why do we see the moon during the day
Any clear morning this week around 10 a. m. you can see the moon riding high in the western sky. Many people are surprised to see the moon in full daylight, yet it is a completely normal occurrence. A very common misconception in astronomy is that the moon is directly opposite the sun in the sky. In fact, the moon is only in this position for a single instant in the whole lunar month: the exact time of, when it is 180 degrees away from the sun. The rest of the month it can be anywhere from 0 to180 degrees away and, at least in theory, visible in the daytime sky. At full moon, the moon is exactly opposite the sun. This means that the moon rises just as the sun is setting, and sets just as the sun is rising. This is also the only night in the month when a lunar eclipse can happen. Even so, eclipses normally happen only one full moon out of every six; the other times the Earth's shadow is either too high or too low to touch the moon. Two things contribute to the moon being visible in daylight. First, it is bright enough that its light penetrates the
of the sky. If you're looking at exactly the right spot with a telescope, you can also see the planets Mercury, Venus, and Jupiter in daylight, plus a few of the brightest stars (though few casual observers can actually pull this off).
Secondly, the moon must be high enough in the sky to be visible. Because of the Earth's rotation, the moon is above the horizon roughly 12 hours out of every 24. Since those 12 hours almost never coincide with the roughly 12 hours of daylight in every 24 hours, the possible window for observing the moon in daylight averages about 6 hours a day. The moon is visible in daylight nearly every day, the exceptions being close to new moon, when the moon is too close to the sun to be visible, and close to full moon when it is only visible at night. The best times in the month to see the moon in daylight are close to first and last quarter, when the moon is 90 degrees away from the sun in the sky. That's the situation this week. Last quarter is on Saturday, Sept. 12. If we set to that date, and its location to New York, we see that the moon rises at 11:06 p. m. the night before. The sun rises at 6:34 a. m. , at which time the moon is 74 degrees above the horizon, almost overhead. Sun and moon will both be above the horizon until the moon sets at 3:03 p. m. , although the moon will be hard to see for the last hour or so because of horizon haze. Similarly, the moon will be well placed for daytime observation near first quarter, which next falls on Saturday, Sept. 26.
The difference here is that the sun will be leading the moon, setting at 6:46 p. m. , followed by moonset at 12:06 a. m. Once you've seen the daylight moon on these easy dates, it's worth trying to see how many days in the month you can manage to spot it. This article was provided to SPACE. com by, the leader in space science curriculum solutions. Two reasons first, the moon is bright enough toВ be seen above the blue/white hue of the sky. Second, the duration for which it is above the horizon of Earth coincides with the sun, making it visible during the daytime. Everyone knows that we can t see stars during the day. The most common explanation for this is that the faint glow of stars is washed out by the incredible illumination of the sun in the sky. Folks who are a bit nerdier will go a step further and tell you that the stars are actually washed out because of the Earthвs atmosphere, which scatters the sunlight reaching our planet. Just like stars, we cannot (usually) see the moon during the daytime. However, there are days when you can clearly see the moon during daytime. Why is that? You almost certainly know that theВ moon does not give off its own light, but instead reflects the light of the sun to illuminate the night skies on Earth. It is interesting to note that the moon is actually quite dark, so only about 3% of the sunlight hitting the lunar surface is reflected.
However, that scanty 3% of the reflected light is enough to illuminate our night skies back here on Earth. All of this is to say that whileВ the moon is nowhere nearly as bright as the sun, itвs still much brighter than even the brightest star in our night sky. Therefore, it can shine through the white hue of the daytime sky and be visible, even at high noon! The visibility of the moon from Earth depends entirely on the formerвs position in its orbit. The moon completes a revolution around Earth in a little less than 30 days, andВ it appears as different shapes in the sky over that period. These varied shapes are commonly referred to as the eight phases of the moon. During a given portion of that time period (around the time of the full moon), the moon rises as the sun sets because the moon is opposite from the sun in the sky. Therefore, on every full moon, the sun, moon and Earth line up in such a manner that we can watch the sun setting and the moon rising (on the opposite side of the horizon) at about the same time. However, with the passage of each day, the moon keeps getting nearer to the sun until finally it appears to be very close (around the time of a new moon), rising and setting at almost the same time as the sun.
The upshot of this is that the moon becomes less visible at night and more visible during the daytime. Since the Earth is constantly rotating, the moon appears above the horizon for around 12 hours out of the total 24. On some days, these 12 hours coincide with the sunвs 12 hours above the horizon, and lo and behold! We can see moon during the daytime! At that point,В the moon begins to move away from the sun until it gets back to the full moon phase and the cycleВ starts over. Itвs interesting to note that the moon is visible during the daytime almost every day (except on the days when itвs close to the new moon phase), but one needs to look at the sky very carefully to spot it. Thatвs the reason most casual observers cannot see the moon during the daytime every day. For all you stargazers out there, the moon appears in the daytime sky after the full moon phase until a few days before the new moon (itвs not visible around the new moon phase, as the illuminated side of the moon is facing away from the Earth). If you keep track of the phases of the moon on a daily basisВ (hereвs a useful ), you willВ know the exact days when you can spot that faintly luminous, whitish ball in the daytime sky!
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