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Why do joints crack?

Who owns the Moon?

Can fish see in the dark?

PHOTOS: ISTOCK X2

Can moons

have moons?

LIAM FARMER, BIRMINGHAM

There is no reason why a

moon could not have a

moon. But for such a ‘sub-

moon’ to survive for any

length of time, it would

require a stable orbit

around its parent moon.

This generally means that

the sub-moon would have

to be quite small and orbit

quite close to the parent

moon. The bigger the sub-

moon is and the further it is

from the parent moon,

the more likely it will be

influenced by the gravitational

attraction of the parent planet. Tidal

forces can also easily prevent a stable

orbit being possible. So, moons of

moons are possible but probably

extremely rare. AG

WINNER!

Liam Farmer win

Universe2Go perso

planetarium (£79, univ

com). This interactive viewer

uses augmented reality to

reveal facts about the night

sky while you stargaze.

QUESTION OF THE MONTH

Why do we get ‘the meat

sweats’?

RHIANNON WELSBY, COLCHESTER

There isn’t much hard research

specif ically into whet her meat ma kes

you sweat, but one possibility is the

‘t her mic effect’ of protein. We digest

protein less efficiently, and for every

100 calories of meat we eat, 20 to 35

calories are wasted as heat, compared

with 5 to 15 calories for fat or

carbohydrate. The sweating may

be necessary to flush away that

waste heat. LV

Why do people get hangry

(angry when hungry)?

ROB WILKS, LEAMINGTON SPA

Maintaining composure in the face of provocation

takes self-control and there’s a long-running

t heor y in psychology t hat states self-cont rol

depends on blood glucose levels. When you

haven’t eaten you have less glucose, meaning that

your tolerance is likely to run out sooner. In one

study, psychologists gave married participants a

voodoo doll to represent their spouse. Each night

for 21 nights, the researchers measured the

participants’ blood glucose levels, and told them to

stick as ma ny pins in t he doll as t hey wa nted based

on how angry they were feeling. The participants with

the lowest glucose levels stuck in the most pins. CJ

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