Script for the A-level Cosmology show made in collaboration with Karen Masters at ICG.
Start outside dome
After safety briefing introduce yourself
and your research. Introduce WAA and the Stellarium software/ apps. Introduce
Cosmology ‘ trying understand the nature of the Universe as a whole’ Cosmologists seek to understand the
origin,
evolution, structure, and
ultimate fate of the Universe at large, as well as the natural laws that keep it
in order. I actually studied an individual supermassive black hole in a galaxy
as part of my research, a cosmologist might also study supermassive black holes
but they would think about them in terms of ‘the part they have played in Galaxy
evolution in the universe as a whole’
5 mins
In dome
Play WAA 25 mins Play ‘Zoom through telescope’ Movie 1 min 17sec
Go into Stellarium
Finding North
Starting with Big dipper,
which is an asterism, part of the constellation ursa major, which means the
Great Bear. And Ursa Minor, which means
small bear. The lowest too stars in the saucepan point to North Star.
It looks like a saucepan, with a handle and
a place to put your beans, counting from the 2 stars at the end of the pan,
count in a straight line about 5/6 steps (at a step distance of the gap between
those 2 stars). There you will find Polaris aka the North star. Many people think North Star is the brightest
in the sky! It isn’t! it is only important because it is directly above the
North Pole, and stays above the north pole as the earth spins on its axis
causing all the other stars to spin around! Think about spinning top (from
Christmas cracker) the top part, which you spin around with your fingers,
doesn’t appear to move while the sides of the top are whizzing around. The
middle of the top represents the North Pole with the North Star is right above
it. Make sure they realise none of the stars actually move, and it’s us that
are moving?
(speed up time L in Stellarium so they
can see stars going around in arcs)
Mentioned Axis of Earth ( if time mention Southern
Hemisphere doesn’t have a star above south pole :( They use Southern Cross and
point to an area which is above/below the South Pole)
Constellations Make sure can see both Cass and big dipper
Ask ‘what is a constellation? ‘ Explain these are 48 constellations in
total.
Turn on constellation
art press ‘r’ key
Patterns of stars in sky, imagine the
ancient Greeks without TVs very bored so used to join the stars together like a
dot to dot, Mention that the Saucepan/Big Dipper is an Asterism not constellation, as it is part
of the great bear. Turn off constellation art r
Circumpolar stars
Explain that the
constellations of Cassiopeia and Andromeda and Ursa Major etc are Circumpolar
constellations and never set.
Cassiopeia
Cass looks like a W
or an M for McDonalds, find her from the Big Dipper by drawing a line through
North Star. Cass is a queen married to King Cepheus (he is in sky near by looks
like a house drawn by a child). Andromeda is
Cass’s daughter. Mention film ‘Clash of Titans’ and Greek Mythology but
don’t talk about it any further.
Zoom to Andromeda
Locate Andromeda.. go
along same line from Polaris, to Cass, and thru to Andromeda.. (Search Fn-F3
for M31, and zoom in using / in stellarium)
When in Andromeda
constellation, say it is our nearest spiral galaxy Andromeda (in local group.)
It is 2.6 million
light-years (2.5×1019 km) away. And it is the
most distant object you can see with the ‘naked eye’.
Andromeda looks a lot like our own galaxy and
you can imagine if you were flying in space outside our Milky Way it would like
very similar to Andromeda.
Andromeda is actually
has double the amount of stars that the MW has.
Dark matter in Andromeda
So I
just mentioned that Andromeda has more stars than the Milky Way. But
astronomers think that the Milky way is actually more massive, as it has more
Dark Matter. Can anyone tell me what dark matter is?
Vera Rubin is a scientist from the USA who studied the variation of the
velocities of the gas in between stars (interstellar medium) with distance from
the center of the galaxy. She found that …
Black hole in Andromeda.
Now it might shock you to know that our Solar System is orbiting
in our galaxy around a Supermassive black hole
And there is also a supermassive black
hole at the centre of Andromeda galaxy.
These supermassive BH were predicted by Einstein’s theory of
general relativity. They exist at the centre of all galaxies, a million times
that of sun. The BH in our MW is actually 4 million times mass of sun! Ask
‘how do you think astronomers know the mass? Cos they can’t just weigh it with
a scales?’ Using Keplers Third Law which hopefully you have heard of this
equation which relates the speed of stars which are orbiting the Mass, to the
mass of the thing they are orbiting. This is exactly how we measure the mass of
the Sun.
Astronomer measured high speeds of stars
orbiting around an object known as Sagittarius A* which is at the centre of our
galaxy the MW.
Can zoom / into Sagittarius A*/ search for Sagittarius using Fn-F3. Can’t
see much there, turn off the constellations , c and search fnF3 for M25
this is a near by cluster of stars
Explain
that at the centre of our galaxy astronomers measure the speeds and orbits of
stars just like that’s how they know there is a supermassive black hole there!
Ending
thought about black holes.
Most people think of black holes as
monsters but Astronomers now think they play a large part in the early
formation of galaxies. As we learn more about how galaxies were formed in early
universe it seems that the BH at the centre plays a large part in forming
galaxies, remember that the jet from the centre of the galaxy can reach into
other galaxies, these jets of particles might start star formation to occur in
galaxies where it might otherwise not have occurred. This means that without
our blackholes the universe might of not formed galaxies. And without galaxies
there wouldn’t be stars, without the stars, no solar systems of planets and
with out planets, no humans, so black holes may not something to be afraid of.
The massive Jets from galaxies like M87 and
3c273 are so far reaching that they can actually reach into nearby
galaxies. Astronomers think that these
jets can affect the surrounding galaxy giving the surrounding galaxies more
energy. This might mean that idea that black holes are monsters is wrong; they
actually might be responsible for the formation of galaxies like our own. And
of course without the galaxy there is no solar system and without the solar
system no place for us to live!
For example if our Sun turned into a black
hole we wouldn’t all get sucked in, the Earth would actually orbit around quite
happily. Obviously, without the energy from fusion humans would not exist
though.
Gravity works for black holes just like it
does for everything else. Black holes don’t suck – they just have very strong
gravity, so it’s dangerous to get very close. But far from a black hole things
orbit them normally.
Blueshift and redshift
Ask if they have
heard of red shift or doppler shift? Remind them that that it is to do with the
wavelength of electromagnetic radiation. When an object is moving away from you
(like most galaxies are moving away from us) the radiation or light we detect
is shifted to longer wavelengths because of the motion of the object away from
us means the light waves get stretched out, i.e. the energy of light measured
by an astronomer is nearer the lower energy red end of the spectrum , hence the
name ‘red shift’ – compare with the pitch of the ambulance siren as it goes
past you with the wavelets bunching up in front of the ambulance when it is
moving towards you, and spreading out behind. Sound wave compressed as it came
toward you, and stretched as it went away. Same is seen in stars, and used to
observed the motion of galaxies.
Say that the light from Andromeda is actually
blue shifted! Ask them what this means? So MW and Andromeda are actually moving
toward each other in space at about 100km per sec which seems very fast and
might scare you but this is actually equivalent to 400 lightyears every million years (and remember
Andromeda is 2.6 million light years away) attracted
to each other by gravitational forces due to their large masses, in 4.5 billion
years they will collide making a much larger galaxy.
Out of Stellarium
Play ‘Redshift blueshift’ movie 12.27-12:37 10 secs
You can see the light is redder or stretched
because the galaxy is moving away from us.
Galaxies come in different types. We’ve seen the
Milky Way and Andromeda which are both spiral galaxies, but we think after they
merge together they might form an elliptical galaxy which are the other kind.
Play ‘highresgalaxycollision’ movie 53secs
Lots of astronomers work to try to understand how
the different kinds of galaxies formed and how they got the shapes they have.
Now hopefully some of you have heard of the Galaxy
Zoo project. This is an site where members of the public, like yourselves can
help the astronomers by classifying galaxies. You do this by going on the
website and just looking at the shape of the galaxy to decide which type you
think it is.
Our view of the universe has changed.
It is only since the 1500’s that we have
really started to understand the solar system and our universe.
Play ‘Solar system models.mov’ 1 min 05:15-06.09
Before telescopes were invented everyone
believed the earth was the centre, we thought the sun, moon and planets orbited
around it.
Then in 1543 Nicholas Copernicus
proposed a different model with the Sun at the centre, it was a radical idea
and he didn’t have any evidence to prove it. Nearly 65 years later, Hans Lippershey
fixed 2 small pieces of glass into a tube and made an Eyeglass. Galileo saw
these designs and made his own telescope and observed Jupiter, and noticed some
points of light either side of Jupiter which appeared to move around it. He
soon discovered these were moons orbiting around Jupiter, and this made people
realize that the Earth wasn’t actually so important, since objects could
clearly orbit around other planets like Jupiter. The telescope was then used to
prove Copernicus’ new theory that the earth was not the center of the Universe.
It was also used to learn more about our Galaxy
Play ‘Galaxies.mov’ 1 min 48 12.37-14.33
Our Galaxy and Other Galaxies
We have only known that we have lived in a
galaxy for the last 100 years. Before the 20th century thought the
universe consisted of a flat disk of stars with the earth and the solar system
at the centre.
Caroline Herschel made a
map of this disk, but because telescopes did not have the resolving power of
todays telescopes. They thought the other galaxies were part of this disk. An
astronomer named Edwin Hubble observed Cephid Variables and was able to
determine that these galaxies were extremely far away.
There was a massive public debate in 1920
between two astronomers about if “spiral nebula” were external, or in our own
Galaxy. Harlow Shapley thought they were in our Galaxy because it was really
huge. Heber Curtis thought our Galaxy was smaller and the others were all
external. Turned out they were both right as the universe is much bigger than
they could imagine. Our Galaxy is as big as Shapley thought it was and the
others are all outside it!
An astronomer named Edwin Hubble observed
Cephid Variables in the mid 1920s and was able to determine that these galaxies
were extremely far away. He also used these measurements to show that the
further galaxies get from us the faster they are moving away from us (using
measurements of their redshift). This demonstrated that our Universe is not
only vast, but also expanding!
Play ‘Fly through HST galaxies’ 1 min 20.48-21:33
We now have such good telescopes (like the HST)
that we can see galaxies that are so far away that the light from them has
taken almost half of the age of the universe to reach us.
Light travels very fast – about 1 metre in 3ns,
but it still takes 8 minutes to reach us from the Sun, 3 years from the nearest
star, and millions or billions of years from the external galaxies.
These galaxies show an incredible variety of
different types of galaxies even very early on in the Universe.
Sloan Digital Sky Survey
Play Journey_3D_HD (on desktop) 1min 23sec
|
This visualization
presents a 3-D view of the largest structures in the Universe via data from
the Sloan Digital Sky Survey. The SDSS is the most ambitious astronomical
survey ever undertaken. It provides a 3-dimensional map of about a million
galaxies and quasars. As the survey progresses, the data are released to the
scientific community and the general public in annual increments.
|
We also have massive surveys of galaxies in the
Universe. This movies shows 1 million galaxies which have been mapped by the
Sloan Digital Sky survey.
We can’t see galaxies everywhere. These black
areas are the modern equivalent of “here be dragons” anything there is hidden
from our view by our own galaxy.
But the web like structure is real. This is
showing how galaxies formed where there were clumps of dark matter in a
filamentary web. We can understand things about cosmology from carefully
mapping the shapes seen in this structure.
When we look at the most distance galaxies, we
are looking further back into time. This is because the light from the most
distant galaxies has taken such a long time to get to us. Therefore, the
furthest point we want to look back to is the creation of the Universe, the
time of the ‘Big Bang’.
Each marker here is actually real data ,
which is why there is a big gap in this data. It doesn’t mean there aren’t
galaxies there; we just haven’t looked there yet.
Quasars are
thought to be the first massive structures which formed in the beginning of the
universe, half a billion years after big bang. In this data you can see a clustering
of the galaxies in certain areas. Astronomers think the reasons why quasars
seem to be surrounded by dense clusters of galaxies is because the jets from
these early quasars actually played a part in fuelling the formation of
galaxies.
The CMB represents the edge of observable
universe. When I say observable universe what I mean is there are galaxies and
quasars out beyond this boundary it is just that we cannot see them, remember
this is real data taken by telescopes and they can only observed the light from
galaxies out to a certain distance. Just like when you are in power cut with a
candle and can only see things right in front of you.
CMB
End with CMB on sky from movie
Beyond the quasars we have the light from
the Cosmic Microwave Background or CMB , this light marks the edge of
observable universe. This is not really the edge of the Universe but it is the
light from the very beginning of the universe 380,000 years after the Big Bang when
electron and protons started to form into hydrogen atoms...and we can’t see the
light from back any further than this
The CMB fills the universe almost uniformly. It
may not look like it from this image of the CMB but Astronomers
say that the CMB shows us that the Universe is Isotropic and Homogeneous Isotropric
means the same in all directions, and Homogeneous means the universe will look the
same from whatever position you stand in.
The CMB is at a temperature of 3 degrees above
absolute zero(or 3K)
And has a wavelength between the mm-cm regime, which
is comparable to radio and TV Wavelengths.
This means you can use your TV to detect
radiation from the big bang, if you tune a TV between channels about 1% of the
static is from the CMB.
These spots of different colour represent very
small fluctuations in the density of the CMB and it is in these most dense
regions where galaxies would have formed.
END
Take questions outside of dome for 5
mins….
