Post by Centaur on Jul 4, 2009 10:50:15 GMT -6
Big bright Full Moons are especially fascinating for all of us. Amazingly, due to light and shadow effects, a Full Moon is actually twelve times brighter than a Half Moon (first/last quarter position).
It’s not mere imagination that some months a Full Moon appears larger than at other times. And their altitudes at transit can vary considerably over the course of a year and the 18.6-year nodal cycle.
Unfortunately the upcoming Full Moon on 2009 JUL 07 will occur near apogee and appear smaller than average. However, it can just barely be classified as a penumbral lunar eclipse. 16% of the Moon’s diameter will be immersed in the Earth’s penumbra (outer fringe shadow). An astronaut on that portion of the Moon would witness a partial eclipse of the Sun. That event will peak at 09:39 UT (04:39 CDT). At that time the lunar limb will be separated from the Earth’s umbra (dark inner shadow) by 92% of the Moon’s diameter. Any change in brightness should go unnoticed. The following Full Moon on 2009 AUG 05/06 will also present a penumbral eclipse.
I’ve created a diagram with data that demonstrates the variability of the next 15 Full Moons. At the top are the changing declinations which affect the Moon’s altitude at meridian transit. Across the center are seen the relative distances between the Earth and Moon. At the bottom can be seen the changes in the Moon’s apparent angular size due to changes in distance. The graphic can be seen by clicking: www.curtrenz.com/astronomical
It’s not mere imagination that some months a Full Moon appears larger than at other times. And their altitudes at transit can vary considerably over the course of a year and the 18.6-year nodal cycle.
Unfortunately the upcoming Full Moon on 2009 JUL 07 will occur near apogee and appear smaller than average. However, it can just barely be classified as a penumbral lunar eclipse. 16% of the Moon’s diameter will be immersed in the Earth’s penumbra (outer fringe shadow). An astronaut on that portion of the Moon would witness a partial eclipse of the Sun. That event will peak at 09:39 UT (04:39 CDT). At that time the lunar limb will be separated from the Earth’s umbra (dark inner shadow) by 92% of the Moon’s diameter. Any change in brightness should go unnoticed. The following Full Moon on 2009 AUG 05/06 will also present a penumbral eclipse.
I’ve created a diagram with data that demonstrates the variability of the next 15 Full Moons. At the top are the changing declinations which affect the Moon’s altitude at meridian transit. Across the center are seen the relative distances between the Earth and Moon. At the bottom can be seen the changes in the Moon’s apparent angular size due to changes in distance. The graphic can be seen by clicking: www.curtrenz.com/astronomical
