What is a first crescent? When is the moon truly full? And how can sunlight reflected from Earth illuminate the dark face of the moon? A comprehensive guide to all lunar phases and related phenomena – including Earthlight, Liberation, and the Moon by Day
The rising of the crescent moon, a phenomenon that occurs exactly in the middle of the lunar month (used in the Hebrew and Muslim calendars).
Moon phases: How the appearance of our natural satellite changes throughout the month
The Moon is the closest celestial body to Earth. The average distance from its center to the center of the Earth is about 384,403 kilometers – a distance thirty times greater than the diameter of the Earth. Due to its elliptical orbit, this distance varies between about 363,000 kilometers (at perigee – the closest point in the Moon’s orbit) and about 405,000 kilometers (at apogee – the farthest point). Gravity on the Moon’s surface is significantly weaker: about 1/6 that on Earth.
The Moon orbits the Earth once every 27.3 days – this is the sidereal month (relative to the background of the stars of the Sabbath). But since the Earth itself moves around the Sun, the time it takes for the Moon to return to the same phase (for example, from new moon to new moon) is 29.5 days – this is the synodic month (relative to the Sun). This phenomenon creates the Moon shows – The way we see the illuminated part of the moon changes throughout the month.
The moon does not emit its own light – it reflects the light of the sun. Half of it is always illuminated, but from our perspective the visible part of that illuminated half changes. The result is a cyclical series of eight different lunar phases, which repeat themselves every month.
The eight phases of the moon
- New Moon
Invisible phase: The illuminated side of the moon faces the sun, and the dark side faces the Earth. The moon is more or less in the same direction as the sun, so it rises and sets with it and disappears completely from the sky. It is also usually in the sky during the day – but is hidden by sunlight. - Waxing Crescent
A few days after Christmas, a thin strip of light – a thin crescent – begins to appear in the western sky after sunset. As the days pass, the illuminated area expands, and the moon rises later each evening. - First Quarter
The moon is a third of the way around the Earth, and we see half of its illuminated side – that is, a quarter of the entire moon. People tend to call this phase a “half moon,” but what we see is only half of the illuminated half. It rises at noon, is high in the sky in the evening, and sets around midnight. - Almost Full Moon (Waxing Gibbous)
Most of the moon's surface is already visible in sunlight. Each day presents a larger illuminated area as the moon approaches its full phase. At this stage, it shines in the afternoon and is visible until late at night. - Full Moon
The side of the moon facing the Earth is fully illuminated. This is the state in which the moon is exactly opposite the sun in the sky – so it rises with the sunset and sets with the sunrise. The display appears as a particularly bright and impressive circle, and sometimes occurs simultaneously with phenomena such as a lunar eclipse or supermoon. - Waning Gibbous Moon
Immediately after the full moon, the area of illumination begins to decrease – but most of the moon's surface still appears illuminated. It shines later and longer each night and is mostly visible late at night and early in the morning. - Last Quarter / Third Quarter
Half a moon can be seen again – this time on the other side of the orbit. The moon rises around midnight and is high in the sky in the early morning hours. It sets at noon. - Waning Crescent
The final phase of the cycle. Only a thin strip of light is visible in the early morning, before sunrise. The moon is approaching its next new moon, and the illuminated portion that is visible is shrinking each day.
Other phenomena related to the moon
Liberation – slight fluctuations of the moon
The moon appears stable to us, but in reality it "wobbles" slightly - a phenomenon called LiberationThese movements are caused by three reasons:
- Liberation in length – Due to the moon's elliptical orbit, its speed varies, while its rotation is constant. That's why we sometimes see a little more of the east or west side of its face.
- Liberation in breadth – Caused by the inclination of the orbit relative to the plane of Earth's orbit, so we occasionally see more of the poles.
- Daily Liberation – results from the influence of the observer's position on the Earth and the rotation of the Earth itself.
Earthshine
When the Moon is in a crescent phase, its dark side can sometimes be seen in a faint light – this is sunlight reflected from the Earth onto the Moon’s surface. Since the Earth is almost “full” from the Moon’s perspective, it illuminates its face well – which is what allows us to see details on the Moon’s surface.
Moon in the day
Despite the popular image of the Moon as a nighttime object, it can also be seen in daylight – especially during the first and last quarter phases, when it is at an angle of about 90 degrees from the Sun. In contrast, at a full or new moon – the Moon is not above the horizon during daylight.
Tides, low tides, and the moon's distance from Earth
The moon directly influences the phenomenon The tides and the ebbs on Earth. This effect arises from differences in the intensity of Gravity that the moon exerts on various points on the Earth's surface – a force known as Tidal forceThe differences in gravity create a swelling of the sea surface on the side facing the moon and on the opposite side, and these are expressed in the cycles of tides.
Along with their effect on the oceans, tides also Gradually changing the dynamic relationship between the Earth and the MoonAs a result of the friction created between the ocean water and the seabed, energy is lost from the Earth-Moon system. This energy loss Slows down the Earth's rotation rate Around its axis, meaning the days are getting longer.
in order to maintain Conservation of angular momentum of the entire system, the moon responds by being Gradually moving away from EarthTo measure this distance with great precision, the astronauts of the Apollo 11 mission in 1969 placed Light reflector system On the surface of the moon. This system reflects laser beams sent from Earth, allowing the distance to the moon to be measured with an accuracy of centimeters.
Continuous measurements over decades have shown that The Moon is moving away from Earth at an average rate of about 3.8 cm per year..
To the article on the NASA website
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