Observing the Moon
The Moon is a great starting point for those just getting started stargazing. Not only is it incredibly easy to find, but its close proximity to earth makes its geographic features very visible even with the naked eye. One would suspect that the best time to view to moon would be during a full moon when it’s entire face is lit up. However, the best time to observe the moon’s features are actually when the moon is in between its new and full phases. (The phases are mentioned in more detail below.)
This is true for two main reasons. The first is that the line dividing the light area with the dark area, called the “terminator”, actually creates contrast along this zone, highlighting all the moons features. During a full moon no shadows are cast and all of the craters, valleys, and mountains become somewhat hidden and hard to see. The second reason is that the moon is really bright during a full moon and observing it even with the naked eye, let alone a telescope or binoculars, can be a strain on the eyes and affect your night vision for observing other objects.
Although the light reflected to us by the moon changes over the course of its orbit, the side of the Moon facing us remains constant. The Moon rotates at the same rate that it orbits us ensuring that the same face is always pointing towards us and consequently always keeps the opposite side hidden. This phenomenon is called captured rotation.
The Surface of the Moon
There are many great features to see on the surface of the moon that can be seen from here on Earth. Without any instrumentation at all it is evident that the Moon has very distinct light and dark patches. The dark patches are actually large fields of volcanic rock, formed much earlier in the moon’s history from volcanic activity, and are called maria. Maria is Latin for “seas” which must have been what observers long ago thought the large dark patches resembled.
When viewed through binoculars, the surface features of the Moon become more pronounced and visible. It becomes apparent that the Moon is covered with several thousand craters. Back in the early formation years of the Solar System the Moon was hit with many meteors creating the large craters visible today. The Earth was hit with these meteors as well however over time the craters have been erased through erosion from the wind and the rain, as well as through the movement of the tectonic plates. The Moon however has no atmosphere or an active geology, which leaves the craters preserved for us to observe.
Like the Earth, the Moon has many geological features such as mountains, valleys, flatlands, and canyons. Many of these surface features are best seen through a telescope, as a good telescope will reveal in fine detail an almost endless landscape. Again, these features are usually best seen along the terminator which will cast shadows revealing the shape of the surface in better detail. If you’re interested in observing the details of the Moon’s surface it is recommended you get a good Moon Map, as it will point out the several sights there are to see. Because the Moon is so close and its surface can be seen so well, it is an astronomical target that can be viewed again and again.
Phases of the Moon
The Moon goes through several phases as it circles the Earth. Over its cycle of about 28 days the Moon is orientend differntly in relation to the Sun and Earth and causes the appearance of its illuminated surface to change. The phases are:
New moon: The new moon occurs when the Moon is more less in between the Sun and the Earth. The side that is light up by the Sun’s light is therefore facing away from us. The moon is not visible during this time
Crescent moon: During a crescent moon the Moon is still somewhat in between the Earth and the Sun, yet offset enough to allow us to see it. It appears as a thin sliver of light along the edge of the Moon’s profile.
Quarter moon: A quarter moon is when half of the Moon’s face is bright as seen from the earth. This occurs when the Moon’s position forms a 90 degree angle from the Sun.
Gibbous moon: A gibbous moon is more or less the opposite of a crescent moon, when most of the surface of the moon facing us on Earth is reflecting light from the Sun yet there is a small wedge of darkness.
Full Moon: Finally a full moon is when we are almost directly between the Moon and Sun, which means the whole surface of the moon facing Earth is brightened.
Additionally depending on whether the or not the Moon is becoming more or less full as the days go on the phase is either specified as waxing (increasing) or waning (decreasing). The diagram above shows the Moon’s orientation in relation to the Earth and the Sun along with how it will appear in the sky.
Finding the Moon
The Moon is incredibly easy to spot. It is the second brightest object in the sky behind the Sun, and takes up about the same amount of area in the sky (about half a degree). The only thing semi-challenging about observing the moon is knowing when it will be in sky.
Just like the Sun, the Moon rises and sets as the Earth rotates. The rise and set times are based on what phase the Moon is currently in. The moon is present most of the night during the full moon but is present fewer hours during the night as it approaches the new moon phase when the moon is not visible at all. While the moon is waxing (becoming more full) it is best seen in the early evening as it sets rather early. While the moon is waning (becoming less full) the Moon won’t be visible until it rises late at night. The dates of the phases of the Moon can be found in the Astronomical Calendar.
Facts about the Moon
Distance from the Earth: 385,000 km (239,000 km)
Diameter: 3,474 km (.273 times the Earth)
Mass: 7.348×10^22 kg (0.0123 Earth masses)
Surface Temperature Range: 107°C to -153°C / 225°F to -243°F