0:00:05 > 0:00:07The sun.
0:00:15 > 0:00:18It creates the daily rhythm for life on Earth.
0:00:26 > 0:00:30A player in almost every drama that unfolds across our planet.
0:00:35 > 0:00:36Hour by hour,
0:00:36 > 0:00:39its exact position is critical.
0:00:55 > 0:00:58For some, it brings moments of enormous opportunity.
0:00:59 > 0:01:02For others, it can spell disaster.
0:01:06 > 0:01:09All over the world, animals' lives are governed
0:01:09 > 0:01:13by the sun's journey through the sky.
0:01:16 > 0:01:20How they respond can make the difference between success
0:01:20 > 0:01:22and failure,
0:01:22 > 0:01:24life or death.
0:01:25 > 0:01:29This is just an ordinary day
0:01:29 > 0:01:31on our extraordinary planet.
0:01:46 > 0:01:47It's dawn.
0:02:00 > 0:02:03The sun hasn't arrived yet,
0:02:03 > 0:02:06but its power will soon be felt,
0:02:06 > 0:02:08and the world is waking.
0:02:10 > 0:02:13HOOTING
0:02:16 > 0:02:19The day starts with a love song.
0:02:19 > 0:02:22HOOTING
0:02:27 > 0:02:30HOOTING
0:02:39 > 0:02:41Lar gibbons.
0:02:46 > 0:02:51With each note, they renew their bond after the long night,
0:02:51 > 0:02:56and remind other gibbons that this patch of forest is theirs.
0:03:01 > 0:03:05They've discovered that the hour before sunrise is the perfect time
0:03:05 > 0:03:06for their duet...
0:03:15 > 0:03:16HOOTING
0:03:16 > 0:03:20..because sound travels furthest in cool air.
0:03:24 > 0:03:28And at dawn, a warm layer sits above the cool air,
0:03:28 > 0:03:31reflecting and amplifying every note.
0:03:35 > 0:03:37It's the best time of the day to be heard,
0:03:37 > 0:03:41and the gibbons aren't the only ones making the most of it.
0:03:41 > 0:03:45BIRD SQUAWKS
0:03:48 > 0:03:52BIRDS CALL
0:04:00 > 0:04:04All over the planet, nature's dawn chorus heralds the moment
0:04:04 > 0:04:06the world's been waiting for.
0:04:24 > 0:04:27SCREECHING
0:04:41 > 0:04:43PENGUINS TRUMPET
0:04:53 > 0:04:56Our star,
0:04:56 > 0:04:58a burning giant,
0:04:58 > 0:05:00reappears above the horizon.
0:05:07 > 0:05:12Its rays, travelling at over 180,000 miles per second...
0:05:14 > 0:05:16..flick the switch
0:05:16 > 0:05:19and the world is flooded with light.
0:05:46 > 0:05:51This meerkat family is up early to greet the sunrise.
0:05:51 > 0:05:54THEY CHIRRUP
0:05:54 > 0:05:57It's not high enough to warm them up just yet...
0:05:59 > 0:06:02..and they're finding it difficult to get going.
0:06:10 > 0:06:12But unbeknown to them, the early light
0:06:12 > 0:06:16is having an extraordinary effect inside their bodies.
0:06:29 > 0:06:32Sunlight triggers the brain to shut off drowsy hormones,
0:06:32 > 0:06:36replacing them with waves of energising ones,
0:06:36 > 0:06:38kick-starting their metabolism
0:06:38 > 0:06:40and preparing them for the day ahead.
0:06:45 > 0:06:48Suddenly, they're wide awake.
0:06:50 > 0:06:52Time to find breakfast.
0:06:59 > 0:07:03All over the world, the rising sun is making its presence felt,
0:07:03 > 0:07:05forcing animals into action.
0:07:13 > 0:07:16For the last eight months, South Africa's rocky shoreline
0:07:16 > 0:07:20has been a nursery for this young Cape fur seal.
0:07:26 > 0:07:29He, too, is hungry, but the need to fuel his body
0:07:29 > 0:07:31is about to get him into trouble.
0:07:39 > 0:07:42Each morning, with the rising sun,
0:07:42 > 0:07:45the current moving past the mouth of the bay brings rich pickings.
0:07:54 > 0:07:57But with opportunity comes danger.
0:08:07 > 0:08:09A killer patrols these waters...
0:08:13 > 0:08:16..waiting for inexperienced pups to take the plunge.
0:08:19 > 0:08:22The older seals know the great whites are out there,
0:08:22 > 0:08:26but by midday, the biggest fish shoals will be out of range.
0:08:27 > 0:08:31The seals must leave now.
0:08:40 > 0:08:43The pups' best chance is to fall in with a convoy of adults.
0:08:46 > 0:08:48Experienced seals are notoriously hard to catch.
0:08:52 > 0:08:55But in the first two hours of the day,
0:08:55 > 0:08:59the great white has a better chance, thanks to an ally.
0:09:01 > 0:09:03The sun itself.
0:09:05 > 0:09:07The early-morning light is strong enough
0:09:07 > 0:09:09to silhouette the pup from below.
0:09:15 > 0:09:18But the slanting rays can't penetrate the depths.
0:09:21 > 0:09:23The shark can see the pup,
0:09:23 > 0:09:25but the pup can't see the shark.
0:10:05 > 0:10:07This time, the pup is just small
0:10:07 > 0:10:10and speedy enough to slip through the shark's jaws.
0:10:15 > 0:10:17Away from the coastline, he's safe.
0:10:24 > 0:10:26And as the sun rises higher,
0:10:26 > 0:10:29illuminating the shadowy depths,
0:10:29 > 0:10:32the shark's window of opportunity closes.
0:10:37 > 0:10:39At least, until tomorrow.
0:10:44 > 0:10:48As the sun climbs higher in the sky,
0:10:48 > 0:10:50its character is changing.
0:10:52 > 0:10:56For the first time in the day, it's not just sensed as light,
0:10:56 > 0:10:58but as radiant heat.
0:10:59 > 0:11:03BIRDS CHIRP
0:11:12 > 0:11:16Clusters of Monarch butterflies huddle close together
0:11:16 > 0:11:18against the chilly Mexican night.
0:11:23 > 0:11:27Up until now, the morning has been too cold to leave the branches.
0:11:30 > 0:11:32But as the sun hits their wings,
0:11:32 > 0:11:36warming their bodies to a crucial 12 degrees, they can finally fly.
0:11:48 > 0:11:51Each cluster revealing tens of thousands
0:11:51 > 0:11:53of individual butterflies.
0:12:03 > 0:12:08The first warmth of the day is just as important to small mammals.
0:12:13 > 0:12:17These Madagascan lemurs aren't meditating.
0:12:17 > 0:12:19They're sunbathing.
0:12:26 > 0:12:29Too small to regulate their body temperature well...
0:12:31 > 0:12:34..they lie back and soak up the warmth
0:12:34 > 0:12:36through their thinly coated underbellies.
0:12:37 > 0:12:40A much-needed morning heat fix.
0:12:45 > 0:12:49But nowhere is the warming of the landscape felt more keenly
0:12:49 > 0:12:51than in the desert...
0:12:52 > 0:12:53..of Namibia.
0:13:02 > 0:13:05Overnight, the temperature hit freezing point.
0:13:05 > 0:13:07But this morning, the sun
0:13:07 > 0:13:10is radiating heat directly onto the sand dunes.
0:13:12 > 0:13:14Three hours after sunrise
0:13:14 > 0:13:18and, already, the temperature has climbed by 30 degrees.
0:13:20 > 0:13:23Exactly what this desert inhabitant has been waiting for.
0:13:32 > 0:13:35The Namaqua is unusual...
0:13:35 > 0:13:38which, for a chameleon, is really saying something.
0:13:42 > 0:13:45Somewhere in its evolution, it drew the short straw.
0:13:53 > 0:13:57So whilst its cousins around the world live hidden in trees,
0:13:57 > 0:14:00the Namaqua is exposed on sand-blasted dunes.
0:14:03 > 0:14:06Just surviving the freezing night
0:14:06 > 0:14:09has left the cold-blooded chameleon sluggish.
0:14:12 > 0:14:15Its energy supplies so drained
0:14:15 > 0:14:17that breakfast passes right under its nose.
0:14:20 > 0:14:23It's going to need to get warm before it can eat.
0:14:43 > 0:14:47By angling its dark brown, scaly skin towards the light,
0:14:47 > 0:14:50it becomes a reptilian solar panel.
0:14:58 > 0:15:02An hour or two on charge and it will be good to go.
0:15:11 > 0:15:14In less extreme parts of Africa,
0:15:14 > 0:15:18this change in air temperature has burnt the hanging morning haze away.
0:15:20 > 0:15:24In just a couple of hours, the ground will become so hot
0:15:24 > 0:15:27that it will begin to generate a heat haze of its own.
0:15:29 > 0:15:32But right now, in this brief window of clarity,
0:15:32 > 0:15:35with nothing to spoil her view,
0:15:35 > 0:15:37conditions for this cheetah
0:15:37 > 0:15:38are perfect.
0:15:43 > 0:15:46She's a mother, with responsibilities.
0:15:46 > 0:15:47Three of them.
0:15:50 > 0:15:52They're growing fast
0:15:52 > 0:15:54and they're hungry.
0:15:56 > 0:15:58Mum needs to make a kill.
0:16:13 > 0:16:16The lions who share her territory
0:16:16 > 0:16:18have excellent night vision.
0:16:19 > 0:16:22But the cheetah's eye is designed for sunlight.
0:16:23 > 0:16:25Packed full of colour receptors,
0:16:25 > 0:16:28she sees the world in razor-sharp detail.
0:16:30 > 0:16:33The lions could threaten her cubs,
0:16:33 > 0:16:35but they're stuffed full from the night's hunt.
0:16:39 > 0:16:42Right now is her best chance.
0:16:52 > 0:16:55Black tear stains under her eyes
0:16:55 > 0:16:57combat glare and help her focus
0:16:57 > 0:16:59in the crisp morning air.
0:17:44 > 0:17:45Just in time.
0:17:46 > 0:17:49The heat haze will soon be shimmering above the ground...
0:17:51 > 0:17:54..making it difficult to see in any detail.
0:17:56 > 0:17:58Then the time for hunting will be over.
0:18:00 > 0:18:01The best option?
0:18:01 > 0:18:03To spend the rest of the day
0:18:03 > 0:18:04in the shade.
0:18:16 > 0:18:18In more temperate parts of the world,
0:18:18 > 0:18:21plants have been working hard since dawn...
0:18:26 > 0:18:29..photosynthesising light into energy.
0:18:32 > 0:18:36In the next hour, the sun's intensity will peak.
0:18:42 > 0:18:45These light harvesters are gearing up for what should be
0:18:45 > 0:18:47the most productive moment of the day...
0:18:49 > 0:18:52..but it's also when the sun becomes its most dangerous.
0:18:58 > 0:19:01As damaging to plant cells as it is to our skin.
0:19:03 > 0:19:07As the sun blasts down from overhead...
0:19:12 > 0:19:14..these sunflowers are carefully monitoring
0:19:14 > 0:19:16its intensity,
0:19:16 > 0:19:20flooding each leaf with a sunscreen,
0:19:20 > 0:19:23protecting the plant from sun damage.
0:19:26 > 0:19:29At 90 degrees, directly overhead...
0:19:30 > 0:19:33..the sun's rays pass through the least atmosphere.
0:20:00 > 0:20:04Millions of watts of energy beat down onto the Earth.
0:20:22 > 0:20:25In the Australian outback,
0:20:25 > 0:20:28temperatures have soared past 50 degrees.
0:20:31 > 0:20:33Out in the open, these kangaroos
0:20:33 > 0:20:35are becoming dangerously hot.
0:20:43 > 0:20:45The shade gives some relief,
0:20:45 > 0:20:47but it's not enough.
0:20:47 > 0:20:49The air surrounding them is baking.
0:20:56 > 0:20:58To prevent heatstroke,
0:20:58 > 0:21:01these roos have a trick or two up their sleeves.
0:21:05 > 0:21:10Along their forearms, vessels full of hot blood run close to the skin.
0:21:15 > 0:21:17They lick themselves.
0:21:27 > 0:21:32As their saliva evaporates, a little body heat is lost with it.
0:21:35 > 0:21:37And by digging away the hottest layers of earth...
0:21:39 > 0:21:42..and resting on the cooler layers below...
0:21:47 > 0:21:52..these resourceful roos have found a way to survive the midday onslaught.
0:22:03 > 0:22:07Shade is hard to come by in the Namibian sand dunes.
0:22:15 > 0:22:16Our cold-blooded chameleon
0:22:16 > 0:22:20is in danger of being cooked in his own skin.
0:22:36 > 0:22:39But life in this uncompromising place
0:22:39 > 0:22:41has forced an incredible adaptation.
0:22:53 > 0:22:56Doing what chameleons all over the world do best,
0:22:56 > 0:22:59it's changed colour.
0:22:59 > 0:23:02Dark brown to brilliant white.
0:23:07 > 0:23:09Reflecting the heat off its skin
0:23:09 > 0:23:11and keeping its internal temperature
0:23:11 > 0:23:13just cool enough to survive...
0:23:17 > 0:23:19..and to hunt.
0:23:28 > 0:23:31A solar-powered, turbo-charged chameleon.
0:23:38 > 0:23:40Well, relatively speaking.
0:23:54 > 0:23:59Not everyone finds the midday sun such a challenge.
0:24:03 > 0:24:06In a lake, on a remote island in the Pacific...
0:24:08 > 0:24:11..a golden jellyfish is sunbathing.
0:24:21 > 0:24:23This is no ordinary jelly.
0:24:27 > 0:24:29Over 12,000 years ago,
0:24:29 > 0:24:31its ancestors were marooned here.
0:24:36 > 0:24:38Faced with starvation,
0:24:38 > 0:24:40this seafarer became a farmer.
0:24:43 > 0:24:46Absorbing lake algae into its body
0:24:46 > 0:24:47and cultivating them.
0:24:51 > 0:24:54The algae use light to photosynthesise,
0:24:54 > 0:24:57sharing the energy generated with their hosts.
0:25:01 > 0:25:03The jellies carefully tend the algae,
0:25:03 > 0:25:05following the path of the sun
0:25:05 > 0:25:07across the lake.
0:25:10 > 0:25:12It's such a successful relationship
0:25:12 > 0:25:16that now, there are 13 million jellies...
0:25:26 > 0:25:30..all clustered under the midday sun.
0:25:32 > 0:25:35Gently spinning, to give their crop
0:25:35 > 0:25:36just the right amount of light.
0:25:48 > 0:25:49From midday onwards,
0:25:49 > 0:25:52the angle of the sun begins to wane.
0:25:54 > 0:25:56But it becomes no less dangerous.
0:26:00 > 0:26:02The ground temperature carries on rising.
0:26:09 > 0:26:12While most animals wait for the Earth to cool...
0:26:15 > 0:26:19..amongst the craggy peaks of the Ethiopian mountains...
0:26:21 > 0:26:23..a quirky-looking crowd is gathering.
0:26:25 > 0:26:29Lammergeyers are vultures, scavengers.
0:26:32 > 0:26:34Collectors of bones.
0:26:36 > 0:26:38Partial to the marrow found inside them.
0:26:41 > 0:26:45Heavy duty stomach acid dissolves small bones,
0:26:45 > 0:26:47but they're not exactly nutritious.
0:26:52 > 0:26:55A lamb femur full of marrow is much more like it.
0:26:58 > 0:26:59But there's a problem -
0:26:59 > 0:27:01the bone's far too big to swallow.
0:27:06 > 0:27:08In the warmth of the afternoon,
0:27:08 > 0:27:11this lammergeyer senses an opportunity.
0:27:16 > 0:27:19Heat, radiating from the plains below,
0:27:19 > 0:27:21has built into huge columns
0:27:21 > 0:27:23rising into the atmosphere.
0:27:28 > 0:27:31Warm-air thermals - perfect for flight.
0:27:46 > 0:27:50The lamb bone matches her own bodyweight,
0:27:50 > 0:27:54but the early-afternoon thermals create an invisible elevator,
0:27:54 > 0:27:55making flight possible.
0:28:19 > 0:28:22At any other time, this manoeuvre would prove dangerous
0:28:22 > 0:28:24and costly in energy.
0:28:29 > 0:28:32But by seizing her chance, she's been rewarded.
0:28:43 > 0:28:44Delicious.
0:28:59 > 0:29:03While the lammergeyer rides early-afternoon thermals
0:29:03 > 0:29:04close to the Equator...
0:29:06 > 0:29:09..a polar bear, right at the top of the Earth,
0:29:09 > 0:29:11is facing a very different challenge.
0:29:17 > 0:29:19Because of the tilt of the Earth on its axis,
0:29:19 > 0:29:23the Arctic summer is filled with almost endless light.
0:29:39 > 0:29:42Hunting seals under the sea ice, he's in no rush.
0:29:48 > 0:29:49At three o'clock in the afternoon,
0:29:49 > 0:29:52the sun is still high in the sky...
0:29:55 > 0:29:58..but the radiant heat from days of endless summer
0:29:58 > 0:30:00is melting his Arctic world.
0:31:27 > 0:31:31The sun will stay high over the Arctic for another two months.
0:31:31 > 0:31:34Soon, there'll be no ice left to hunt on.
0:31:34 > 0:31:37He will have to fast until the seasons change again.
0:31:42 > 0:31:44It's this seasonal journey of the sun in the sky
0:31:44 > 0:31:47that causes the greatest movement
0:31:47 > 0:31:49of animals across the planet.
0:32:24 > 0:32:27Driven by changes in weather,
0:32:27 > 0:32:28by opportunity,
0:32:28 > 0:32:30and danger,
0:32:30 > 0:32:32migrants criss-cross the planet.
0:32:35 > 0:32:38Across continents and through oceans.
0:32:39 > 0:32:44WHALE SINGS
0:32:46 > 0:32:49Even the lives of the greatest travellers are ruled by the sun.
0:32:57 > 0:32:58This family of humpback whales
0:32:58 > 0:33:01spent the winter breeding in tropical waters...
0:33:04 > 0:33:07..which made the perfect nursery for the new calf...
0:33:10 > 0:33:13..but are low on stocks of krill and small fish,
0:33:13 > 0:33:17the things 30-tonne adults like to eat.
0:33:21 > 0:33:25The calf is now strong enough to swim the 3,000 miles north
0:33:25 > 0:33:28towards the family's next big meal.
0:33:56 > 0:34:00Navigating across thousands of miles of featureless ocean
0:34:00 > 0:34:02is an incredible challenge.
0:34:03 > 0:34:05And with the adults running on empty,
0:34:05 > 0:34:07they can't afford to get lost.
0:34:09 > 0:34:11But the sun throws them a lifeline.
0:34:15 > 0:34:18Humpbacks are expert navigators.
0:34:28 > 0:34:30They use the sun to keep their bearings.
0:34:35 > 0:34:37Its changing position in the sky,
0:34:37 > 0:34:41combined with information sensed from the Earth's magnetic field,
0:34:41 > 0:34:43creates a reliable compass.
0:34:52 > 0:34:55So effective is their reckoning
0:34:55 > 0:34:59that between sunrise and this point in the afternoon,
0:34:59 > 0:35:02the family will have deviated less than one degree
0:35:02 > 0:35:03from last year's course.
0:35:14 > 0:35:16Late afternoon.
0:35:18 > 0:35:21The sun's time in the sky is running out.
0:35:21 > 0:35:23Its power is fading.
0:35:29 > 0:35:31Animals face an urgent new challenge -
0:35:31 > 0:35:34to make the most of the remaining light and warmth
0:35:34 > 0:35:36before it disappears.
0:35:44 > 0:35:47Back in Namibia, the sand is beginning to cool...
0:35:50 > 0:35:54..and the chameleon has undergone his most bizarre transformation yet.
0:36:01 > 0:36:04He's split himself right down the middle.
0:36:14 > 0:36:16Black side faced towards the sun
0:36:16 > 0:36:19to absorb every last bit of remaining warmth.
0:36:24 > 0:36:27White in the shade, to stop his body heat being lost.
0:36:35 > 0:36:36Being two chameleons at once
0:36:36 > 0:36:39will help him survive the cold night ahead.
0:36:46 > 0:36:49And he's not the only animal torn between the heat of the day
0:36:49 > 0:36:51and a chilly desert night.
0:36:59 > 0:37:01In the mountains of Oman,
0:37:01 > 0:37:02a rock hyrax family
0:37:02 > 0:37:06are soaking up all the late-afternoon heat they can get.
0:37:10 > 0:37:12They could also be accused of having
0:37:12 > 0:37:14a bit of an identity problem.
0:37:23 > 0:37:25Hyrax look like rodents,
0:37:25 > 0:37:29but their closest relative is actually an elephant.
0:37:35 > 0:37:37And although they're mammals,
0:37:37 > 0:37:39they need to bask to keep warm,
0:37:39 > 0:37:41just like lizards.
0:37:44 > 0:37:47Sunbathing in the late afternoon is a serious business.
0:37:51 > 0:37:55Every extra minute spent absorbing warmth from the rocks
0:37:55 > 0:37:57gives them a better chance of surviving
0:37:57 > 0:37:58the cold night ahead.
0:38:01 > 0:38:04But stretching out in the open like this is dangerous.
0:38:07 > 0:38:10They've no choice but to make themselves targets.
0:38:13 > 0:38:16And stonebaked hyrax is a black eagle favourite.
0:38:20 > 0:38:22The family are on high alert.
0:38:29 > 0:38:32The eagle's only chance is a stealth attack...
0:38:35 > 0:38:38..and the afternoon sun provides the perfect disguise.
0:38:39 > 0:38:42Diving at the same angle,
0:38:42 > 0:38:46the glare is an invisibility cloak.
0:38:48 > 0:38:50But hyrax have a unique adaptation.
0:38:52 > 0:38:53In their eye,
0:38:53 > 0:38:57the coloured iris slightly shields the top of the pupil.
0:38:59 > 0:39:01An in-built sun visor,
0:39:01 > 0:39:03perfect for eagle spotting.
0:39:15 > 0:39:18There won't be hyrax on the menu tonight.
0:39:27 > 0:39:30There's less than two hours left before sunset.
0:39:32 > 0:39:34The sun has lost its strength,
0:39:34 > 0:39:37but it has not lost its grip on our planet.
0:39:38 > 0:39:41It has one last hand to play.
0:39:49 > 0:39:51The phenomenal energy absorbed by the ground
0:39:51 > 0:39:53during the hottest parts of the day
0:39:53 > 0:39:55is released back into the atmosphere.
0:39:59 > 0:40:02Fast-rising, unstable, hot air
0:40:02 > 0:40:04colliding with higher, colder air
0:40:04 > 0:40:06creates weather.
0:40:06 > 0:40:09THUNDER ROARS
0:40:35 > 0:40:37If you live near the Equator,
0:40:37 > 0:40:39rain in the afternoon is just something you've got to put up with.
0:41:10 > 0:41:13A waterproof makes it all much more bearable.
0:41:15 > 0:41:16Although...
0:41:16 > 0:41:17this young orangutan
0:41:17 > 0:41:20hasn't quite got the hang of making his just yet.
0:41:34 > 0:41:36But over drier parts of our planet,
0:41:36 > 0:41:40all this pent-up heat energy can spell disaster.
0:41:47 > 0:41:49Turbulent air creates static charges.
0:41:53 > 0:41:55Lightning.
0:41:56 > 0:42:00Each strike five times hotter than the surface of the sun.
0:42:12 > 0:42:15Parched forests take like tinder to a match.
0:42:29 > 0:42:32The fire will eventually burn itself out,
0:42:32 > 0:42:34but the smoke lingers,
0:42:34 > 0:42:39scattering all but the very longest wavelengths of light -
0:42:39 > 0:42:41reds and oranges.
0:42:43 > 0:42:45While the Earth smoulders,
0:42:45 > 0:42:47the sunset burns extra deep.
0:42:54 > 0:42:57It takes, on average, just two minutes
0:42:57 > 0:42:59for the sun to sink below the horizon.
0:43:02 > 0:43:06Such a short time, in which everything changes for life on Earth.
0:43:17 > 0:43:19The sun's great energy,
0:43:19 > 0:43:23its light and heat, is suddenly lost.
0:43:31 > 0:43:34All over our planet, families regroup
0:43:34 > 0:43:36and find the safety of their beds...
0:43:40 > 0:43:43..as drowsy hormones flood back into their bodies,
0:43:43 > 0:43:45pulling them into sleep.
0:43:51 > 0:43:55But not everyone's quite ready to let the day go.
0:43:57 > 0:44:00Above a limestone cave in Borneo,
0:44:00 > 0:44:02a hawk, a day flyer,
0:44:02 > 0:44:04has not yet flown to its roost.
0:44:07 > 0:44:10What it's waiting for is just beginning to stir.
0:44:23 > 0:44:26Inside the cave, a storm is brewing.
0:44:38 > 0:44:41The beating wings of millions of wrinkle-lipped bats.
0:44:52 > 0:44:54They use sound more than sight to navigate,
0:44:54 > 0:44:56so leaving the cave before dark
0:44:56 > 0:44:58won't help them find food.
0:45:01 > 0:45:03But there's just so many of them
0:45:03 > 0:45:06that flying any later would cut into valuable feeding time.
0:45:26 > 0:45:30By pushing out into this last, brief window of light,
0:45:30 > 0:45:32they're taking a huge risk.
0:45:36 > 0:45:38The hawk is just one of many
0:45:38 > 0:45:39that's ready for them.
0:45:55 > 0:45:57Our eyes would struggle in this twilight.
0:45:59 > 0:46:02But the hawk's eyes can pick out fast-moving objects
0:46:02 > 0:46:04in the faintest glimmer of light.
0:46:17 > 0:46:20It's a twilight battle of the senses -
0:46:20 > 0:46:21sonar versus eyesight.
0:46:29 > 0:46:32In the last moments before complete blackness,
0:46:32 > 0:46:34eyesight still wins.
0:47:14 > 0:47:18As the very last of the sun's rays are lost behind the horizon...
0:47:20 > 0:47:24..for the first time, the planet is in true darkness.
0:47:28 > 0:47:29The night-time world.
0:47:41 > 0:47:46The darkness holds allure for a whole host of permanent night dwellers.
0:47:59 > 0:48:02They've acquired very different senses...
0:48:02 > 0:48:04that don't rely on sunlight.
0:48:12 > 0:48:16This scorpion has spent the daylight hours hiding deep in crevices,
0:48:16 > 0:48:18to avoid being eaten.
0:48:24 > 0:48:28But when the sun is quite absent, she becomes the predator.
0:48:42 > 0:48:45Her small eyes are all but useless in the darkness.
0:48:46 > 0:48:50Instead, she senses prey through vibrations.
0:48:50 > 0:48:54VIBRATIONS PULSE
0:48:56 > 0:48:58The movement of a single grain of sand
0:48:58 > 0:49:01gives her all the information she needs to attack.
0:49:14 > 0:49:16But just as she closes in on
0:49:16 > 0:49:19her first meal of the night,
0:49:19 > 0:49:20she freezes.
0:49:22 > 0:49:24Sensing danger.
0:49:28 > 0:49:30Even in the dead of night,
0:49:30 > 0:49:33our sun is still not lost.
0:49:38 > 0:49:40Its rays pass by the dark side of the Earth...
0:49:44 > 0:49:46..and reflect off its moon.
0:49:59 > 0:50:01A ghost sun.
0:50:09 > 0:50:12The full moon rises high and bright...
0:50:16 > 0:50:20..and the scorpion begins to glow.
0:50:34 > 0:50:37Ultraviolet light reacts with fluorescent chemicals
0:50:37 > 0:50:39in the scorpion's armour.
0:50:44 > 0:50:48Her eyes can't see moonlight, but her whole body is a warning system,
0:50:48 > 0:50:50telling her that her cover is blown.
0:50:53 > 0:50:56She needs to hide, before a predator sees her.
0:50:57 > 0:51:00So she uses the fluorescence to her advantage...
0:51:04 > 0:51:06..as a light sensor.
0:51:12 > 0:51:15Any part of her armour in shadow will stop glowing...
0:51:22 > 0:51:24..telling her she's found safety.
0:51:34 > 0:51:37The scorpion is not alone in her fear of the moon.
0:51:41 > 0:51:44Known as lunar phobia,
0:51:44 > 0:51:48many nocturnal species around the world will hide away...
0:51:52 > 0:51:54..and choose to go hungry,
0:51:54 > 0:51:56rather than risk coming out
0:51:56 > 0:51:58under the reflected sunlight.
0:52:06 > 0:52:09But to a hunter in Southeast Asia,
0:52:09 > 0:52:13a bright-lit night is an opportunity to be seized.
0:52:24 > 0:52:28Every night, the rainforest's insect population comes under attack
0:52:28 > 0:52:31from a palm-sized primate.
0:52:39 > 0:52:42Don't let the wide eyes fool you,
0:52:42 > 0:52:45this family of spectral tarsiers are ruthless hunters.
0:52:57 > 0:53:00With saucer-like eyes, each as big as their brain,
0:53:00 > 0:53:02this family use the faintest of starlight
0:53:02 > 0:53:05to see the forest in incredible detail.
0:53:22 > 0:53:24And when your eyes are this sensitive,
0:53:24 > 0:53:27all this reflected sunlight is a gift.
0:53:43 > 0:53:45The family aren't about to miss a moment of
0:53:45 > 0:53:47the best hunting night of the month.
0:53:57 > 0:54:01In the moonlit forest, the family might triple their hunting success.
0:54:08 > 0:54:10But it's all too easy for a tarsier
0:54:10 > 0:54:13to have eyes bigger than its stomach.
0:54:17 > 0:54:19In the early hours, full to bursting,
0:54:19 > 0:54:21the family call it a night.
0:54:32 > 0:54:34It's nearly morning.
0:54:35 > 0:54:38The moon is hanging just above the horizon.
0:54:39 > 0:54:42Soon, it will be overwhelmed by the first light of dawn.
0:54:50 > 0:54:53But in the Arctic, the sun is casting
0:54:53 > 0:54:57a new and different power over the last few hours of darkness.
0:55:02 > 0:55:07Particles thrown from the sun's surface across 90 million miles
0:55:07 > 0:55:09of empty space, to reach the Earth.
0:55:14 > 0:55:18They are directed by the Earth's magnetic field to the poles.
0:55:21 > 0:55:24This cosmic storm creates a magical aurora.
0:55:28 > 0:55:31The spectacular Northern Lights.
0:55:37 > 0:55:39But behind this beautiful light show...
0:55:41 > 0:55:43..is a sinister force...
0:55:52 > 0:55:57..that impacts on whales, with potentially lethal consequences.
0:56:01 > 0:56:05The humpbacks have been relying on the Earth's magnetic field
0:56:05 > 0:56:09to chart their night-time course.
0:56:09 > 0:56:10WHALE SONG
0:56:21 > 0:56:24But the Earth's magnetism is becoming distorted
0:56:24 > 0:56:26under this barrage of solar energy.
0:56:36 > 0:56:39It's believed whales can become disorientated.
0:56:45 > 0:56:46Thrown off course.
0:56:49 > 0:56:51They might even strand onto the land.
0:56:56 > 0:56:59But soon, it will be morning,
0:56:59 > 0:57:02and the sun compass will bring them back on track.
0:57:29 > 0:57:30Dawn.
0:57:32 > 0:57:35The very first light of a new day.
0:57:40 > 0:57:43The sun's power will soon be felt...
0:57:47 > 0:57:49..and the world is waking...
0:57:52 > 0:57:55..ready to begin another ordinary day...
0:57:56 > 0:57:59..on our extraordinary planet.