Facts about Our Moon
• Our Moon is the only natural moon of our planet Earth. It is also the 4th largest moon in our solar system.
Diameter: 2,160 miles
Distance from Earth: 238,856 miles
Atmosphere: No atmosphere
There are many more facts about the Moon at the end of this page.
Most interesting features in a small telescope: Everyone is enthralled seeing craters at higher magnification around the terminator (the “line” that separates the light side from the dark side—visible in the picture to the right). On “good” nights when the air is steady and using magnifications of 100x to 250x, it really does seems like you are flying over these craters and the detail in and around their rims is amazing!
“Greek myth unknowingly hit upon truth with its story that the goddess of the Moon, Selene, was a descendant of Mother Earth or Gaia.”
Of all the celestial objects, the Sun and the Moon command the most attention. The Sun rules by day, and the Moon by night, waxing and waning through phases that make it visually unique.
The Moon has been an integral part of humanity since the earliest times, gracing our skies with a splendor unmatched by any other celestial body. I have often wondered what people in the past thought of the Moon, ever changing, disappearing and even obliterating. To me, it would have been absolutely haunting and mysterious. So, I am glad I live in a time when mostly rational thought rules and we can appreciate the Moon for what it is, a planetary satellite, inextricably bound to us by gravity, but beautiful to behold.
Where did the Moon come from?
The Moon can be seen during the day!
When my daughter was two, we were driving around and I pointed the Moon out to her, plainly visible as a white crescent against the blue daytime sky. Regularly after that, and to my surprise, she would stretch out her arm and point her finger, and say only as a two-year old can, “Moooon.” Her ability to find the Moon during the day became uncanny. Once, I told her, “No, that’s not the Moon,” but on closer examination, I noticed that she was right.
When you start noticing the Moon during the day, you will see it there often. In fact, about the only time that you cannot see the Moon during the day is around New Moon. From New Moon to Full Moon, the Moon trails the Sun. From Full Moon to New Moon, it precedes the Sun.
The same side always faces us. What’s on the back?
What’s on the other side?
Full Moon Nicknames
In the past, the Moon was given 12 nicknames, one for each month of the year. The nicknames that are occasionally used today include Harvest, Hunter, Moon Before Yule and Moon After Yule (Yule refers to Christmas). The Harvest Moon is the Full Moon closest to the Autumnal Equinox (about September 23). The Hunter’s Moon follows Harvest; next comes Moon Before Yule, then Moon After Yule.
Once in a Blue Moon
Man in the Moon
The Moon: Bane of Deep Sky Objects (DSOs)
OBSERVING THE MOON: Phases & Movement
The Moon appears to cycle through phases because it orbits the Earth. In reality, one-half of the Moon is always bathed in sunlight just like with the Earth. So, the phases represent the portion of the sunlit side of the Moon that we see from Earth.
I have found that some individuals do not understand why the Moon has phases. I believe that this misunderstanding is partially because people get confused quickly with explanations involving geometry, which is the case with the Moon’s phases. So, if you are one of these individuals having difficulty understanding the phases of the Moon, I don’t know if I can explain it here to your satisfaction, but I will try.
First, study the picture below which might help you to visualize the different angles of view that account for the phases.
Secondly, you can partake in a “down-to-earth” example that mimics the phases of the Moon. On sunny days, when you are out and about walking the city streets, take a closer look at any smooth round pole that is bathed in sunlight. One “side” or half of any such pole is always lit by sunlight (its day side) while the other half is always “dark” (its night side). On a smooth pole, there is usually a fairly well-defined vertical line dividing the sunlit side from the dark side. Now, walk slowly around the pole, observing and noting the amount of “light” to “dark” that you see from different sides. This is the same effect that accounts for the phases of the Moon, except the Moon moves around us instead of us walking around it.
OBSERVING THE MOON: Through a Telescope
The prime time to observe the Moon is during its waxing and waning phases. Waxing means “adding on” and waning means “subtracting from.” The terminator, the “line” separating the lighted side from the dark side, is present when the Moon is waxing and waning. Craters appear their best (sharpest) when near the terminator because the contrast from the shadows makes them more pronounced. Magnifications from 40x to 250x are recommended. On a night when the atmosphere is steady and using higher magnifications, it can seem like you are flying right about the craters!
The Moon is disappointing to observe around Full Moon. During this time, the entire surface, along with most features, is “washed out.” However, at this time, the rays of craters are at their most pronounced. The crater Tycho’s rays stretch halfway across the hemisphere.
Want to observe features on the dark or night side of the Moon?
Major Features of the Moon
Terminator. The border or “line” separating the lighted side from the dark side. The terminator is absent during Full Moon. Craters appear at their sharpest near the terminator.
Craters. Huge bowl-like depressions on the Moon. Most of the craters on the Moon were formed from meteoroid or cometary impact that ended about 32 billion years ago.
Terrae & Maria. Terms coined by Galileo meaning “highlands” and “seas.” The lighter-colored terrae have the highest concentration of craters and are older than the maria. The darker maria are smoother areas of the Moon and represent 16% of its surface. They are the result of impacts from large asteroids or comets creating fractures to the once molten interior, releasing dark, iron-rich, basalt lava, which flowed upward and outward to create the great plains. They average 500 to 600 feet thick. There are very few maria on the far side of the Moon.
Rille. A long cliff or split in the maria, up to hundreds of miles or kilometers in length. Rilles can be seen in a telescope. They are the result of cracks, fractures or collapses in the maria. The most famous is the Straight Wall, which is very easy to see in any telescope (see picture on this page.
Rays. Bright streaks that radiate from some craters. They represent lighter, reflective material, ejected during the formation of craters and are most pro-nounced around Full Moon. The crater Tycho has the longest rays, spanning one-quarter of the globe. It is estimated that rayed craters are less than one billion years old because the rays of older craters have been eroded by micrometeorites (see picture on this page).
Regolith. A fine grained “soil” that covers the surface of the Moon. Created from the bombardment of the surface by micrometeorites, the regolith varies in depth from 62 to 26 feet in the maria, and to a possible 49 feet in the highlands. The micrometeorites that bombard Earth burn up in the atmosphere.
Moon beams. Any telescope concentrates lots of light when focused on the Moon, which can easily strain your eye unless you use an eyepiece filter (these screw into threads at the bottom of the barrel) to reduce the intensity. A common practice is to purchase two polarizing filters, A, which are rotated against each other to vary the amount of light passing through, B and C. Note: Some inexpensive eyepieces are not threaded to accept filters.
The far side of the Moon is much less interesting than the side facing Earth.
Top. Rays emanating from the southern crater Tycho, and the low contrast, “washed out” look of a fully illuminated Moon.
The phases of the Moon are nothing more than seeing the dayside of the Moon from different angles as it circles Earth. Imagine yourself in the center and visualize what phase of the Moon you would see. A. New Moon — the Moon is next to the Sun during the daytime so you will not see it at all. B. First Quarter — right-half lit. C. Full Moon. D. Third Quarter — left-half lit.
Tidbits about the Moon
How much does the Moon move eastwardly in an hour?
The Moon rises an average of 50 minutes later each day.
The visual diameter of the Moon changes slightly.
What would the Earth appear like from the Moon?
What’s Out Tonight? is sponsored by Ken Press, publisher of astronomy books and charts.