Phases of an orbit

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After all the theory, let’s move on to a more practical and visible topic, the phases of the moon. The change of its phases from the new moon, which is invisible for us, to the full moon, which dominates the sky, we owe to the fact that the half of the moon facing the sun is always illuminated by it on the one hand, but the part of this half that we can see on the earth on the other hand depends on where the moon is in its orbit.

New moon
The game always begins with the new moon, when La Luna stands exactly between the earth and the sun and this shines on its side facing away from us. The new moon rises and also sets approximately with the sun and is accordingly to be guessed only during the day hours in the sky. The night remains moonless. The rising points move through the seasons as follows: from southeast to north-northeast in spring, from north-northeast to northeast in summer, from northeast to southeast in fall, and from south-southeast to southeast in winter. The setting points shift analogously in the western sky. However, if the moon is exactly between the sun and the earth, it can cover the sun for observers on earth. This is called a solar eclipse. This is only visible from a small part of the earth.

Phase		New moon
Rise		Sunrise
Culmination	Noon
Set		Sunset
Visibility	Invisible, because during the day in the sky	

Waxing crescent moon or first quarter
After the new moon, the waxing crescent moon moves eastward and is therefore visible from mid-morning until after sunset, two to three days after this date. The twilight of dusk is the best time to observe the crescent, which is then a little east of the sun.

Phase		First quarter
Rise		Noon
Culmination	Sunset
Set		Midnight
Visibility	Evening, 1st half of the night

In the phase of the waxing crescent moon (or first quarter), about one week after the new moon, the moon is at 90° to the earth and sun and presents exactly one illuminated half of its day side. During this phase, it rises in the late morning or midday, stands in the south at sunset, and sets during the first half of the night, around midnight. In clear weather, it can be seen already in the afternoon hours because its brightness has already increased considerably and illuminates the evening hours away from artificially illuminated areas. The rising points move through the seasons as follows: from north-northeast to northeast in spring, from east to south-southeast in summer, from south-southeast to southeast in autumn, and from east to south-southeast in winter. The setting points shift analogously in the western sky.

Full moon
The climax of the 29.53-day cycle is the full moon, which our ancestors already considered to have mythical powers. On its orbit, the moon is now exactly opposite the sun, illuminating its entire side facing the earth. Despite its brightness being only one millionth of the sun’s, it provides enough light to comfortably read a newspaper. At this time it appears in the sky at about sunset and remains until it rises again. The rising points move through the seasons as follows: from northeast to southeast in spring, from south-southeast to southeast in summer, from east to northeast in fall, and from north-northeast to northeast in winter. The setting points shift analogously in the western sky.
If the moon is especially close to the connecting line sun-earth, it can be eclipsed by the shadow of the earth and a lunar eclipse occurs. This is visible from all places, where the moon stands in the sky or the sun has set or not risen yet. Because the orbital plane of the moon is inclined to the orbital plane of the earth, a lunar eclipse does not take place every month.
That the full moon appears to us like a flat disk and not like a three-dimensional sphere is due to the reflective properties of its surface. When a sphere receives direct front illumination, its brightness typically decreases from the center outward due to the light striking the edges at a shallower angle. This decrease in brightness gives the object its plastic appearance. However, the rocks of the lunar surface, aluminum and calcium silicates in the mountainous regions and volcanic basalt in the deeply sunken maria, whose brightness drops by 20% due to these structural differences, scatter the incident sunlight evenly in all directions, depriving us of the clue needed to construct spatial depth.

Phase		Full moon
Rise		Sunset
Culmination	Midnight
Set		Sunrise
Visibilty	All night

Waning crescent or last quarter

On the following 180° of the orbit, now everything reverses. Following the full moon, there is a delay in the moonrise, allowing the waning moon to become visible between the late evening and morning. When the moon reaches its last quarter position, it is once again at a right angle to the sun and earth, meaning it is as far away from the sun as the earth, revealing only one illuminated half. At midnight, the moon rises approximately in the east, moves to the south at sunrise, and stays above the horizon until late morning or midday.
The rising points move through the seasons as follows: from south-southeast to southeast in spring, from southeast to northeast in summer, from north-northeast to northeast in fall, and from northeast to southeast in winter. The setting points shift analogously in the western sky.
In the remaining few days until the new moon, almost the whole night remains moonless because the waning crescent moon appears only shortly before sunrise in the eastern sky and remains until noon.

Phase		Last quarter
Rise		Midnight
Culmination	Sunrise
Set		Noon
Visibility	2nd half of night, morning

During the waxing phase at the beginning of the first quarter and the waning phase at the end of the last quarter, when the moon presents itself to us as a narrow crescent, its unlit part appears to us as almost eerily luminous, allowing us to clearly recognize some details of its actually dark surface. The earth’s reflection of sunlight to the moon, resulting from the opposing phases of both celestial bodies, causes this phenomenon known as earthshine. Therefore, when the moon appears to us as a crescent, the earth is nearly full from the moon’s perspective, reflecting so much light that it bathes its surface in almost blinding brightness (the earth’s reflected light is about five times brighter than the moon’s appearance to us in reverse). To capture the earthshine on a photo, the following guideline is valid as orientation: f/5.6 at 8 seconds exposure time with ASA 100 sensitivity and 100 mm focal length (why this last specification is important, we learn a bit further down), respectively f/2.8 and 2 seconds at 300 mm focal length. Again, it doesn’t hurt to bracket from the maximum value given above to the shorter one.

Next Geometry alone does not make a good picture

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