Return to Spaceflight


A beginners guide to exploring an alien landscape.

If you have an interest in the heavens as I do, and you live near a large city as I do, you soon discover that it is difficult to see the stars at night. Even under a dark sky, and with a large telescope, the great stellar vistas are still only tiny points of light or dim smudges. Not at all like the photographs. Somewhat disappointing. The Moon however, is big and bright and covered with craters, and even the small drugstore telescope you got for Christmas will reveal tremendous detail from the center of a large city. There is in fact an overwhelming amount of detail visible on the lunar surface, too much to handle in a single night. For that reason I have written this small pamphlet, a short introduction to the Moon. We will cover the Moon one night at a time for one half of a lunar day, following the dawn as it sweeps across the lunar surface to the midday of the full moon. We see much more detail near the sunrise line on the Moon because the shadows of features give a much better measure of their height. The same effect is also visible near the sunset line on the Moon. We will only pick out five to ten prominent features each night, you might pick up few more craters and features in wandering about the surface, and that's OK. On each finder map the numbers refer to the features on Sky Publishing Corporation's excellent and highly recomended lunar map. (item S0003) For this observing program a small two or three inch scope of about fifty power is just fine. Because the Moon is so bright there is no need to wait until your eyes are adapted to the night, and also no need to stumble around in the dark. A nice bright flashlight will not interfere with you observations.

The Moon revolves around the Earth in 27.39 Earth days. It also rotates on it's axis once in the same period, so we see the same face at all times. This gives a lunar inhabitant one very long day, 27.39 Earth days long. On the Moon, the sun rises in the East just like on Earth, and sets in the West just like on Earth. To an inhabitant of the Moon (who for this text will always be on the near side of the Moon) , the Earth has phases just like the Moon, but the Earth rotates rapidly, completing 27.39 revolutions for each phase cycle.

Some facts about the Moon:

Distance from Earth-384,403 km

Inclination of orbit with respect to ecliptic- 5.12 deg.

Diameter-1738 km Earth's diameter-6371 km

Mass-7.3 * 10^22 kg Earth's mass-5.9 * 10^24 kg

Density-3.3 Earth's density-5.5

Synchronous satellite altitude

Moon-86673 km Earth-35676 km

Escape velocity

Moon-2.37 km/sec Earth-11.1 km/sec

Number of people who have walked on the Moon- 12.

Number of people who have walked on the Earth- about 12 Billion!

A note about the maps; Itty bitty moon photos are hard to see, you need big maps which because I print this as a cheap handout will not fit into this limited format, so I have used diagrams based on a sunspot plotting disk, much easier to read. Again, use Sky Publishing Corporation's excellent and highly recomended lunar map for exact locations.

DAY 1, the New Moon.

The new Moon is hidden near the Sun, and very difficult to see. It is the same face that we always see, but the Sun's glare hides it from us. A lunar inhabitant sees a glorious large and very bright full Earth. The lunar surface at new moon is bathed in bright earthshine, but even though it is well light, the Sun is still too bright to see the new Moon from Earth. Despite their great difference in distance, the angular size of the Moon and the Sun are almost exactly the same as seen from the Earth's surface, and the shadow of the Moon sometimes reaches the surface of the Earth. This is a Solar eclipse. Because the Moon's orbit is tilted slightly with respect to the earth sun line, and because the Moon's orbit is slightly eccentric, there is not a solar eclipse at every new moon. For that to happen, everything has to line up just right. In fact as the Moon is being slowly pushed further away from the Earth by the drag of the ocean tides, at some time in the distant future there will be no more total solar eclipses.

DAY 2,

The first crescent of the Moon appears in the West just after sunset. It is somewhat of a contest to see who can spot the earliest crescent Moon, that barely visible sliver of light in the bright sunset sky. In a clear evening sky with a bright Venus as an evening star, the crescent Moon can be a dramatic sight. Because the lunar day is not exactly 28 earth days long, the first crescent appears sometimes earlier, sometimes later. You will have to try your hand at spotting early crescent moons.

For our purposes, we will want a later crescent moon, in a dark sky and one that shows our first set of features. You may have to skip a day to begin observing. Also because the time of the new Moon varies, the features shown on each days finder map may or may not be visible. If not, they will be visible the next day, having moved into the daylight.

Note that the edge of the Moon is rough. This edge is called the limb. As you sweep from the south pole of the Moon to the north pole, you see the brightly light mountains of the Moon against the dark sky. The Moon is in fact very rough. There are hundreds of mountains and millions of craters large and small. Unlike the Earth, the Moon shows nearly every scar from every impact on its face.

On the first evening of observing the Moon we see it low in the western sky just after sunset. First note that while the thin crescent of the Moon is light by the sun, the full orb of the Moon is dimly visible. This is earthshine. As the crescent Moon waxes towards full the glare of the sunlight portion will hide this earthshine.


Starting at the south pole of the Moon which is left, or in an astronomical telescope, to the right:

The crescent really doesn't reach all the way to the pole, so we will first see a group of four craters at about 30 degrees south latitude. Furnerius 111 is a large old crater at the south end of the group. Stevinus 270 may not be visible the first night, but it is located just to the north and east of Furnerius. Senllius 267 is a much deeper crater located just to the south and east of Petavious with a central peak 219 which is the northern most member of this group. Vendelinus 286 lies a bit further north, and Langrenus 166 resides just to the south of the equator all by itself. Mare Crisium is the largest and most visible feature of the early lunar crescent. It is just north of the equator. Cleomedes 68 is a prominent crater on the north shore of Mare Crisium. Geminus 118 is located at 35 degrees north latitude, and is the last prominent crater visible.

As you look at the Moon in a telescope, you will note that the image in the scope will sometimes blur and clear at random. This caused by the heated atmosphere, or seeing. For the first few evenings this will be a problem, but as the observing program moves higher into the sky or later into the night, this seeing problem will lessen.


At about thirty degrees south latitude we again find two craters, Stevinus 270 and Senllius 267 just to the north. these lie between and just to the west of Furnerius 111 and Petavious 219, making a distinctive group. The eastern shore of Mare Fecunditatis is now visible. Cleomedes 68 is a prominent crater on the north shore of Mare Crisium and Burckhardt 49 is visible between it and Geminus 118 which is located at 35 degrees north latitude. Endymion 95 is at 55 degrees north. On a lunar map you will notice that the sunrise line or terminator does in fact lie mostly on a line of longitude. On the Earth, the sun moves north and south of the equator by 23 degrees, so the terminator will only lie on the lines of longitude twice a year at the equinoxes. The Moon's much simpler orbit keeps the terminator close to the longitude lines. This makes life easier for the observer of sunrise sights on the Moon, once the longitude of the terminator is determined from the sighting of a prominent crater, you can sweep along the line to find less prominent features.


On day five the moon stays up a little longer in the evening, and as the surface faces more towards Earth, more detail can be seen. Mare Fecunditatis is the sea of the evening, with Gutenberg 126 on it's southeast shore. Vlacq 290 is prominent at 50 degrees south latitude, with Fabricius 101 a very old crater at about 40 degrees south latitude. Moving north past the western shore of Mare Crisium and then even further north to 48 degrees north latitude we come to Atlas 21. As the sunrise line or terminator moves westward, you can look back to view the craters of the previous day. They will look different with less prominent shadows, but you can now begin to recognize patterns of craters which will help you identify those close to the terminator. Sometimes identifying a crater exactly on the terminator is difficult because you cannot see the pattern of the craters since some are still in the dark.


At about thirty degrees south latitude are three craters that form a short line in the southern highlands. These are, from southeast to northwest, Rabbi Levi 243, Zagut 298, and Wilkins 295. Mare Nectaris is fifteen degrees south of the equator. Ten degrees south of the equator is the prominent crater Theophilus 279. When the light is right you can see its central peak like a white spark above the black shadowed crater floor. Between Mare Tranquillitatis and Mare Serenitatis is the small crater Plinius 232 at eighteen degrees north latitude. Sweeping around the shadowed eastern shore of the Mare Serenitatis we come to the broad shallow crater Posidonius 235 at thirty two degrees north latitude. The small crater Burg 50 in Lacus Mortis at forty five degrees north latitude is the last crater for tonight.


Maurolycus 193 lies in the southern highlands at 40 degrees latitude. The southern highlands are coming into view, so roughness characterizes the lunar surface. At 35 degrees south latitude Gemma Frisius 119 is visible. Geber 117 is at 20 degrees south. Abulfeda 2 is at 12 degrees south. Hunting through the jumble of craters makes finding these three difficult. Get a good map. Manilius 187 sits on the eastern shore of Mare Vaporum. Mare Sernitatis is now fully visible at 25 degrees north with the Causcasus mountains f on the north west shore. Esdoxus 99 and Aristoteles 18 are at 45 and 50 degrees north and very prominent.


1/2 moon or 1st quarter? I say 1/2. The sun crosses the prime meridian of the Moon, and we see 1/2 in light and 1/2 in dark. Tonight's first crater is Walter 291 at 33 degrees south latitude, which has a high central peak to catch the sunlight. Aliacensis 7, Werner 293, and Blanchinus 39 form a line from southeast to northwest. Two wide flat craters at about 12 degrees south are Parrot 216 and Agrippa 5. Triesnecker 283 is 5 degrees north of the equator. At 12 degrees north is Mare Vaporum, and running southwest to northeast are the Apennine Mountains d. At 31 and 35 degrees north latitude are the two prominent craters Autolycus 22 and Aristillus 17 located in the eastern bay of Mare Imbrium. The Alps mountains b lie to the north. A busy night indeed.

Because the terminator is crossing the center of the Moon we see it covering a large angle every day. It seems to move faster across the face of the Moon. This is because the Moon is round, and we cannot see the sides very well. The terminator travels about the same distance on the surface of the Moon every day.


The site of the lunar colony in the movie 2001, Clavius 67 is now in view. Nothing there yet, but you can check at 60 degrees south latitude. One of the newer craters on the Moon is Tycho 284 at about 43 degrees south latitude. The third crater in this row is Gauricus 114 at 33 degrees south latitude. Craters in a row are easier to find. Mare Nubium is now in sunlight at 20 degrees south latitude. Jumping across the equator we come to Eratosthenes 97 at 14 degrees north. Crossing the Mare Imbrium we find Timocharis 28, a newer crater, at 27 N. Our final crater for the evening is in the far north, Plato 230, at 52 N.

DAY 10

The waxing gibbous moon. The jumble of the southern highlands is now fully visible with Blancanus 38 at 65 degrees south. heading north we find Longomontanus 179 at 50 south and then Wilhelm 294 at 45 south. The next prominent crater of the evening is Bullialdus 48 which sits on the south east shore of Mare Nubium at 20 degrees south latitude. Near the equator lie two small craters Lansberg C 161 and Reinhold 248. The great crater Copernicus 74 with it central peak is now fully visible just north of the equator. Farther to the north, the Carpathian mountains e form the southern shore of Mare Imbrium. Sinus Iridum forms a bay on the northwest shores of Mare Imbrium with the Jura Mountains m in strong relief.

The large Mare of the Moon are in fact great impact craters. Beneath the surface lie mass concentrations, MASCONS, the remains of great asteroids, which give the Moon a lumpy gravity field.

DAY 11

Today we will try for a crater very near the South pole of the Moon, Casatus 56 at 75 degrees south latitude. Heading North we find two very unusual craters, Hainzel 128 at latitude forty two south and just to the south and west Schiller 262. These appear as long troughs on the lunar surface, not your usual round craters. Gassendi 113 is a large crater which sits on a point between Mare Humorum and an arm of Oceanus Procellarum. North of the equator and in the middle of the Oceanus Procellarum lies Kepler 155, a newer crater with rays. Heading to the far reaches of the north polar region north of Mare Frigoris, we find Philolaus 220 at 70 degrees north latitude. Craters near the pole are best visible when the lunar libration rocks them toward us.

DAY 12

We are now approaching the western limb of the Moon. In the southern latitudes we see two wide flat craters, Phocylides 221 and Schickard 261. Mersenius 197 lies to the west of Mare Humorum. We then sweep north to a small crater just over the equator, Reiner 247 which sits all by itself in the flat bed of the ocean. Aristarchus 16 and Herodotus 139 are at 25 degrees north. Far to the north is a small group of craters on the flanks of the Jara Mountains m. Among the prominent members of this group are Sharp 265, Bianchini 33, and Harpalus 131.

DAY 13

We are very near the full Moon, and the brightness of the orb might make observing difficult. A neutral filter or sunglasses might help to dim the glare. Zucchius 299 and Bettinus 32 are at 65 degrees south. Cruger 75 is at 18 degrees south. The crater Grimaldi 123 appears like a small sea on the western limb of the Moon just south of the equator. Lunar libration may make these features easy to see or hide them from you. At this late date the limb is almost full light, and the moon appears almost full. Cardanus 55 and Kraft 160 are just north of the equator. Seleucus 264, and Struve 274 form a group at 20 degrees north. We can now fully observe the Sinus Roris as an extension of the Mare Frigoris, the northern most sea.

DAY 14

The ray systems of Tycho 284 (42S, 10W) and Copernicus 74 (10N, 20W) dominate the surface of the full Moon. These are best viewed by the reflected light at high noon on the Moon. It is thought that the ray material sprayed across the lunar surface form these recent impacts is still very fresh, and over many millions of years will slowly darken. Smaller ray systems are associated with the craters Proclus 237 (18N, 48E), Kepler 155 (8N, 38W), and Aristarchus 16 (22N, 48W).

This is also a good time to talk about libration. As the Moon revolves around the Earth, the point on the surface where the Earth is directly overhead moves east and west and north and south. Actually about 6 deg 17 min. in longitude and 6 deg 41 min. in latitude. This gives us an opportunity to see slightly more than half of the lunar surface, 59%. It's never a whole lot more, but until the first good lunar probe photos were sent to Earth in the 1960's, astronomers used lunar librations to try to map every possible inch of the lunar surface. An interesting technique was to project a lunar photo onto a round white ball. This allowed a better view of features on the limb of the Moon.

DAY 15 TO 28

As the sunset crosses the lunar face, you will see many other features on the lunar surface. This will of course involve staying up very late or getting up very early to see the Moon. I will leave this and the rest of the craters on the Moon for you to explore on your own. Of the millions of craters and features on the Moon we have spotted about 92, so there are lots left for you to find!

Return to Spaceflight