Astronomy with Finlarg, Part 1: The Earth - Moon System

This is the first installment of a series which is aimed at those who are curious to learn some astronomy. I don't go into huge technical detail, but try to connect the large numbers and scale of the cosmos with everyday things which people can easily relate to.

I 'borrowed' some footage and images from NASA, Wikipedia, Google and various other sources, for which I'm grateful and hope I haven't infringed any copyrights.

Many of the calculations are my own extrapolations. If anyone spots any errors, I'd be grateful if they could let me know and I'll put them right.

Category:

Education

Tags:

• astronomy
• earth
• moon
• gravity
• orbit
• light pollution
• NASA
• apollo
• astronaut
• barycentre
• sun
• star
• stars
• lunar
• science
• educational

[thereforeithought]

Re: jumping 6X higher on the Moon than on Earth, many science fiction stories about Deimos, the small moon of Mars, feature astronauts jumping to great heights due to miniscule gravity. Good reads.

[finlarg]

@thereforeithought I don't have the figures to hand, but I would imagine that the escape velocity of Deimos is quite low, so it might be possible to end up in a separate orbit of Mars?

[thereforeithought]

@finlarg That's what one of the stories said, I was a kid when I read it, and it was science fiction, so it's not reliable, nice idea, though.

[finlarg]

@thereforeithought I just looked up the escape velocity and it seems to be about 15 mph, which is not very fast. So if an astronaut jumped up at a slower velocity, he or she woul slowly float back down. But if they were able to lauch themselves up faster than this, then they'd escape Deimos' gravity altogether and orbit mars as a separate 'satellite'!

[nahaymath]

Thank you for posting this video, finlarg!

I came here to ask one question: astronomers' best theory for how the moon formed was that object X smashed into young earth E, the ejecta then coalesced to become the new moon. How do scientists know it went that way, rather than object X shot in from outer space and got trapped by E's gravity and became the moon itself?

Thanks for replying!

[finlarg]

@nahaymath You're welcome!

To my knowledge, it is because of the geological dating of the moon. It appears to be the same age as the earth, 4.6 billion years. If it originated from elsewhere, then that would be a heck of a coincidence! The moon also seems to be made of similar material to the outer layers of the earth, not it's iron core, so the idea that something collided in a glancing blow and ripped off some of the outer materials seems plausible.

[thereforeithought]

@finlarg I've actually read that a long time ago.

[nahaymath]

@finlarg Thanks! I should have known that.

[finlarg]

@psandbergnz That's kind of how it works, just substitude the string with gravity. Each lunar 'day' lasts a fortnight, followed by a similarly long night.

Check out this animation to see what the earth would look like from the far side of the moon

watch?v=oUgQ3ylaEK4

Notice that the earth moves a bit, which means we don't see the exact same half of the moon, it 'wobbles' a bit. In the animation a month is condensed into about 30 seconds!

[psandbergnz]

@finlarg, your explanation does sound plausible. The same moon face could always point towards the earth if the moon did not rotate, but only the earth did. An analogy might be attaching a string to a tennis ball, and then whirling the ball around you. The point at which the string attaches to the ball is always facing you as you turn around to keep the ball rotating. The string prevents the ball from spinning on its axis.

This earth-moon system could permit day and night on the moon.