The appearance of a crescent moon during the day when the Sun is visible in the sky is due to the relative positions of the Sun, Earth, and Moon. Here's an explanation of why this phenomenon occurs:
Phases of the Moon: The Moon orbits around the Earth, and as it does so, different portions of its sunlit side become visible to observers on Earth. These different phases of the Moon are caused by the changing positions of the Moon, Earth, and Sun.
Crescent Moon: A crescent moon occurs when the illuminated portion of the Moon that we can see from Earth is less than half but more than zero. During a crescent moon phase, sunlight is still reaching the Moon, but only a small portion of the illuminated side is visible from our perspective.
Line of Sight: Even when the Sun is visible in the sky during the day, it doesn't mean that the Earth blocks the Sun's light from reaching the Moon. The Moon and the Sun can both be above the horizon simultaneously, and their positions in the sky determine the visibility of the Moon's phases.
Angular Separation: The key factor is the angular separation between the Sun, Moon, and Earth. When the Sun is high in the sky, the Moon may appear as a crescent because the angle between the Sun and Moon, as observed from Earth, allows only a portion of the illuminated side to be visible.
Atmosphere and Brightness: Additionally, the brightness of the daytime sky can make it more challenging to observe the fainter details of the Moon. The bright sunlight scattered in the Earth's atmosphere can make it difficult to discern the crescent shape clearly, especially when the Sun is near the Moon in the sky.
So, even when the Sun is up in the sky, it is still possible to see a crescent moon during the day because the Sun's position and the angle of sunlight allow a portion of the Moon's illuminated side to be visible, despite the Sun's direct illumination on the Moon.