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25 years ago, this was the view
astronomers had of the cosmos.

Then came the Hubble
Space Telescope.

Suddenly, the true wonder of the
universe appeared before our eyes.

Delicate structures, vivid colours

and objects of staggering beauty.

Tonight, we celebrate a telescope
that has changed our view of

the universe as we reveal The Sky
At Night's top five Hubble images.

Welcome to the
Herstmonceux Observatory,

former home to the
Royal Observatory Greenwich.

The story of this place plays a part
in the story of how

the Hubble Space Telescope
came to be.

It was all about astronomers' search
for the best views of the cosmos.

The domes behind us contain four of
the largest telescopes in Britain,

moved here from Greenwich
in the 1950s and '60s.

They came to escape
the city lights and get

a better view of the night sky.

But soon, it was realised that even
this remote site wasn't good enough.

Observing was
limited by the British weather.

The ultimate site for astronomy
is up above the Earth's atmosphere,

getting away from its distorting
effects altogether.

And that was achieved when Hubble
entered orbit 25 years ago.

Coming up, how Hubble
came close to disaster.

Chris Riley investigates.

NASA's entire credibility

and that of the whole US space
programme was called into question.

Pete reveals how you can take
your own Hubble images.

Beautiful.
It's the Horsehead Nebula.

And we will reveal
The Sky At Night's number one

image from the world's pre-eminent
space observatory.

To compile our top five,

each member of The Sky At Night team
voted for their favourite images.

We tallied the results and it comes
up with a very varied list.

The top five includes images
that are inspiring and beautiful,

but also those that have pushed
science to new boundaries, expanding

our knowledge of the universe
in surprising and profound ways.

So let's get started
and see what is in our top five.

In at number five is
a Hubble classic.

An image that captures the remnants
of a dead star, the Crab Nebula.

This image was
captured by Hubble in 1999

and it shows a special
kind of nebula, a supernova remnant,

all that remains of a star that
exploded centuries ago.

The complex structure is
the result of a shock wave expanding

at 1,000 kilometres per second,
carrying gas and dust along with it.

As with many Hubble images,
the colours that you see

here aren't the ones you'd see
with your own eyes,

but they are meaningful -

they represent what Hubble sees in
different wavelengths of light.

But there's more to this image.
Hidden in the heart

of the nebula is a pulsar,
the dense, rotating core

of the star that exploded.

It's only 12 miles wide and it's got
a mass greater than that of the sun.

It's the astonishing
resolution of Hubble's cameras

that let us pick out
these fine details.

I still find it remarkable that
Hubble can show us

things moving
in an object like the Crab Nebula.

Here we can see cloud scudding
across an area three or four times

larger than our own solar system.

And, of course,
it's not just the Crab,

Hubble has looked at many supernova
remnants over the years.

Today, we take Hubble's
extraordinary images for granted,

but when the telescope was first
launched, it was rocked by

a series of disasters that
threatened to turn Hubble

into a billion-dollar flop.

Space historian Chris Riley
investigates how NASA

set about saving
Hubble from the jaws of disaster.

T-minus six, five, four...

On 24 April, 1990,

the Hubble Space Telescope was
launched from Cape Canaveral...

And lift off of the space shuttle
Discovery

with the Hubble Space Telescope,
our window on the universe.

..and placed into orbit
550km above the Earth.

Back on the ground, scientists
eagerly awaited the first images.

But as they came in,
it was clear something was wrong.

Instead of the sharpest, clearest
images ever taken of the universe,

Hubble sent back
a series of blurry shots.

An investigation was
immediately launched.

To everyone's horror,

it revealed that the fault lay with
the giant primary mirror, the most

important component of the telescope
and the most difficult to fix.

It might seem hard to believe now

but Hubble's flaw was so fundamental

in nature, this was such a basic

failure of project management,
that NASA's entire credibility

and that of the whole
US space programme

was called into question

and the agency came
under immense pressure

to try and repair the telescope

and its own reputation.

The mirror on Hubble plays the same
role as a lens,

magnifying and focusing the light.

To work, it needed to be perfect

but despite almost three years'
polishing, it had a slight flaw.

I've come to UK telescope-mirror
manufacturer Zeeko to find out

what happened to Hubble.

So what went wrong
with Hubble's mirror?

The mirror itself was polished well,

the machine that did
the polishing was good.

It was the measurement of the mirror
was not correct, so this resulted in

a perfect mirror, almost - it was a
very, very high-quality result they

achieved - but the shape of the
mirror was wrong, which means that

the rays coming from the stars
in the cosmos were not focused

to a fine enough image.

On Earth, the standard way to fix
the mirror would be to repolish it

but that was impossible in orbit.
A completely new fix was needed.

The solution was ingenious.

What the scientists realised was
that if they could recreate

the flaw in Hubble's
primary mirror - but in reverse -

perhaps they could cancel out the
effect and produce focused images.

So they built a new camera with
four tiny relay mirrors, all with

this reversed flaw incorporated.

For the engineers,
this was a painful process -

they'd never had to design something
that was intentionally flawed.

The same principle used to fix
the camera was also employed

to create a totally new device,
one which would correct

the light for all the other
instruments on board Hubble.

It was precision engineering
but, of course,

all this equipment was
constructed on Earth.

Now it needed to leave the planet
and join Hubble in space.

Repairing Hubble would require
one of the most audacious

space-shuttle missions
ever conceived -

five long spacewalks would be
conducted over five consecutive days.

In terms of complexity and ambition,

nothing like this had ever
been attempted.

To pull it off, the NASA astronauts
spent over a year undertaking

the most immersive
training programme to date.

Telescope mock-ups were
submerged in a neutral-buoyancy tank.

Logging more than 200 hours
underwater,

the astronauts repeated the hundreds
of complicated manoeuvres

required to fix the telescope
until they became instinctive.

'Five, four...'

On the 2nd of December 1993, the
mission to repair Hubble launched.

'And we have liftoff.'

'Hello, Houston,
let's go fix this thing.'

Two days later,
astronauts Jeff Hoffman

and Story Musgrave
stepped out the door.

Going out the door...

It is just awesome.
I mean, it is flat frightening

and I was scared.

I was scared preflight
and I was scared in-flight.

Cocooned inside their spacesuits
to do this repair work was

an exhausting task and handling tools
through their thick

spacesuit gloves,
like this Russian one here

at the National Space Centre
in Leicester,

was likened by astronaut
Jeff Hoffman to doing

brain surgery whilst wearing welders'
gloves, and I can see what he means.

It's very hard to get any sensation
of touch through your fingertips

and doing any dextrous, fine work
must have been close to impossible.

Spacewalks are never routine

and the Hubble rescue mission was
going to be harder than most.

There was already a serious concern

when it came to installing
the new optical device...

..a process that had been problematic
in training, as the mock-up

didn't quite fit.

Would the same problem occur
with the real telescope?

It was just kind of cross
your fingers, hope things were built

according to the way the drawing
said they were built,

that no changes were made
after the drawings

and that the thermal environment it
was in hadn't changed anything.

Back on the ground, the team
at mission control held their breath.

Carefully, astronaut Kathy Thornton

manoeuvred the new optical device
into place.

It's a very big box
going in a very small hole

with about an inch of clearance
going in and then, obviously,

the clearances got tighter.

Thankfully, it was a perfect fit.

Good work, guys.

But something else,
completely unforeseen,

put everything in jeopardy.

A simple service hatch
refused to close.

'Copy.'

Even the slightest chink of light
getting inside the telescope

would render it useless.

The astronauts had to get
the latch to lock.

'Houston, if you copy, Jeff's just
working on putting the doors

'back together and thinks he's found
a way that seems to close the gap

'and we're going to try that,
if that's OK.

'Press on, if you've got a way
to do it, do it.'

Using a strap and a ratchet,

a free-floating Story Musgrave
improvised a solution.

It was a success.
The astronauts were elated.

But now scientists on the ground had
to wait for the first images.

On New Year's Eve 1993,
they came in.

CHEERING

Oh! Whoa! We did it!

What was a blur was now
crystal-clear

and our view of the cosmos
was changed for ever.

Now, back to our countdown.

Number four is
occupied by the Carina Nebula.

It's located in the
southern-hemisphere constellation

of the same name.

To Hubble's eyes, it looked
more like a Turner painting than

a photograph of
a real phenomenon.

The Carina Nebula is a huge
cloud of dust and gas,

some 300 light years across.

That's seven-and-a-half times
the size of the Orion Nebula.

This massive tumultuous cloud is
essentially a giant stellar nursery.

Now, Hubble has taken many striking
images of nebulae like this,

including the iconic
Pillars of Creation

or the Horsehead Nebula, which
nearly made it into our top five

in their own right.

But the Carina Nebula is one of
the biggest star-formation regions

in the galaxy,
which makes it the perfect

laboratory for studying
the birth of stars.

A composite of 48 frames taken by

Hubble's Advanced Camera
for Surveys,

reveals unique detail giving us

a treasure-trove of amazing
astronomical objects.

There is Eta Carinae, a star system
and nebula in its own right

that houses one of the most
massive stars documented.

And there are the astonishing
silhouettes of dark dust pillars

backlit by the brightly shining gas.

It's all here in the Carina Nebula.

On with the countdown.

The image with the third-most votes
from the Sky At Night team

is the Hubble Deep Field.

Taken in 1995, Hubble was pointed
for ten days at a patch of sky

that appeared to be empty.

Instead, it revealed an area teeming
with ancient galaxies.

The Hubble Deep Field has been
described as one of the most

important images ever taken
because it gives us

an understanding of the scope
of our amazing universe.

What makes the Deep Field so
revolutionary is that it allows us

to look back in time,
over 12 billion years,

to the very early universe.

Chris is speaking to Sarah Kendrew,
looking at the impact of these

Deep Field images.

So, Sarah, tell us how
the Hubble Deep Field came about.

The Hubble Deep Field...
Scientists had

basically proposed to look at an

empty patch of sky, so that's quite

an unusual thing to want to do.

It seems crazy.

Right, because they had no idea what
they were going to find,

so it's quite hard to justify but
ended up being incredibly successful

and became the iconic image
for the Hubble Space Telescope.

Yeah, I was just going to use that
word, it really is a stunning image.

We can look at it here. What exactly
are we seeing in the Deep Field?

So, it's a relatively small patch
of the sky that was specifically

selected for not having many
sort of stars in the galaxy

in the foreground but what
we can see is that all this light

comes out from the background

and every single point of light in
this image is an individual galaxy.

But, of course, this isn't the local
universe, so we're seeing

these galaxies as they were many
billions of years ago, as well.

That's correct. We have a whole
range of galaxies in this image.

Some of them are nearer to us

but we are also probing
down to the first billion years

of the universe's existence
and that really was very new.

It really gave us, for the first
time, this quite large

sample of galaxies from
the very early universe.

And we can take a closer look
at them.

The Ultra Deep Field,
which came a bit later,

was sort of the improved version

but these galaxies look different
than the ones we'd see today.

That's right and that's one
of the main outcomes

of the Hubble Deep Field.

Galaxies in the early universe,
you know,

have quite a different appearance.

Whereas the galaxies we see
in the universe today tend to be

quite ordered - they have a nice
spiral shape

or they're blobby,
elliptical galaxies -

these are much more irregularly
shaped, so you can see,

for example, some galaxies
that are merging together.

And that makes sense

because the universe was much
smaller in those early days

before the expansion had really
grown it to a larger size,

so the small galaxies were
more densely packed

and so they would collide to then
sort of form bigger structures,

so that's really
an outcome of this image.

So why couldn't you do
this from the ground?

Why do you need a space telescope
to take this sort of Deep Field?

Well, the problem we have
on the ground is that the Earth

is surrounded by the atmosphere,
which is basically a dense

coating of turbulent gas
and that really distorts light as it

comes in from space and so it's very
hard to get images with this kind of

fine detail that we can see
with the Hubble Space Telescope.

We get a blurred view
from the ground.

We get a very blurred view.
Especially over very long exposures,

the light would become quite blurred

and you don't get these beautiful
images and that was really

very new for
the Hubble Space Telescope

to be able to achieve this.

Hubble will be around
a little while yet

but it is coming to the end of its
life, what comes next?

So, the successor to the Hubble
Space Telescope is getting

really close to its launch now.

It's called
the James Webb Space Telescope.

It's a much bigger
telescope than Hubble.

So its mirror has a collecting area
that's seven times larger

than that of Hubble, so it's just
going to be able to catch

an awful lot more light than Hubble.

Specifically, to be able to
push further into the early universe

and see the very first
galaxies that formed.

And to do that, it has to
work in the infrared.

That's right, because the light
from distant galaxies gets

stretched to longer wavelengths,
so to be able to observe further

and further back in time,
we need to be able to go further

and further also
along in wavelengths.

You mentioned that you're involved
in one of the instruments for

James Webb and that gives you
some say

in what the telescope might look at.

What are you particularly
excited about seeing?

What I'm particularly interested in
is looking at the galaxies

that are a bit nearer to us.

We already know these
galaxies are there

and we know that they are forming
stars at an incredibly

vigorous rate, so that's something
that'll be very exciting,

to really see how that star
formation is triggered

and how it's shut down
and how these galaxies are

sort of converting
their material into new stars.

Well, we'll look forward
to seeing the results.

Sarah, thank you very much.
Thanks, so do I.

Still to come, we reveal our
number one Hubble image.

But first, Pete is here
with his guide to taking your own

versions of iconic Hubble images.

Hubble certainly takes
some of the best

and most spectacular
images of the cosmos

but many of its iconic targets are
also within reach of amateurs too.

Take the Orion Nebula.

It can be amazing through a telescope

and is easy to photograph with
a stills camera.

Orion is now heading out of view,
so how about creating your own

version of the famous Pillars of
Creation by imaging the Eagle Nebula?

You can see the famous Pillars
here in this image

and they are the features which gave
the Eagle Nebula its name.

The one in the centre is supposed
to represent the Eagle's body,

then we've got the wing down here and
he's carrying a fish up to the sky.

Now, marvellous though the colours
are that we're looking at here,

they're not the colours you'd
see with the human eye

but, rather,
they're peculiar to the way

that Hubble images are constructed.

Hubble takes images
in a very particular way.

Its cameras are actually
black and white,

so to create a colour image,
Hubble takes multiple shots

of the same object through
different filters.

Each are assigned a colour.

When combined, they create a rather
distinctive colour scheme,

known as the Hubble Palette,

and it's possible to do this
yourself with the right filters.

The aim here is not to try
and create a photograph which looks

natural to the human eye but, rather,
to create one which picks out

features emphasised by certain
elements.

Now, to demonstrate how striking
this effect can be, here is

a Hubble Palette version of the
Rosette Nebula and you can see lots

and lots of fine,
intricate detail here.

If I switch to the normal view,
you see a lot of that detail is lost.

I've come to meet some of the members

of the Breckland Astronomical
Society,

who've been capturing some
iconic Hubble targets.

Richard. Hello. Ah, that's a very
recognisable object there.

That's the Crab Nebula, isn't it?

Yes, it is, yes, yes.

So, did you take that?
Yeah, I took that myself,

just with my amateur kit.

Well, that's, I mean,
that's a great result, isn't it?

That's...you got loads of detail
in there, loads of little filaments

and whatever. I mean,
Hubble obviously does it better.

Of course. But that is quite
something for somebody to grab.

Ah, yes, this is the one I've been
looking for. It's beautiful.

The Horsehead Nebula,
and the Flame Nebula there, as well.

Incredible, cos I remember the first
time I ever took a photograph of this

region, looking for the horse's head,
and it's difficult to see it.

It's just there,
hiding in the background.

But to actually tease it out,
and bring it out...

That's right, I remember

the first time I imaged it, as well,

and it was just barely visible.

Right, OK. With the equipment now,

it's fairly easy.

Thank you very much, Malcolm.
Thank you.

Amazingly, these days it's even
possible for serious amateurs

to have a go at recreating
the Hubble Deep Field,

which makes a nice challenge.

I want you to go out,
if you've got serious kit,

and try and get a photograph
of that iconic area of the sky.

And see what you get back.

If you do get anything,
then send it up to our Flickr group,

which is at...

And we'll put the best ones
in a gallery.

So if you fancy having a go
at imaging the Hubble Deep Field,

here's how to find it.

First, locate the Plough.

Imagine an equilateral triangle

using the stars Megrez and Alioth
at its base.

The triangle points to two stars

on the threshold
of naked-eye visibility.

We've marked these as A and B.

Extend the line from A through B,
for the same distance again.

Now, turn by a right angle
and head down towards the Plough.

This points to a patch of sky
with nothing in it,

and it's the location
of the Hubble Deep Field.

Back to our countdown,
and we've reached number two.

A striking image of the largest
planet in the solar system, Jupiter.

And amongst its bands and spots
can be seen several dark marks -

scars from the impact
of Comet Shoemaker-Levy 9.

I always like to think of Jupiter
as our big brother in space.

It's absolutely enormous -
300 times the mass of Earth.

And it's that enormous mass
that absorbs some of the impacts

that could otherwise
wipe out our existence.

That was theory, until we saw
these amazing images,

which showed the impacts

that our big brother
is absorbing on our behalf.

In July 1994, 21 fragments of
what was the Comet Shoemaker-Levy 9

crashed into the atmosphere
of Jupiter,

and Hubble was on hand
to witness the event.

The impacts happened just over
the limb, on the planet's far side,

though the plumes
were detected from Earth.

But the true enormity of
what had happened

became apparent slightly afterwards,

as Jupiter rotated, bringing
the impact sites into Hubble's view.

The wonderful thing about this event

was that no-one had any real idea
what to expect.

We hoped we might see the impacts
with Hubble, but that was about it.

And I remember going outside
with my own small telescope

and being able to see these bruises
on Jupiter's surface.

And then to see the Hubble images

afterwards made for a really
thrilling event.

The resulting impacts were more
profound than anyone had predicted.

Using different
wavelengths of light,

Hubble captured striking
images of the impact scars,

revealing some to be
twice the size of Earth.

These images turned out to be
a boon for scientists,

because they dragged out chemicals
from deep below, and gave us

a window into Jupiter's atmosphere.

We're reaching
the end of our countdown,

but we still want to hear
about your favourite Hubble images.

So send us your selection
via Twitter,

using the hashtag #hubbletop5.

Before we reveal our number one,

here's a recap of
The Sky At Night's top five.

At number five

is the dying embers
of an exploding star -

the Crab Nebula.

At number four, that kaleidoscope
of colour - the Carina Nebula.

Number three is a look back in time
with the Hubble Deep Field.

And at number two,
a comet's collision with Jupiter.

And that just
leaves our number one image.

It's an image I didn't think
would come out on top,

I don't think any of us did.

But it's this one...
V838 Monocerotis.

V838 is an extraordinary
evolving structure

in the constellation of Monoceros.

The light comes from a
mysterious outburst on a star,

which created a flash a million
times more luminous than the sun.

And what we're seeing is that light
bouncing off the surrounding dust -

what we call a "light echo".

There aren't many astronomical
objects that change

before your eyes, and few that do
so with such beauty and drama.

The source of the explosion

was a giant red star
that suddenly brightened.

And it's the journey that
that light took that captivates.

The flash occurred in 2002,

briefly making V838
the brightest star in the Milky Way.

Since then, the light has been
expanding outwards,

bouncing off rings of dust
surrounding the star.

We can actually see
the light of the explosion,

spreading out as
it illuminates the clouds around it.

What I love about
this sequence of images,

is that it reveals the hidden
side of space.

There's all this stuff,

all this dust out there
just waiting to be lit up.

And watching the sequence
also reminds us how long it takes

light to travel across the vast,
empty distances of space.

I find this object absolutely
captivating.

It looks as if it's expanding
right in front of our eyes,

even though it's just the light
travelling through.

But what caused this explosion,
and why does it look this way?

I've been speaking to
Jacco van Loon.

Jacco, these images of 838
are absolutely fantastic.

But can you tell me what's going on?

Well,
this is an object that erupted,

so, all of a sudden,
it became a bright object.

It lasted a couple of months
and then it faded.

Afterwards, it erupted again,
and once more after that.

And that's very unusual.

Usually you see a single explosion
and then it fades.

So, do you know a mechanism to
explain this sort of phenomena?

Yeah, various astronomers know
mechanisms. They don't all agree.

A mystery. They include, for
instance, the merger of two stars.

Another possibility is a nuclear
explosion inside a star, perhaps.

Or on the surface of a star.

So what has been left behind
after these multiple explosions?

Well, we can't see that at the moment
because shortly after

the eruption, there was
a very dense shell expanding.

But dust formed in it
and obscured whatever happens inside.

So, at the moment,

it's waiting for the dust to clear
and see what's left behind.

So, at some point, will we be able
to see, yes, what remains?

But on what sort of timescale?

Usually on astronomical levels,
things are pretty long.

Well, what remains,
if anything, of course...

We expect it to happen on timescales
of years. So, within our lifetime.

Well, it sounds fascinating,

and I can't wait to see
what lies behind the dust.

Thank you very much for talking
to me. You're welcome.

Hubble's expected to
remain operational

until at least 2020, so there's
plenty of great science to come.

And James Webb will provide
wonderful images

and science in the infrared,
but astronomers are already

planning for the next generation
of great optical space telescope.

But Hubble still has some
treats to come.

In the next few weeks,
the team has promised

the release of a special image to
celebrate the telescope's birthday.

So keep a lookout for that one.

Next month, we'll be exploring
our nearest neighbour, Venus,

and finding out what makes
Earth's twin

such a different place
from our own world.

Remember, send us your Hubble
top five to the Twitter account...

In the meantime,

get outside and get looking up.

Goodnight.