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Posts Tagged ‘Dark side’

Ephemeris: 04/17/2026 – The Moon’s Far Side isn’t dark!

April 17, 2026 Comments off

This is Bob Moler with Ephemeris for Friday, April 17th. Today the Sun will be up for 13 hours and 35 minutes, setting at 8:30, and it will rise tomorrow at 6:53. The Moon is new today, and won’t be visible.

When I hear discussions about the Artemis 2 missions, some people who ought to know better still refer to the far side of the moon as the dark side. Officially we have the two faces of the moon: the near side and the far side. I’ll even accept front side and back side. Until 1959 no one had ever seen the far side of the moon so it was dark, in the sense that we could not see it. Not dark because of the lack of light. I’ve been thinking about it. The far side sees more light from the sun, so maybe we should call it the bright side. It certainly has fewer maria or seas, those dark patches that we see on the near side of the Moon. There’s only one on the far side, it’s called the Moscow Sea since the Russian spotted first. Mare Orientale, subject of much study by the Artemis 2 crew, straddles the near side-far side line. It’s closer to the sun when it’s fully illuminated than the near side by about half a million miles, and it doesn’t suffer solar eclipses to darken it like the near side, being already in night, like it always is, at full moon.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

Photograph of the crescent Earth setting behind the limb of the Moon by the Artemis 2 crew.
The far side may seem to be the dark side in this photograph of earthset by the Artemis 2 crew. It is as bright as the brightest parts of the near side. These are the crater filled highlands, so it is the exact same brightness as the highlands on the near side. And indeed in traveling to the Moon, when it was seen half near side and half far side, there was no difference in the brightness of the highlands between the two. So the moon is really dark gray in brightness, on average. It reflects something like 12% of the sunlight it receives, while the earth is more than twice that reflectance. Astronomers call that quantity albedo. So the Moon has an albedo of 12% while the Earth has an albedo of something like 29% on average. So the reason the full moon is so bright at night is due to lack of competition from something that’s actually much whiter. Credit: NASA/ESA/CSA -The Artemis 2 crew.
Categories: Astronomical fact, The Moon Tags: ,

Ephemeris: 01/23/2024- The “dark” side of the Moon is its brightest side

January 23, 2024 Comments off

This is Ephemeris for Tuesday, January 23rd. Today the Sun will be up for 9 hours and 27 minutes, setting at 5:38, and it will rise tomorrow at 8:10. The Moon, 2 days before full, will set at 8 o’clock tomorrow morning.

In a couple of days the far side of the Moon will become the dark side for real. It’ll be night when the near side of the moon becomes fully illuminated, the far side will be a night. The far side of the moon actually gets more sunlight than the near side of the moon because it does not suffer solar eclipses. The lunar solar eclipse occurs when we see a lunar eclipse. The Sun is blocked from shining on the Moon. The totality of a lunar solar eclipse lasts much longer than a few minutes that we get when the Moon totally blocks the Sun, the length of totality for the Moon’s solar eclipse can last several hours. The far side of the moon does not see eclipses, and when fully illuminated at what we call new moon it is a quarter of a million miles closer to the Sun than Earth.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.

Addendum

The near side and the far side of the Moon compared
The near side and the far side of the Moon compared. On the far side the only really dark areas are the Moscow Sea at the 10 o’clock position and the crater Tsiolkovsky at the 8 o’clock position. The large semi dark area at the 5 o’clock position is the Aitken basin which would probably be a lot darker if the impact that created it had occurred on the near side of the Moon. Click or tap on the image to enlarge it. Credit NASA, Clementine spacecraft.
Categories: Ephemeris Program, The Moon Tags: , ,

03/11/2019 – Ephemeris – The Moon: Dark side, far side, which is it?

March 11, 2019 Comments off

Ephemeris for Monday, March 11th. Today the Sun will be up for 11 hours and 40 minutes, setting at 7:43, and it will rise tomorrow at 8:01. The Moon, 3 days before first quarter, will set at 12:54 tomorrow morning.

Tonight the Moon is at its crescent phase, meaning it is slightly closer to the Sun than the Earth is. Most of the Moon we see is in night. Some earth shine may be seen on its night side due to the big nearly full Earth shining on it. I get ticked sometimes when someone who knows better, especially in the media, mentions the dark side of the Moon when they should use the term far side, the part of the Moon that permanently faces away from the Earth. When the Chinese Chang’e 4 spacecraft landed on the far side of the Moon recently many headlines proclaimed that it landed on the dark side of the Moon. The Moon has a night side, as does the Earth, but that changes as the Moon rotates in the sunlight.  And the Moon does rotate.  It happens to be in sync with its revolution about the Earth.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Crescent Moon

The crescent Moon tonight at 9 p.m. EDT, March 11, 2019. Created using Stellarium.

Moon ball

Demonstration of the Moon’s crescent phase with the Styrofoam moon ball we use for Project Astro held up to a light off frame to the right. The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off my hand. Note the roughness of the ball is visible only at the terminator.

The crescent Moon and its relation the Earth

The Earth and Moon if seen as a crescent, near side, far side, sunlit side and earth shine. Credit: me.

Categories: Concepts, Ephemeris Program, Phases, The Moon Tags: , , ,