Last night, nature put on a fantastic spectacle! For being in the Stockholm area, this was really nice, even the northern lights at zenith. The northern lights, or aurora borealis, are a light phenomenon that occurs when charged particles from the sun collide with gas atoms in the Earth's atmosphere. It is mainly visible in the polar regions (such as northern Sweden, Norway and Iceland) between September and March, often as dancing green, purple or red lights at an altitude of 80–500 km.
Colors: Yellow-green is most common (oxygen at an altitude of 100–140 km). Red and violet tones also occur, depending on the type of atom that collides with the particles.
Shape: They can look like arches, curtains or rays dancing across the sky.
Origin: The northern lights are caused by geomagnetic storms that affect the Earth's magnetic field.
The dark spots you see on the moon are actually giant, solidified lava fields called maria. These were formed billions of years ago when huge amounts of liquid lava gushed out of the moon's interior and filled large craters after meteorite impacts.
Composition: The fields are mainly composed of basalt, a dark, iron-rich volcanic rock similar to that found on the ocean floor here on Earth.
Volcanic activity: It was long thought that volcanism on the moon died out billions of years ago, but new analyses of lunar samples suggest that there may have been active volcanoes as recently as 120 million years ago.
Lava tubes: Beneath the surface are hollow lava tunnels, or lava tubes. These giant caverns are considered ideal locations for future lunar bases because they protect against radiation and extreme temperatures.
Asymmetry: There are significantly more and larger lava fields on the side of the moon that faces Earth than on the far side, which is because the crust is thinner on the front side.
