What are those blue regions on the Moon?

When gazing at the Moon, you might notice vast, dark plains that early astronomers mistook for seas. These features, known as lunar maria (singular: mare), are not bodies of water but expansive basaltic plains formed by ancient volcanic activity.

The Volcanic Origins of Lunar Maria

Approximately 3 to 4 billion years ago, the Moon experienced significant volcanic activity. Molten basaltic lava flowed across its surface, filling large impact basins and solidifying into the dark plains we observe today. These basaltic regions are less reflective than the surrounding highlands, giving the maria their distinctive dark appearance.

Why Are They Called 'Seas' and how to observe them?

The term maria comes from the Latin word for 'seas.' Early astronomers, observing the Moon through telescopes, believed these dark areas were actual seas. This nomenclature has persisted, even after we understood their true nature.

You can see those sees with your naked eye! I put my favorite ones in this photo above, and those are:

1. Mare Tranquillitatis (Sea of Tranquility). The 876 Km in diameter sea is the landing site of Apollo 11!
2. Mare Serenitatis (Sea of Serenity). The 674 Km sea is located above the Sea of Tranquility and to the East of the Sea of Showers. 
3. Mare Crisium (Sea of Crisis). This 556 Km sea is located to the north east of the Sea of Tranquility, the reason behind the naming is not clear, it was named by an Italian astronomer Giovanni Riccioli and it has since been used as a standard name. 
4. Mare Imbrium (Sea of Showers/Rain). This 1146 Km in diameter sea is actually one of the largest craters in our solar system. It's the second largest mare on the Moon after the Oceanus Procellarum. 
5. Mare Fecunditatis (Sea of Fertility). This 840 Km sea is located to the South east to the Sea of Tranquility. 
6. Mare Cognitum (Sea that has become Unknown). This 350 km in diameter sea is located southern to Oceanus Procellarum and Copernicus Crater. 
7. Mare Humorum (Sea of Moisture). A 420 Km sea that is located to the south of Mare Cognitum, to the west of Tycho Crater. 
8. Oceanus Procellarum (Ocean of Storms). This 2592 Km sea is the largest of the mare and hence called "the Ocean".

Using a telescope or high-resolution lunar maps can enhance your observation experience.

What are the orange and blue colors on my Moon photos? 

Many have wondered and asked me about the blue/rusty colors of the Moon in my photos. 

The blue areas you see are the lunar Mare, and are generally ancient lava flows with high iron and titanium content. The redder/rusty areas have high magnesium content.

While these colors aren't immediately evident to our eye, the camera sensor + saturation boosts can reveal them with great clarity. It's an excellent way to look at some of the formation boundaries on the surface.

Chemical composition

The term of mare constituents is called lunar basalts. Mare basalts are generally grouped into three series based on their major element chemistry: high-Ti basalts, low-Ti basalts, and very-low-Ti (VLT) basalts. While these groups were once thought to be distinct based on the Apollo samples, global remote sensing data from lunar missions now shows that there is a continuum of titanium concentrations between these end members, and that the high-titanium concentrations are the least abundant. Titanium oxide abundances can reach up to 15 wt.% for mare basalts, whereas most terrestrial basalts have abundances much less than 4 wt.%. A special group of lunar basalts is the KREEP basalts, which are abnormally rich in potassium (K), rare-earth elements (REE), and phosphorus (P). A major difference between terrestrial and lunar basalts is the near-total absence of water in any form in the lunar basalts. Lunar basalts do not contain hydrogen-bearing minerals like the amphiboles and phyllosilicates that are common in terrestrial basalts.

Reference

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Interested in bringing the Moon's beauty into your space? Explore our collection of high-resolution lunar prints that showcase the intricate details of lunar maria and other celestial features.