Note on Phases of the Moon

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When we observe the sky daily for some days, we find that the moon changes its shape every day. It is called phases of the moon.

Phases of the moon occur because of following reasons:
  • The moon is the non-luminous body and reflects the sunlight.
  • The moon is revolving around the earth in its elliptical orbit.

phases of the moon
phases of the moon

When the moon forms an angle of 00 from the plane of earth’s orbit, the whole dark part of the moon faces towards the earth and hence any part of the moon is not seen i.e. a new moon(m1). After 24 hours, when the moon forms an angle 120 with the plane of its orbit, a little bright part of the moon faces towards the earth and a minimum part of the moon is seen bright. It is called waxing crescent (m2). When moon forms an angle of 900, the bright part of the moon is seen in the form of the hemisphere which is called a first quarter (m3). When moon forms an angle of 1680, very little part of the moon remains in the dark which is called waxing gibbous (m4). When moon forms an angle of 1800 from the plane, the moon is seen completely round, which is called the full moon. When moon forms an angle of 192o from the plane very little part is covered by the darkness and it is called waning gibbous (m6). When moon forms an angle of 2700, the moon is seen in the form of hemisphere again, which is called last quarter (m7). When moon forms an angle of 3840, very little part of the moon is seen in the sky and it is called waning crescent (m8). After completing an angle of 3600 by the moon in its orbit again, the new moon occurs.

Some interesting facts about the moon:
  • The moon rises about 50 minutes late daily.
  • The time of sunrise and moonrise is same on the new moon.
  • On the full moon, the moon rises, at the time of the sunset.
  • Moon rises at the mid-day on the first quarter.
  • The moon rises at the midnight in the last quarter.
  • The moon rises about 50 minutes after the sunrise on the waxing crescent.
  • The moon rises about 50 minutes before the sunset on the waxing gibbous.

  • When we observe the sky daily for some days, we find that the moon changes its shape every day. It is called phases of the moon
  • When the moon forms an angle of 00 from the plane of earth’s orbit, the whole dark part of the moon faces towards the earth and hence any part of the moon is not seen i.e. is a new moon(m1).
  • After 24 hours, when the moon forms an angle 120 to the plane of its orbit, a little bright part of the moon faces towards the earth and a minimum part of the moon is seen bright. It is called waxing crescent (m2).
  • When moon forms an angle of 1800 from the plane, the moon is seen completely round, which is called full moon. When moon forms an angle of 3840, very little part of the moon is seen in the sky and it is called waning crescent (m8).
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Very Short Questions

The appearance of the moon at different stages during the revolution are called the phases of the moon.

The moon revolves around the earth in elliptical orbit. Hence, the distance between the earth and moon is not constant throughout the year.

The moon looks dimmer before lunar eclipse because the moon enters into the shadow of penumbra region of the earth. As a result, the brightness of moon decreases and looks dimmer.
When the moon is freed from the eclipse, again the moon has to enter into the shadow of a penumbral region. So, the moon takes sometimes to be brighter again after an eclipse.

In the period between new moon and full moon, the bright part of the moon goes on increasing. This duration is called the bright half (Suklapakshya) of the moon. And the period between full moon and new moon when the brightness of moon goes on decresing is called dark half (Krishnapakshya).

The reasons for not occurring solar and lunar eclipse in each new moon and full moon are as follows:

  1. The orbital plane of the sun, moon and the earth do not coincide each other.
  2. The orbital plane of the earth and moon make an angle 5.150 to each other.

The Solar eclipse will occur in every new moon day and lunar eclipse will occur on every full moon day if the moon and earth have the same orbital plane.

The moon looks dimmer before lunar eclipse because the moon enters into the shadow of a penumbral region of the earth. As a result, the brightness of the moon decreases and looks dimmer.

When the moon is freed from the eclipse, again the moon has to enter into the shadow of a penumbral region. So, the moon takes some time to be brighter again after the eclipse.

The moon revolves around the earth from west direction to east. In this process, first of all the eastern part of the moon enters into the umbral shadow of the earth. As a result, the lunar eclipse starts from the eastern part of the moon.

In the period between the new moon to full moon, the bright part of the moon goes on increasing. This duration is called bright half of the moon. The moon is said to be waxing in this duration.

In the period between the full moon and new moon, the bright half goes on decreasing. The duration of the full moon and the new moon is called the dark half of the moon. The moon is said to be wanning in this duration.

The duration of lunar eclipse is more than that of solar eclipse because of the following reasons:

  1. During the lunar eclipse, the moon and the earth both move in the same direction but during the solar eclipse, they move in opposite direction.
  2. Area of the earth's shadow is more than that of the moon's shadow.

The orbital area of the moon is comparatively smaller than the orbital area of the earth. As a result, the moon becomes collinear with the earth and the sun faster causing the increase in the number of lunar eclipses than the solar eclipse.

Total lunar eclipse is seen from all parts of the earth because it is caused by the umbra of the earth, which has more area. But total solar eclipse is not seen from all the parts of the earth because it is caused by the umbra of the moon, which has a very less area. There is a less possibility of casting the umbra again at the same place where the total solar eclipse occurred once. It needs 360 years to repeat a total solar eclipse at the same place.

Moon rising occurs about 50 minutes later daily because to repeat a moon rising at the same place, the earth has to complete one rotation, which is about 24 hours. In this duration, in the direction of the motion of the earth, the moon forms an angle of 120. To cover the extra distance, the earth needs about 50 minutes more. Thus, the moon rising occurs about 50 minutes later daily.

When the moon is forming an angle of 0 degree from the plane of earth's orbit, the whole dark part of the moon is faced towards the earth and hence, any part of the moon is not seen. It is called the new moon.

When the moon is forming an angle of 1800 from the plane of the earth's orbit, the whole bright part of the moon if faced towards the earth and hence all the parts of the moon are seen. It is called the full moon.

Neptune is the farthest planet from the sun in the solar system. Life is not possible on this planet because:

  1. Water is not found here.
  2. Its temperature is very less.
  3. Oxygen is not present on this planet.

It is never annular because annular lunar eclipse occurs only when the earth forms inverted cones in between it and the moon. Because the earth has a larger size than the moon, it is impossible to form such double opposite cones in between them. So, the lunar eclipse is never annular.

Usually, the partial eclipse is caused by penumbra and total eclipse is caused by the umbra. The area of penumbra is more than the area of the umbra. So, partial eclipse stays longer.

In the solar eclipse, the moon obstructs the sunlight, and it revolves around the earth east ward. In this way, the moon obstructs the western region of the sun at first, during the solar eclipse. Hence, solar eclipse begins from western region.

During the total solar eclipse, the corona of the sun can be studied. The scientist can know many new things about the sun and the solar system by studying it. Hence, total solar eclipse is very important for scientists.

0%
  • When moon forms an angle of 180 degree from the plane, the moon is seen completely round, which is called ______.

    full moon


    waxing gibbous


    new moon


    waxing moon


  • The moon rises about _____ daily.

    10 minutes late
    1 hour early
    50 minutes early
    50 minutes late
  • The time of sunrise and moonrise is same in the ______.

    new moon


    waxing moon


    new moon


    waxing gibbous


  • When moon forms an angle of 168 degree, very little part of the moon remains in the dark which is called ______.

    waxing cresent


    new moon


    bright half moon


    waxing gibbous


  • Moon rises at the mid-day on the ______.

    full moon


    waxing cresent


    new moon


    first quarter


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DISCUSSIONS ABOUT THIS NOTE

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Forum Time Replies Report
lokesh

difference betweendark half and bright half


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Difference between dark half and bright half


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uhhhh


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Adaeze Uzor-Enebeli

Did you mention all the phases


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