1/14/2024 0 Comments Gibbous moon![]() ![]() It was an impossible situation - which is typically Gibbous. Before the helicopter could pluck them up, it could send rescuers and horses plunging down steep canyon walls. As I reached my turnoff, the helicopter arrived. Walking the horses down the ridge was judged too risky, so plans for a helicopter rescue had been put into motion. A slow news day perhaps, but it was tense all the same. The breaking story was of two horses stranded in the local foothills. I started my drive home and tuned in the all news station on the radio. It is possible to understand the time at which each phase of the Moon will rise, set, and be at its highest in the sky (on the meridian) without having to memorize those details this is done by thinking about the positions of the Moon, Earth, and Sun relative to one another during different times of the month as well as thinking about what sunset, sunrise, and having something high in the sky physically mean in terms of the Earth's orientation in space.The Moon had just entered its Gibbous phase. The cycle then continues with Waxing Crescent, etc. To recap, the phases of the Moon are: Waxing Crescent, First Quarter, Waxing Gibbous (during these three phases, the amount of the lit half of the Moon seen is increasing each night), followed by the Full Moon, followed by Waning Gibbous, Third Quarter, and Waning Crescent (during these three phases, the amount of the lit half of the Moon seen is decreasing each night), followed by the New Moon. Finally, the Moon returns to the New Moon phase, with the Moon in between the Sun and the Earth in space. ![]() ![]() As the amount of the lit half of the Moon that can be seen decreases further, the Moon enters the Waning Crescent phase. This phase is called Third Quarter (though it is sometimes also called Last Quarter). Next, when the Moon has traveled through three-quarters of its orbit around the Earth, half of the lit half of the Moon can be seen this time the left side of the Moon as seen in the sky is lit. We call this phase Waning Gibbous (waning meaning 'growing smaller'). Darkness begins to appear on the right hand side of the Moon. As the Moon continues in its orbit around the Earth, the lit portion of the Moon begins to disappear. The Sun lights up half of the Earth and half of the Moon, and we can see all of that lit half of the Moon here on Earth during the Full Moon. The entire face of the Moon in the sky is lit because the Moon is behind the Earth relative to the Sun. Then, the entire Moon as seen in the sky is lit up. As the Moon continues to orbit around the Earth, more than half of the view of the Moon that can be seen becomes lit. Half of the lit half of the Moon can be seen from Earth the entire right half of the Moon in the sky is visible. The Moon then continues in its orbit until it has traveled one quarter of the way around the Earth. This phase is called Waxing Crescent (waxing meaning 'growing larger'). As it does so, some of the lit half of the Moon begins to be able to be seen on Earth, appearing on the right hand side. The Moon orbits counterclockwise around the Earth as seen from space looking down on the north pole of the Sun, Earth, and Moon. Sunlight falls on the Moon, but those on Earth cannot see any of that light. To start, when the Moon appears in the New Moon phase, the Moon is in between the Sun and the Earth. The outer circle of images show what the Moon looks like during each phase for an observer on Earth in the Northern hemisphere. The cartoon at the center shows the physical positioning of the Earth and Moon relative to each other (and the Sun) at the time of each Moon phase. In this setup, the Sun is off to the right. The diagram above shows the primary phases of the Moon. This day-of-the-month-dependent viewing of different fractions of the sunlit half of the Moon is what gives us the phases of the Moon. However, at any given time, depending on where the Moon is in its orbital path around the Earth, we here on Earth may see all of the sunlit half, none of the sunlit half, or some portion of it. Half of the Moon is always bathed in sunlight, just as half of the Earth always is (and as half of all objects in the Solar System are). Because of this, the same side of the Moon always faces the Earth. The Moon takes one month to orbit the Earth, and it takes one month to rotate on its axis. Image Analysis with Solar System Objects.Image Analysis II - Animation and Stacking.Image Analysis I - Image Processing and the Ring Nebula.Exploring the Sky II - Star Charts and Stellarium.Hertzsprung-Russell Diagram and Star Clusters.ASTR:1771 - Intro Astronomy I: Basic Astrophysics.ASTR:1080 - Exploration of the Solar System.ASTR:1070 - Stars, Galaxies, and the Universe. ![]()
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