Mare Humboldtianum
Type: Lunar sea
Size: 280km
Longitude/latitude: 81.5° E, 46.9° N
Age: 3.9 billion years
Best time to see: Two days after new Moon (13–17 January, favourable); one day after full Moon (25/26 January, unfavourable)
Minimum equipment: 10x binoculars
(Humboldt Sea) is a difficulttoobserve dark lava sea in the zone of libration near the Moon'scent of the Moon's globe all the time. The Moon's orbit is elliptical and tilted by approximately 5° to that of Earth. The elliptical nature of the orbit means the apparent speed of the Moon changes over time, constantly speeding up and slowing down. This allows us to peek slightly further around the eastern and western edges of the Moon. Similarly, the Moon's orbital tilt allows us to see slightly more of the northern or southern regions of the Moon.
