cannot spin on its axis very fast and its near face is bulged towards the Earth. This causes the spin of the Moon to slow down such that one side always points towards the Earth.
Likewise, bulging is produced on the Earth`s crust and its oceans. The Moon produces two tidal bulges on the Earth through the effects of gravitational pull. The height of the tidal bulges is controlled by the Moon’s gravitational force and the Earth’s own gravity pulling the water back. At the location on the Earth closest to the Moon, seawater is drawn toward the Moon. On the opposite side of the Earth, another tidal bulge is produced away from the Moon where the force of its gravity is weakest.
Earth`s tides are also affected by the Sun as the Earth orbits around it. When the Earth, Moon and Sun are in line twice a month at new and full moons, the gravitational pull on the Earth is increased, and high tides are higher than at any other times. Conversely, low tides are at their lowest. These are called spring tides.
When the Sun and the Moon are at 90º to the Earth (during first and last quarter moons), the gravitational pull of the Sun and Moon are competing. At these times, high tides do not rise very high and low tides do not fall very much. These are known as neap tides.
Living on the Mediterranean, you notice that the tides here are very small. Although not the whole storey, the reasons are mostly due to the narrow inlet/outlet to the Atlantic Ocean at the Straights of Gibraltar.
Perigee and Apogee
Lunar Perigee and Apogee Although the Moon has an average distance from Earth of 382,500 kilometres (237,700 miles), it has an egg-shaped orbit around the Earth and so is sometimes approximately 50,000 kilometres closer to Earth than at other times. On average of once a month, the Moon reaches apogee (its furthest from Earth) and about two weeks later it reaches perigee (its closest to Earth). The Moon´s wobbly orbit means that its exact distance at each apogee and perigee varies over the year. Also, the Moon´s phase is different during each apogee and perigee. If the Moon´s phase is at Full during perigee, it looks significantly bigger. If a Full Moon is at apogee it looks smaller.
Looking at the Moon in the sky without anything to compare it to, you may not notice any size difference although it can be significant. The image shows the difference in photographing, with the same lens, a Full Moon at apogee and at perigee.
The apogee and perigee of the Moon have an effect on the tides on Earth. When the Moon is at apogee, the furthest distance from Earth, it has less gravitational pull which, along with other factors that influence the tides, can contribute to lower tides or lower variation in the high/low tide level. When the Moon is at perigee, closer to Earth, there is much more gravitational pull which contributes to the opposite effect of higher tides or greater variation in the high and low tide.
The Islamic calendar is based on lunar months, which begin when the thin waxing crescent Moon is sighted low in the western evening sky just after sunset, a day or close to after new moon.
The twelve months of the Islamic calendar are Muharram, Safar, Rabi’a I, Rabi’a II, Jumada I, Jumada II, Rajab, Sha’ban, Ramadan, Shawwal, Dhu al-Q’adah and Dhu al-Hijjah. On average, twelve lunar months are eleven days shorter than the Gregorian year, which causes the Islamic year to shift earlier, compared to the Gregorian year, by this amount of time.
A tabular Islamic calendar exists for non-religious purposes in which the lengths of the months alternate between 29 and 30 days. In leap years an extra day is added to the last month of Dhu al-Hijjah. The calendar consists of a 30-year cycle in which 11 of the 30 years are leap years. Gregorian dates, corresponding to important Islamic dates, in the tabular calendar are:
Ramadan 2011 – August 1st to 30th August 2011
Islamic New Year 1433 – November 26th 2011
Ramadan 2012 – July 20th to August 18th 2012
Islamic New Year 1434 – November 15th 2012
Ramadan 2013 – July 9th to August 7th 2013
Islamic New Year 1435 – November 5th 2013
Ramadan 2014 – June 28th to July 27th 2014
Islamic New Year 1436 – October 25th 2014
Ramadan 2015 – June 18th to July 17th 2015
Islamic New Year 1437 – October 14th 2015
Ramadan 2016 – June 6th to July 5th 2016
Islamic New Year 1438 – October 2nd 2016
Ramadan 2017 – May 27th to June 25th 2017
Islamic New Year 1439 – September 21st 2017
Ramadan 2018 – May 16th to June 14th 2018
Islamic New Year 1440 – September 11th 2018
Ramadan 2019 – May 6th to June 4th 2019
Islamic New Year 1441 – August 31st 2019
Ramadan 2020 – April 24th to May 23rd 2020
Islamic New Year 1442 – August 21st 2020
The ancient Hebrew calendar was also based on lunar crescent sightings, although the contemporary Hebrew calendar is calculated on a lunisolar basis. The Hebrew calendar has a 19-year cycle of 235 lunar months with an additional lunar month added seven times throughout the cycle. There are many other examples of lunisolar calendars including the traditional 60-year cycle Chinese calendar used to date Chinese New year and mid-autumn festival.
Planting by the Moon is an ancient art, based in folklore and superstition, and backed up by science. Just as the Moon pulls the tides in the oceans, it also pulls upon subtle bodies of water, causing moisture to rise in the earth, encouraging growth. The highest amount of moisture in the soil is at new and full moons and tests have proven that seeds will absorb the most water at the time of full moon.
The theories are:
At new moon the lunar gravity pulls water up, and causes seeds to swell and burst. This factor, coupled with increasing moonlight, creates balanced root and leaf growth. This is the best time for planting above ground crops that produce their seeds outside the fruit. Examples are lettuce, spinach, celery, broccoli, cabbage, cauliflower and grain crops.
During second quarter (waxing gibbous) the gravitational pull is less, but moonlight is strong, creating strong leaf growth. This is generally considered a good time for planting, especially two days before a full moon, the types of crops that produce above ground with seeds formed inside the fruit. Examples are beans, melons, peas, peppers, squash and tomatoes.
After full moon, as the Moon wanes, energy is drawn down. The gravitation pull is high, creating more moisture in the soil, but the moonlight is decreasing, putting energy into the roots. This is a favourable time for planting root crops, including beets, carrots, onions and potatoes. Because of the active root growth, it is also good for planting and transplanting perennials, biennials and bulbs. Pruning is best done in the third quarter (waning gibbous) during mid-October to late November.
In the last quarter there is decreased gravitational pull and moonlight, and this is considered a resting period. This is also the best time to cultivate and harvest, and a generally good time to transplant and prune.
Rudolf Steiner developed biodynamic farming, incorporating the lunar cycle, in the 1920s. Organic and biodynamic farming has grown increasingly popular since that time.
In Greek mythology, Selene was the goddess of the Moon and sister of Helios the Sun god. She fell in love with a shepherd named Endymion and lulled him into an eternal sleep so that he could never leave her.
In terms of astrology, the Sun sign shapes outwardly visible ways whilst the Moon sign effects are more subtle and internal. The Moon rules emotions, dreams and subconscious and it shapes innermost fears, desires loves and needs. When in harmony with the other planets in a horoscope, emotions and desires are in harmony with the reality of life making a person fulfilled and emotionally stable. When afflicted (disharmonious) with other planets in the horoscope the dark side of a person tends to emerge – anger, jealousy, hate, fear and depression.