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Moon, Super-Moon, Planets of the Solar System and Star Vega: Brightness and Size

Author(s): Agrawal DC

The Moon, moonlight and phases of the Moon and its relatively simple recurring cycle have been of interest since time immemorial to human beings, navigators, astronomers and astrologers. The fact that the Moon’s orbit is close to the plane of the ecliptic and not to Earth's equatorial plane leads to new Moon to full Moon and solar and lunar eclipses also. During the phase of the full Moon, the luminous flux and its apparent size will depend on its distance from the Earth; when the full Moon is at farthest point called lunar apogee, it will be smallest full moon or micro full moon and whilst it is closest to us termed as lunar perigee will appear macro full moon-better known as super-moon, a term coined by astrologer Richard Nolle in 1979. The expressions for the lunar luminous fluxes on the Earth for the extreme positions lunar apogee and lunar perigee are derived for the first time from the students’ point of view. Furthermore, estimates for apparent magnitudes and apparent sizes of full moons corresponding to these positions are also examined. It is shown that full perigee Moon is about 29% brighter and 14% bigger than the full apogee Moon consistent with numbers available in literature. This paper will motivate the students to apply the techniques learnt here to the case of planets which are revolving around the Sun in their respective elliptical orbits having equivalent extreme positions aphelion and perihelion. In addition, students can also assess apparent magnitude of the reference star Vega.

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