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#11 Lunar years

My twin sister went to live on the moon on our 30th birthday. From then on, she counted a year as 365 sunrises, just as we do on Earth. I am now 60. Which birthday did she last celebrate?

#11 Hole of the moon

I punched a hole 6 millimetres across in a piece of paper and held it at arm’s length to look at the full moon. I was pleased to find that the moon filled the hole perfectly. If the moon is 3500 kilometres across, can you estimate how far away it is?

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#10 Betty’s change

Solution

The smallest amount of change you could have received is 30 cents. With no nickels, Betty would have been obliged to give you a quarter – the largest coin that doesn’t take her over the amount that she owes you – and then five pennies (25c+1c+1c+1c+1c+1c), so six coins in total. She could have reduced the number of coins to three by giving you your change in dimes (10c+10c+10c).

Quick Quiz #11

1 Neil Armstrong was the first man to walk on the moon. Who was the last?

2 On 15 April 1970, Fred Haise, James Lovell and John Swigert set a still-unbroken record of 400,171 kilometres for what?

3 Where does our moon rank in the table of solar system satellites by size, relative to their planets?

4 The Chinese probe Chang’e 4 achieved what first on 3 January 2019?

5 What name is given to the Mars-sized object that, according to the giant impact hypothesis, smashed into early Earth, carving out the moon?

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