Harish Jharia

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05 November 2011

Moon Phases: How they Differ From Lunar Eclipse?

        Click on the image to see enlarged view

© Harish Jharia

There is a celestial phenomenon called ‘the phases of moon’, in which the moon successively changes its shape, every day, from ‘full moon’ to ‘new moon’ in a fortnight and from ‘new moon’ to ‘full moon’ in the following fortnight. We are going to discuss phases of moon in this article in a common man’s language, without using scientific and astronomical terminologies. 

What are phases of moon?
As you know that the moon does not have its own glow and it would be visible to us only when sunrays fall on its surface. Sunrays illuminate half of the moon that is visible to us and the other half of it left dark and apparently remains invisible to us. This is so because moon is a spherical body. This half lit and half dark moon moves around our earth at different angles on different days. In these successively changing situations, the illuminated portion of moon looks to us in different shapes on different days.  

Full Moon (पूर्णिमा): 
Moon does not glow on its own and is only visible to us when sunrays fall on its surface. Full moon would be visible to us, in its full glow, when earth positions itself in-between sun and moon in a straight line.

New Moon (अमावस्या):
New-moon could be better caller as ‘no-moon’ because moon is not visible on new moon day. This situation arises when the moon positions itself between sun and earth and the dark half of the moon faces towards the earth in its day time. Resultantly, in day time the new moon remains invisible to us.

Phases of moon (चंद्र कलाएँ): 
Whereas, the new-moon remains invisible and full-moon shines in its full glow, the moon takes 15 days for growing from new-moon to full moon, successively increasing in its size day-by-day. From the very next day after new-moon and full-moon the changing sizes of the illuminated moon starts appearing in early mornings and late evenings.

You may refer the above illustration wherein various positions of moon vis-à-vis earth are shown receiving parallel sunrays from their left side. Apparently, the left halves of earth and moon are illuminated with sunlight (day time) and the right halves of those are left dark (night time). The shapes and views of moon (as visible from earth) in three different situations, that is- New-moon, full-moon and half-moon are also illustrated at the bottom of the sketch.

Please also read "Lunar Eclipse: How It Differs From Moon Fazes" to know the difference between Lunar eclipse and lunar phases.

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