January 1, 2016

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The Big and Little of It

Originally published February 23, 2005


Image Credit: Anthony Ayiomamitis

The Big and Little of It

The Moon is far from constant. It varies visibly in size and shape more than any other celestial object. But it is harder to tell – almost impossible visibly? – that the Moon also varies in actual size as seen from Earth. The reason for this variation is simple. The Moon’s orbit is elliptical – sometimes it is near Earth and 14 days later it is nearly 50,000 km further away. In other words the lunar distance and size vary by 14% monthly. I wonder when this was observationally discovered? Anthony has captured nearly the maximum variation in the lunar size difference in these two images of full Moons during 2004. Also note that while there is little difference in longitudinal libration, the libration in latitude has tipped the North Pole into a favorable view in the summer image, and the opposite pole is best in December. This image joins the lunar phase poster as an excellent resource for schools and the public.

Chuck Wood

Technical Details:
TeleVue Pronto + TeleVue Zero-Length Adapter + Canon EOS 300d. Full details.

Related Links:
Anthony’s Astro Gallery
Apogee-Perigee Quarters

Yesterday's LPOD: New Light On A Familiar Domefield

Tomorrow's LPOD: Double Your Pleasure

Author & Editor:
Charles A. Wood



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