The Lunar Observer – Mares and Craters

On January 20, 2014, the sky cleared again just in time for the bitter cold (-20 degrees Celsius). Determined to observe the night sky, taking what I learned from my last observation into account, I decided to point my telescope at the moon.

After aligning my telescope at the moon, I looked through the eyepiece and saw the glory of the waning gibbous moon. I saw all the mares, and craters, especially the ones that were located at the terminator line, which separates the illuminated side and the dark side. It was beautiful. My mission for the night was to find six of the twelve mares and six of the twelve craters on my list for my Observer’s Certificate. Those features that are on my list are:

Mares Craters
Mare Crisium Crater Petavius
Mare Fecunditatis Crater Cleomedes
Mare Nectaris Crater Posidonius
Mare Tranquillitatis Crater Theophilus
Mare Serenitatis Crater Aristoteles
Mare Vaporum Crater Ptolemaeus
Mare Frigoris Crater Plato
Mare Imbrium Crater Tycho
Mare Nubium Crater Clavius
Sinus Iridium Crater Copernicus
Mare Humorum Crater Gassendi
Oceanus Procellarum Crater Gimaldi

For those who don’t know, mares, which translate to seas, are the dark, flat areas on the Moon. They were formed from ancient volcanic eruptions. The mares are much younger than the surrounding areas because they have fewer craters than their surroundings. This suggests that they have formed relatively recently. Interestingly, the majority of the mares on the moon are on the near side of the moon, visible from Earth. Scientists still debate why that is the case. The Observer’s Certificate requires me to find six mares for the certificate.

In addition, I need to find six Craters. Surrounding the Mare are the highlands, which are the lighter features on the Moon that are riddled with craters. Craters are circular formations of varying depth, size, and albedo on the moon. They were formed as a result of collisions with asteroids. Depending on the size, those asteroids could leave a large crater over many km long in diameter like Crater Ptolemaeus at 153 km, or it can leave a small dent like Crater Grace at 1 km. Craters are best viewed at the terminator line, where the mixture of darkness and light give it a very interesting appearance. The image below is the Lunar surface up close with Mares and Craters visible.

Moon Closeup 2

The top-right of Image shows a Mare. Note the many craters in the image.

Looking at the moon, I saw a lot of flat surfaces, and craters, and white areas. At the beginning, I didn’t know where to start. It felt (actually, it was) like looking at another world. I soon decided to start my search at the terminator line. I saw a mare there, but I couldn’t identify it. I also saw a crater right at the terminator line. Eventually, I saw an intense, white crater in the western portion of the moon. Luckily I found a map to refer to, which led me to discover that it is the Crater Copernicus. That discovery gave me a reference point to search for the other features.

Looking at the map, I conjectured that the mare near the terminator line was Mare Crisium. It was very circular, and it connected to the mare beside it. However, I wasn’t certain. I decided to hold off on checking it off my list. Looking around, I found, to the west of Copernicus, a large mare that covered a large portion of the moon. I found that to be the Oceanus Procellarum. I checked it off my list. Soon enough, I decided to return to the unknown mare at the terminator line. I still couldn’t figure out what mare it is. I looked at the same mare on the map, but both images didn’t add up. I suspected that it wasn’t Mare Crisium after all. However, something caught my eye. It was the crater at the terminator line. After looking at my telescope and at the map again, I confirmed that what I saw was Crater Posidonus. This was significant not only because I checked off another object off my list, but I found the terminator line on the map. From that I realized that Mare Crisium is in the shadowed part of the moon, and that the Mare adjacent to Crater Poseidonus was Mare Serenitatis. It propelled me forward in my mission becauase I was able to know, on the map what to look for and what not to look for. I soon continued on my mission.

Soon enough, I found Mare Imbrium located beside Mare Serenitatis. I also realized that another mare near the terminator line was actually Sinus Medii, which was not on my list. Moving forward, I struggled to find more objects for a while. However, I realized that the orientation of the image of the moon on my telescope was confusing me. It prevented me from finding the right lunar features. Therefore, I decided to look at the image a different way. As a result, I was able to find Mare Frigoris, Mare Vaproum, and Mare Nubium. I was also able to find Mare Cognitum before Mare Nubium, but it was not on my list. In between finding those Mares, I was able to find, Crater Grimaldi at the very edge of the moon; Crater Ptolemaeus, which is close to Mare Nubium and Sinus Medii; Crater Plato, near Mare Frigoris, and Mare Imbrium; and after a lot of searching, I finally found Crater Gassendi.

It took me two hours to find those twelve objects. I even had to change the batteries of my telescope before I found Crater Gassendi. However, it was worth it. After that, I decided to call it a night and bring everything back inside to warm up after a cold night.

It was a productive night, which gave me valuable knowledge of the Moon. I hope to keep doing that in the future when the moon is more illuminated.

Here are the links for the maps that I used. They were very useful in identifying and getting acquainted with the Lunar features:

Before we conclude this post, I have a few announcements:

  1. For those who have any questions about astronomy, I will be setting up a facebook page where you can ask those questions. There are no stupid questions here. If you have a question, I will do my best to answer it.
  2. In addition to my posts, I will regularly post a blog entry talking about a specific topic, such as Formation of Planets, Why the rings of Saturn have gaps, or how stars are born.
  3. In addition to my regular posts, I will post every month an update on astronomical events for the month.

Thank you for following me and I hope you continue to enjoy what you read here.


Coursera Class – Introduction to Astronomy.


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