Oversized moon?
Good call; the moon looks larger and often gets a yellow hue during the sultry summer months. Atmospheric differences involving warm air from the gulf of mexico during the summer account for the yellowish color of these summer moons.
Full Moon July 1st weekend looks larger. Is it an illusion? The full Moon, when it first rises during the July 1, 2007 weekend, will be exceptionally low in the sky when compared to other full moons during the year. You will probably think it is larger than normal.
You are viewing the "Moon Illusion".
The Moon is not really larger in size. Your brain only thinks it is larger. The enlarging effect is called the Moon Illusion. The human brain thinks that the sky is shaped like a flattened dome. In other words, the objects on the horizon appear further way than objects higher in the sky.
In the Moon’s case, it is the same distance away from the Earth when it appears near the horizon and when it appears higher in the night sky.
You can find out when the Moon rises during the July 1st weekend by going to the U.S. Naval Observatory webpage. It will ask you to create a USNO listing of moonrises for the entire 2007 year in your local area.
Lunar phases occur because we observe the illuminated half of the Moon from different arrangements of observations due to the interactions of the Earth, Moon, and Sun. That is, we see different phases of the Moon generally because (1) the orbit of the Moon around the Earth is tilted by about five degrees when compared to the Earth’s plane as it moves around the Sun and (2) the Earth is tilted about 23.5 degrees on its own rotational axis.
Thus, the Moon’s movement across the sky can be higher or lower depending on these geometries of movements among the Earth, Moon, and Sun. When the Moon is closer to the horizon, the brain perceives it to be farther away than when it is moving higher in the sky. Maybe it has to do with seeing it near the horizon along with trees, mountains, and other earthbound objects. In any case, the brain miscalculates the true distance that the Moon is positioned away from the Earth when it is closer to the horizon when compared to when it is higher in the sky.
An experiment that you can do a home may help to clarify the Moon Illusion. Draw a set of straight railroad tracks on a piece of paper with a pencil so they appear to be going away from you. Thus, the two tracks are wider at the bottom of the paper and closer together at the top.
Draw lines across the tracks (to represent the wooden ties that the tracks are laid on)—making them shorter as you go up the paper to further show that the railroad tracks are going away from you. You are now looking at railroad tracks going away from you, just like they would appear if you stood on railroad tracks and watched them go off into the distant horizon.
With a colored pen or pencil, draw two equal-in-length horizonal lines (parallel to the wooden ties), one near the bottom of the page (and within the railroad tracks), and another one near the top of the page.
When you look at the two colored lines, does one appear longer than the other? That illusion--you know you drew them equal in length--is just like the Moon Illusion. The Moon appears larger to the brain when you think it is further way—even though it is not further way.
You may also want to do a search of the “Ponzo Illusion”, named after Mario Ponzo, who performed this same experiment in the early 1900s.
So there you have it: watch the Moon the weekend of July 1, 2007 and you’ll see a beautiful full Moon that appears larger near the horizon and appears to slightly shrink in size as it climbs into the night sky.
