On September 3rd, the Moon will appear positioned between the Earth and the Sun, enabling us to see almost exactly half of the Moon’s unlit hemisphere, rendering it nearly invisible.
According to the Hanoi Astronomy Society (HAS), at 8:56 AM on September 3rd, the Moon will transit in front of the Sun at a distance of 2 degrees and 16 minutes, becoming obscured by the blinding light from this star for a few days. During the new moon phase, the Moon is situated between the Earth and the Sun, making it appear nearly invisible in the sky with only half of its hemisphere not illuminated.
The Moon will appear as a mere shadow in the sky when viewed from Earth, with only half of it unlit.
The Moon’s orbital movement around the Earth occurs in a cycle of approximately four weeks, resulting in its phases changing periodically from new moon, first quarter, full moon, last quarter, and back to new moon every 29.5 days. This motion also means that the Moon shifts over 12 degrees eastward in the sky from night to night, causing it to rise and set about an hour later each day.
In the days following the new moon, the Moon will be visible in the sky during the late afternoon as a thin crescent, setting just a few hours after sunset. About a week later, the Moon will remain visible in the night sky until midnight.
New Moon observation schedule in Vietnam.
Why can we observe the Moon during the day? The gas particles in the atmosphere, primarily nitrogen and oxygen, reflect short-wavelength light such as blue and violet light. This scattering of light involves absorbing and re-emitting light in different directions, giving the Earth its blue sky.
For us to see the Moon during the day, it must overcome the scattered sunlight. During the two or three days close to the new moon, we can see the Moon in daylight because it is positioned where sunlight strongly illuminates the Moon.
Due to the Moon’s proximity to Earth, with an average distance of 384,400 km, the light it reflects appears much brighter than distant luminous or light-reflecting objects, such as stars and other planets.
The stars we see shine millions of times weaker than the Sun and millions of times weaker than the Moon. The scattered sunlight is so strong that it often overshadows the stars during the day, though it does not always overshadow the light reflected by the Moon.
Astronomers use surface brightness to measure the apparent brightness of objects in the sky, such as galaxies or nebulae, by measuring the amount of light they emit across a range in the sky when observed from Earth. Since the Moon is closer to Earth than the stars, its surface brightness exceeds that of the sky, making it possible to see it even during the day.
However, whether we can see the Moon during the day depends on several factors, such as the season, the Moon’s phase, and sky clarity.
Another phenomenon that affects our ability to see the Moon is Earthshine. During crescent moon days, when the Moon is nearly aligned with the Sun, you can see the dark side of the Moon that we normally do not see, due to the Moon receiving reflected light from the Earth. The best time to observe this phenomenon is during crescent moon days, approximately 3-4 days after the new moon.
