Universe Today

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The light from the Moon is actually the reflected light from the Sun!

Every second, the Sun is converting 600 million tons of hydrogen into helium. This reaction lets out a tremendous amount of energy. Most of this energy heads off into space, but some of it falls on the planets and the moons in the Solar System. This is why we can see them at all. Without the Sun, only Jupiter and Saturn would be readily detectable in the infrared spectrum, as they give off more heat than they absorb from the Sun.

Different objects in the Solar System have a different amount of reflectivity. Astronomers call reflected light from the Sun albedo. The values for an object’s albedo can range between 0 (dark) and 1 (bright). The albedo for the Moon is 0.12. In other words, the Moon reflects 12% of the sunlight that falls onto it.

The highest albedo in the Solar System is Saturn’s moon Enceladus, with an albedo of .99. In other words, it reflects 99% of the light that falls upon it. This is because it’s composed of mostly ice. Dark objects like asteroids can have an albedo down to 5%.

When the Moon is full, astronomers measure its apparent magnitude at -12.6. This is bright enough to easily walk around in otherwise total darkness; almost bright enough to read.

When there’s a new moon, however, there’s no light from the Sun falling on the Moon, and yet we can still see the surface of the Moon. Where’s the light coming from? The Earth. Astronomers call this reflected light “Earthshine”, and it helps them calculate how much sunlight is falling on the Earth.

So now you know that the light of the Moon actually comes from the Sun, unless it’s coming from the Earth.

Here’s an article we’ve done on Universe Today about Earthshine, and here’s an article about gardening on the Moon.

Here’s an article from Extreme Science about the Moon, and an article from NASA about Earthshine.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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Except for the Sun, the Moon and Venus are the two brightest objects in the sky. You just can’t miss them.

Astronomers measure relative brightness of objects in the sky with a term called magnitude. The Sun has the highest magnitude of any object in the sky, at -26.73 apparent magnitude. The brightness of the Moon, for comparison, has a magnitude of -12.6. These numbers are done on a logarithmic scale. So the brightness of the Sun is actually 449,000 times brighter than the full moon.

The maximum brightness of Venus is -4.7 magnitude, which is a fraction of the brightness of the Moon (and the Sun!).

So why is the Moon so much brighter than Venus? It’s closer. The distance to the Moon is about 384,000 km, while the closest distance to Venus is about 38 million km. In other words, the Moon is about 100 times closer to Earth than Venus.

Both the Moon and Venus can cast shadows when they’re in the sky. The Moon can be bright enough to almost read by. It’s easy to navigate when the full moon is in the sky. When the Moon isn’t in the sky, but Venus is very bright, you have to look carefully to detect shadows cast by Venus.

One of the most amazing things in astronomy is when Venus and the Moon are both in the sky; especially when they’re very close to one another. Make sure you head outside to see the Moon and Venus with your own eyes.

We have done several articles informing readers about times when both the Moon and Venus are visible in the sky. Here’s an example, and here’s another.

And there are some great articles out there on the Internet. Here’s one from SPACE.com, and another from Astronomy Picture of the Day.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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When the NASA astronauts first landed on the Moon, they left a few items on the surface to commemorate their visit. These items included a plaque, mission badges and an American flag. If you’ve ever seen images or video of the flag on the Moon, you might have a few questions.

Why does the flag stand straight out and not just slump down? Here on Earth, flags are pushed out by the wind. Obviously, there’s no wind on the Moon, so what’s holding the flag up? The answer is pretty easy. There’s a rod, sort of the like a curtain rod running across the top. So the flag on the Moon is being held out by the rod and isn’t blowing in the wind.

What makes the flag flap if there’s no wind? You might have also see a few videos of the flag on the Moon waving back and forth. This happened when the astronauts first planted the flag. There’s no wind to make the flag to flag, but there’s also no wind to stop it from moving back and forth. When the astronauts planted the flag on the Moon, they couldn’t help but give it a sideways push. Without the wind resistance the flag would experience on the Earth, the flag can flap back and forth a few times before finally settling down. That’s why it looks like it’s flapping, even though there’s no wind.

There’s another scene where the flag flaps, as the lunar ascent module is taking off. In this case, the exhaust from the rocket is blasting the flag and causing it to flap back and forth. In the case of Apollo 11, the exhaust blast was so strong that the flag actually fell over. Later missions kept the flag much further away from the ascent rocket.

Can we see the flag on the Moon from Earth with a big telescope, or even Hubble? Even though we have some powerful telescopes, they’re just not powerful enough to spot objects the size of a flag on the surface of the Moon. The flag is only a meter across. In fact, you would need a telescope 200 meters across to spot objects that size from here on Earth. Future space missions will return to the Moon, and they should be able to resolve objects as small as the flags on the Moon.

Does the flag mean that the US claims the Moon? Nope, the Moon can’t be owned by anyone. NASA had the astronauts plant the flag to commemorate the journey made by American astronauts, but to not actually claim the Moon for any single nation.

We’ve done a few articles about this topic. Here’s a review of the Mythbusters episode where they debunk the Moon flag myth.

NASA has answered some more questions about the flag on the Moon. Here’s a link to their article. And here’s another article debunking the conspiracy theory that NASA didn’t even go to the Moon.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

References:
NASA Science: The Great Moon Hoax
NASA Apollo 11 Videos

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The 1st man on the moon was the Apollo 11 Commander Neil Armstrong, who made history on July 20, 1969.

The Apollo 11 mission consisted of Command Module Pilot Michael Collins, Lunar Module Pilot Buzz Aldrin and Commander Neil Armstrong. The mission launched atop a Saturn V rocket on July 16, 1969. After a 4 day journey from the Earth to the Moon, the lunar module detached from the command module and landed on the surface of the Moon in the southern Sea of Tranquility.

The crew remained inside the module for 6 and a half hours, preparing to make their exit onto the lunar surface. And then Neil Armstrong descended the ladder from the lunar module and onto the lunar surface. The first words spoken by the first man on the Moon were, “that’s one small step for (a) man, one giant leap for mankind.”

Buzz Aldrin followed Armstrong, and the two remained on the surface of the Moon for 2.5 hours, taking photographs, collecting rocks, drilling samples, and placing scientific experiments. They they gathered up all their samples, stowed them in the lunar module, and left some souvenirs on the surface of the Moon, like an American flag, Apollo 1 mission patch, and commemorative plaque. They launched again and returned to Earth on July 24.

After the 1st man on the Moon, Neil Armstrong, there were a total of 12 astronauts to walk on the surface of the Moon.

Want to experience what it might have been like to be the first man on the Moon? Here’s a movie review of Fly Me to the Moon.

Of course, NASA has a tremendous amount of information about Apollo 11. Here’s the NASA history page about Apollo 11. And here’s a page that was put together for the 30th anniversary of the first man on the Moon.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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The total surface area of the Moon is 37.9 million square kilometers, or 14.6 million square miles.

Need some context? The surface area of the Earth is 510 million square kilometers. In other words, the total surface area of the Moon is only 7.4% the surface area of the Earth. If you could unwrap the Moon and lay it out flat on the Earth, it wouldn’t fill up Asia, which has an area of 44.4 million square kilometers.

Wondering about some other aspects of the Moon? Here’s an article about the mass of the Moon, and here’s one about the diameter of the Moon.

Want some more general information about the Moon? Check out NASA’s Lunar and Planetary Science page. And here’s the Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?