BBC Knowledge April 2017

HIGHEST FLYING BIRDS

Rüppell’s griffon vulture

Altitude: 11,300m

Distribution: Sahel region,

Africa

Lammergeier

Altitude: 7,300m

Distribution: Mountains in

Europe, Asia and Africa

Bar-headed goose

Altitude: 6,437m

Distribution: Central

and South Asia

Andean condor

Altitude: 6,500m

Distribution: Andes,

South America

Mallard

Altitude: 6,400m

Distribution: Europe,

Asia and North America

Bar-tailed godwit

Altitude: 6,000m

Distribution: Northern Europe,

northern Asia and Alaska

White stork

Altitude: 4,800m

Distribution: Europe, North

Africa and western Asia

TOP 10

Why are gases

invisible?

Actually, gases aren’t invisible: many are quite brightly coloured.

For example, nitrogen dioxide is brown-y orange, chlorine has

a yellowish green hue and iodine vapour is a vivid purple.

Other gases in the atmosphere (particularly oxygen, carbon dioxide

and water vapour) also absorb light, but at ultraviolet and infrared

wavelengths that we can’t see. There’s a sweet spot between

the absorption spectra of oxygen and water where not much light

gets absorbed. Lo and behold, that’s exactly the range of light

that we’ve evolved to see! So it’s not that gases are invisible,

as such; it’s just that we can’t see atmospheric gases as they don’t

have a colour in the visible range. ML

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Common crane

Altitude: 10,000m

Distribution: Northern Europe

and Asia

Whooper swan

Altitude: 8,200m

Distribution: Europe and Asia

Alpine chough

Altitude: 8,000m

Distribution: Mountains

from Spain to China

It stays right there! Fart gas mostly comes

from the bacteria and yeasts that live in

the large intestine. If you suppress a fart,

it actually just seeps out more quietly,

or you might be able to hang on until

the next time you are on the toilet.

But sooner or later, that fart is coming out! LV

If you hold

in a FART,

where does it go?

18 April 2017

| & ANSWERS

QUESTIONS

ISTOCK,GETTY IMAGES, SCIENCE PHOTO LIBRARY

12 April 2017