full moon just an illusion?

As the full moon rises this Wednesday evening, June 18, many people will be fooled into thinking it's unusually large.

The moon illusion, as it's known, is a trick in our minds that makes the moon seem bigger when it's near the horizon. The effect is most pronounced at full moon. Many people swear it's real, suggesting that perhaps Earth's atmosphere magnifies the moon.

But it really is all in our minds. The moon is not bigger at the horizon than when overhead.

The illusion will be particularly noticeable at this "solstice moon," coming just two days before summer starts in the Northern Hemisphere. The reason, according to NASA, lies in lunar mechanics: The sun and full moon are like kids on a see-saw; when one is high, the other is low. This week's high solstice sun gives us a low, horizon-hugging moon and a strong, long-lasting version of the illusion.

If it's any consolation, space station astronauts report the same effect.

Here's how it works: Your mind believes things on the horizon are farther away than things overhead, because you are used to seeing clouds just a few miles above, but the clouds on the horizon can indeed be hundreds of miles away. So if we think something (such as the moon) is farther away, and it's not, then it seems larger.



If you remain doubtful, test the idea yourself. Go out at moonrise with a small object, perhaps a pencil eraser. Hold it at arm's length as the moon rises and compare the sizes of the moon and the eraser, then repeat the experiment an hour or two later when the moon is high in the sky. A rolled up tube of paper works well, too.

Moonrise times vary by location. On Wednesday, it will come up at these local times at these locations, according to NASA: New York City, 8:58 p.m.; Miami, 8:35 p.m.; Seattle, 9:51 p.m.

The moon rises about 50 minutes earlier Tuesday night, when the effect will also be noticeable because the moon will be nearly full. Oh, and that raises another fallacy: There's no such thing as a full moon.

Additional moonrise times for your location are available from the U.S. Naval Observatory

Good point and great detail on the moon...

The Moon, of course, has been known since prehistoric times. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once per month, the angle between the Earth, the Moon and the Sun changes; we see this as the cycle of the Moon's phases. The time between successive new moons is 29.5 days (709 hours), slightly different from the Moon's orbital period (measured against the stars) since the Earth moves a significant distance in its orbit around the Sun in that time.
The gravitational forces between the Earth and the Moon cause some interesting effects. The most obvious is the tides. The Moon's gravitational attraction is stronger on the side of the Earth nearest to the Moon and weaker on the opposite side. Since the Earth, and particularly the oceans, is not perfectly rigid it is stretched out along the line toward the Moon. From our perspective on the Earth's surface we see two small bulges, one in the direction of the Moon and one directly opposite. The effect is much stronger in the ocean water than in the solid crust so the water bulges are higher. And because the Earth rotates much faster than the Moon moves in its orbit, the bulges move around the Earth about once a day giving two high tides per day. (This is a greatly simplified model; actual tides, especially near the coasts, are much more complicated.)

But the Earth is not completely fluid, either. The Earth's rotation carries the Earth's bulges slightly ahead of the point directly beneath the Moon. This means that the force between the Earth and the Moon is not exactly along the line between their centers producing a torque on the Earth and an accelerating force on the Moon. This causes a net transfer of rotational energy from the Earth to the Moon, slowing down the Earth's rotation by about 1.5 milliseconds/century and raising the Moon into a higher orbit by about 3.8 centimeters per year. (The opposite effect happens to satellites with unusual orbits such as Phobos and Triton).

The asymmetric nature of this gravitational interaction is also responsible for the fact that the Moon rotates synchronously, i.e. it is locked in phase with its orbit so that the same side is always facing toward the Earth. Just as the Earth's rotation is now being slowed by the Moon's influence so in the distant past the Moon's rotation was slowed by the action of the Earth, but in that case the effect was much stronger. When the Moon's rotation rate was slowed to match its orbital period (such that the bulge always faced toward the Earth) there was no longer an off-center torque on the Moon and a stable situation was achieved. The same thing has happened to most of the other satellites in the solar system. Eventually, the Earth's rotation will be slowed to match the Moon's period, too, as is the case with Pluto and Charon.
Actually, the Moon appears to wobble a bit (due to its slightly non-circular orbit) so that a few degrees of the far side can be seen from time to time, but the majority of the far side (left) was completely unknown until the Soviet spacecraft Luna 3 photographed it in 1959. (Note: there is no "dark side" of the Moon; all parts of the Moon get sunlight half the time (except for a few deep craters near the poles). Some uses of the term "dark side" in the past may have referred to the far side as "dark" in the sense of "unknown" (eg "darkest Africa") but even that meaning is no longer valid today!)

The Moon has no atmosphere. But evidence from Clementine suggested that there may be water ice in some deep craters near the Moon's south pole which are permanently shaded. This has now been reinforced by data from Lunar Prospector. There is apparently ice at the north pole as well. A final determination will probably come from NASA's Lunar Reconnaissance Orbiter, scheduled for 2008.

The Moon's crust averages 68 km thick and varies from essentially 0 under Mare Crisium to 107 km north of the crater Korolev on the lunar far side. Below the crust is a mantle and probably a small core (roughly 340 km radius and 2% of the Moon's mass). Unlike the Earth, however, the Moon's interior is no longer active. Curiously, the Moon's center of mass is offset from its geometric center by about 2 km in the direction toward the Earth. Also, the crust is thinner on the near side.


Sorry just a bit about the moon..

If you want to know about the Illusion click on the link:
http://domino.research.ibm.com/comm/pr.nsf/pages/news.20000103_moon_illusion.html

Hope you enjoy...

Nebulator

that was so much info anyway thanks for sharing

hmm so that how it explaines

Hey i saw that last night at our Astronomy Meeting. WSAAG. (Western Sydney Amateur Astronomy Group) It was talked about our guess speaker Dr Fred Watson, he is an Astronomer at Siding Springs, NTH West of Sydney, about 5hr drive.. Yeah it was amazing to see that. You can see it always stays the same side, we never get to see the other side of the moon, the dark side.. It has a sort of a rocking motion. Cool huh

Awesome that what i like to see, great stuff like this..

Where did you get the Gif file from, or Jpeg, which ever..

Nebulator

nebulator wrote:

Hey i saw that last night at our Astronomy Meeting. WSAAG. (Western Sydney Amateur Astronomy Group) It was talked about our guess speaker Dr Fred Watson, he is an Astronomer at Siding Springs, NTH West of Sydney, about 5hr drive.. Yeah it was amazing to see that. You can see it always stays the same side, we never get to see the other side of the moon, the dark side.. It has a sort of a rocking motion. Cool huh

Awesome that what i like to see, great stuff like this..

Where did you get the Gif file from, or Jpeg, which ever..

Nebulator

you could find those gif at photobucket, just serach the keyword like moon gif, star gif or sort of

Search at photobucket, LUNATION.

Cool thanks guys... Hey i if you gus like also send a message or post on my forum for those guys who like science and the universe.. Would be great just to get a few people talking there aswell as here..nebulator.expressfoum.org..

nebulator.

^
^
nice forum...

Thanks ongkhel... Have ou got one would like to have a look? if you have one..

Thanks again for the compliment..

Nebulator