"For centuries, people thought the moon was made of green cheese. Then the astronauts found that the moon is really a big hard rock. That's what happens to cheese when you leave it out."
Author Unknown

Astronomy and Cosmology were perhaps the very first attempts that humans made to do science. A few categories of information are below, please browse about and be sure to visit the Question Board if you'd like to ask a question or post a comment!

Solar System Data

Our Moon, Luna

Astronomical Objects

General Relativity

Name	Distance (km)	Radius (km)	Mass (kg)	Gravity (g)	Surface (C)	Atmosphere
Sun	0	697000	1.99e30	27.851	6000	H, He
Mercury	5.791e7	2439	3.30e23	0.378	167	none
Venus	1.082e8	6052	4.87e24	0.907	457	CO2, N2
Earth	1.496e8	6378	5.98e24	1.000	14	N2, O2, Ar
Mars	2.279e8	3398	6.42e23	0.377	-55	CO2, N2, Ar
Jupiter	7.780e8	71492	1.90e27	2.364	-153	H2, He
Saturn	1.429e9	60268	5.69e26	0.916	-185	H2, He
Uranus	2.871e9	25559	8.69e25	0.889	-214	H2, He, CH4
Neptune	4.504e9	24764	1.02e26	1.125	-225	H2, He, CH4
Pluto	5.914e9	1160	1.32e22	0.067	-236	N2, CH4, CO

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So much depends upon the moon... Entire calendars are based on its movements. Its gravitational force gives us high and low tides, and thus tidal pools, a possible starting location for life on this planet!

Formation Theories

How did the moon come to be? Well, there are various theories, but the one that best fits our available data is the Impact Theory. Impact Theory, first suggested in the mid-1970s by William Hartman and Don Davis of the Planetary Science Institute, states that the moon formed following a cataclysmic impact between the young, still mostly molten Earth and a large chunk of stuff (large, like really large, like the size of Mars large). The impact caused the Earth to vibrate violently, thereby sloughing off some of its own material, which became the moon. This is the theory most widely accepted by planetary scientists, but really we need more data to choose it conclusively above the other theory candidates.

I'll give a brief rundown of some of the competing theories. Fission theory says that the rapidly spinning, young Earth simply ejected material in order to stabilize itself. Coaccretion theory says that the moon formed on its own, along with the other planets and moons, out of material in orbit around the Earth. And Capture theory says that moon formed on its own, away from the Earth, then was captured by the Earth's gravitational pull when it ventured too close. Oh, and one more theory: the Birth theory conjectures that the Earth, a whimsical maiden in love with the fiery Sun, had a child by the Sun. That child grew from the Earth (somewhere around the Pacific Ocean), and was born Luna, the Moon. But that's more myth (see below) than scientific theory... :)

Lunar Landings

There were six successful Lunar Landing missions, Apollo 11, 12, 14, 15, 16, and 17. Some details of each mission appear below.

Apollo	Date	Crew	Mission
11	11 Jul, 1969	N. Armstrong, M. Collins, E. Aldrin	Core samples
12	18 Nov, 1969	C. Conrad, R. Gordon, A. Bean	Collected Surveyor 3 parts
14	3 Feb, 1971	A. Shepard, S. Roosa, E. Mitchell	Geological experiments
15	30 Jul, 1971	D. Scott, J. Irwin, A. Worden	Used new Lunar Rover, space walk
16	20 Apr, 1972	J. Young, T. Mattingly, C. Duke	Three days on moon
17	11 Dec, 1972	E. Cernan, R. Evans, H. Schmitt	Last men on moon

Mythology of the Moon

The moon features prominantly in all mythologies! It is, of course, impossible to know each and every way the moon has been used in belief systems and mythology, but here are a few. Also, you may wonder why I present mythology on a science-based site... Well, science is a process of coming to understand something. Mythology is a process of attempting to place meaning and find significance to our existence. No, they are not the same, but there can be no doubt of the power of myth, both as a tool to understand the world, and more importantly as a tool to understand ourselves. We can learn a tremendous amount about a culture simply by understanding its myths. Thus, while mythology itself is not scientific, per se, the study of mythology is crucial to our human understanding. It would be a deep and unforgivable tragedy if we viewed science as a tool to "bust" these mythologies; the myths serve necessary roles in our human psyches, something that science should not, and could not replace.

Siberian Moon Myth
The sun and moon began as earth-based gods, but were captured by the jealous Earth. Porcupine was chosen to rescue the gods from the Earth, and he took advantge of a Siberian custom to do so. Porcupine paid the Earth a visit, thus obligating the Earth to offer a meal and a gift. Porcupine graciously accepted the simple meal, but requested a Mirage Horse and Echo Spear as his gift. These things did not exist, so the Earth was compelled to offer his most prized posessions, the sun and moon gods! Once he had freed the gods, Porcupine threw them into the air, never to be captured again.

Native American Story
The sun and moon were an anti-social, married couple who preferred keeping to themselves in their cabin. The animals, naturally, wanted the sun and moon to come out of their cabin! So, and angleworm drilled small holes in the cabin, through which a gopher stuck a large number of fleas. Bothered incessently by the fleas, the sun and moon fled to the sky.

Greek Diety Artemis
Artemis was the Greek moon Goddess, brother of Apollo. She was also known as the Goddess of the Hunt. She was very protective of the chastity of her followers, and turned one poor lass (who had been raped by Zues disguised as Artemis herself) into a bear. She was also very protective of herself, as Prince Actaeon found out. Actaeon was on a hunt, and came upon Artemis bathing during the full moon (as was her custom). Enthralled by her beauty, Actaeon rudely stared at the goddess, who was so disgusted by his impropriety that she turned him into a stag and set his own hunting dogs upon him. He was torn apart.

Christian Creation Myth
The Book of Genesis, from the Bible, details the Hebrew (now Christian) creation myth. The moon is specifically mentioned in Genesis 1:16, "And God made two great lights; the greater light to rule the day, and the lesser light to rule the night..." The greater light is the sun, the lesser light is the moon. Purposes of the moon's creation are given elsewhere in Genesis, focusing on demarking the seasons and providing light on several nights (presumably for night-time travel? If someone knows, please use the Ask feature on the main pages to let me know).

Lunar & Solar Eclipses

... more to come ...

Moon Phases

A common misconception about the phases of the moon is that they are caused by the Earth's shadow being cast upon the surface of the moon. If this were true, then the largest shadow should be cast when the Earth was between the sun and the moon; however, we actually observe the opposite of this! So, the Earth-shadow idea cannot be correct.

So, what does happen to make the moon appear in different phases? It all hinges upon the angle created among the sun, Earth, and moon. If we put the Earth at the vertex, then the line from sun-to-Earth will be one side, and the line from moon-to-Earth will be the other side. Note, these two lines interect at the Earth, which is the definition of vertex. As the moon orbits the Earth, the angle changes. The moon always has one half of it being lit by the sun, and the other half is unlit (just as the Earth is always half daytime, half nighttime). As the angle changes, the amount of the sunlit part of the moon we see changes. For example, at the New Moon, the angle is 0, and we see none of the sunlit part. Whereas, at the Full Moon, the angle is 180, and we see the entire sunlit part. The other phases are differing degrees between the new and full moon.

As the moon moves from new to full, we call it waxing, and while it moves from full to new, we call it waning. So, the first crescent you see after a New Moon is the Waxing Crescent, and the gibbous moon following the Full Moon is the Waning Gibbous. "Gibbous" is one of those words that's just fun to say, over and over again!

Please note that the drawing is not to scale! The sun is just not that close to the Earth, and moon is about 20 times farther away than depicted.

Depending on the night, and the conditions, you can sometimes see the "dark side" of the moon, meaning, it is dark grey rather than completely black. This is due to Earth-shine, which is reflected light from the Earth striking the moon.

Another interesting moon observation is called the 22-degree halo. This is usually seen on a cold night, when certain forms of ice crystals are present in the upper atmosphere. The crystals refract the moonlight, and it looks as though the moon is at the center of a gigantic halo! When you are alone in the North Maine woods, seeing a 22-degree halo is an awesome sight... It's called a 22-degree halo because the halo is in an arc 22 degrees from the moon. Note that the picture shows sunlight rather than moonlight... 22-degree halos are also possible with the sun, but they are much easier to see with the moon (since the moon is so much less bright than the sun).

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There are so many fascinating objects that live out in space! I have used some NASA/Hubble photos to help illustrate the objects.

NEBULAE

Gigantic collections of dust and gas, nebulae act as nurseries for newly born stars. They hold all of the necessary raw materials for star formation. The picture is of the Eskimo Nebula. ... more to come ...

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I have to begin by saying that General Relativity (GR) is a simple, yet difficult topic. How can it be both? It is simple in its concept, which basically states that all matter affects its surrounding space-time. It is difficult in its mathematics, which require non-Euclidian geometries, tensors, and sundry other mathematical devices. In this discussion, I will stress the conceptual aspects of GR, rather than attempt a complete mathematical description. If you are curious about the math, let me know, and I'll add something more about it.

Fundamental Concepts

Space-Time
Like I said above, one concept of GR is that massive objects (anything with mass) causes a deformation in space-time (space-time is space plus one dimension for time). The usual analogy is to imagine a bowling ball sitting on a rubber sheet. Clearly, the sheet bends in response to the weight of the bowling ball!

So, a two-dimensional sheet curves into three dimensions... This suggests that a 3D space (which is composed of three 2D planes) would curve into six dimensions, plus one for time, resulting in a 7D space-time.

The basic concept to the notion of a curved space-time is that any other object that happens by the proximity of the bowling ball will have its motion influenced by the curvature the bowling ball is generating (just as the bowling ball motion will be influenced by the curvature generated by the other object). Thus, the Earth feels the Sun's gravity because of the deformations the Sun generates in our local space-time.

Invariance
Standing on the surface of the Earth, we all feel the effects of the gravitational field. Doing an experiment by timing the fall of a ball, we might measure the speed of the ball to increase by 9.8 meters per second (32 feet per second) every second it falls. We could then conclude that the acceleration felt by the falling ball (from the Earth's gravitational field) is 9.8 meters per second².

Okay, that's pretty basic physics. But suppose we do the same experiments except now we place ourselves on a spacecraft zooming away from the Earth! And also say that this spacecraft is accelerating 9.8 meters per second every second... See where this is going? As you may have guessed, there would be no measurable difference in our experiments! In effect, unless we can "peek" outside the spacecraft, we would have no way of knowing that we weren't simply sitting on the surface of the Earth!

This situation is summed up by the fancy word: Invariance. It is the concept in GR that tells us that gravitational fields are no different than being accelerated with the same magnitude.

Math Concepts

Einstein Field Equations
In its reduced form, the equation describing GR is deceptively simple:

G_ab = 8πT_ab

But the reality of the situation is that each of those symbols represents a tensor (numbers are 0 rank tensors, vectors are 1st rank tensors, matrices are 2nd rank tensors). In addition, the equation is nonlinear (you get different answers with even the same input, depending on other conditions!) and coupled (the variables do not sort themselves out cleanly into their own equations - there's a lot of crossover).

In addition, each of the tensors has 10 independent components! G_ab is the Einstein tensor, measuring the curvature of the space-time, and T_ab is the stress-energy tensor, measuring the quantity of energy/matter causing the curvature.

Solutions of the Einstein Field Equations are called metrics because the tensors are termed metric tensors.

Implications
What all the math tells us is what I already discussed above, namely, that massive objects alters the space-time around them. Other objects respond to this curvature.

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