Earth’s Natural Satellite
The Moon
Earth & Space
SNC1D
Fun Moon Facts
•
A Blue moon occurs when two full moons occur in the
same calendar month (occurs once every 2.5 years)
• * The harvest moon is the full moon that occurs
closest to the date of the autumn equinox (Sept. 21) in
the Northern Hemisphere
• * A month with no full moon occurs only about 4 times a
century
• * It takes 60 to 70 hours to reach the moon by rocket
• * 12 men have walked on the moon
How was it formed?
Impact Theory:
This theory
suggests that an
object about the size
of Mars hit a fully
formed Earth. Matter
from Earth was flung
into space and
eventually clumped
together to form the
Moon.
Moon Mania
•
•
•
•
•
•
•
•
AKA:
Orbit:
Diameter:
Mass:
Luna
384, 400 km from Earth
3476 km (0.27 ED)
7.35 x 1022 kg
(0.01 x Earth’s mass)
Temp. Range:
- 163 oC to 117 oC
Avg. Surface Temp:
1 oC
Rotation Period:
27.3 days
Orbital Period:
27.3 days
Interesting Moon Fact
• Synchronous Orbit
The Moon always
shows us the same
face. Since the Moon
is rotating and orbiting
in the same amount
of time (27.3 days).
The Map of the Moon’s features
Lunar Features
The Moon is a Punching bag
• The Moon's heavily cratered surface is the result
of intense pummeling by space rocks between
4.1 billion and 3.8 billion years ago.
• The scars of this war, seen as craters, have not
eroded much for two main reasons: The Moon is
not geologically very active, so earthquakes,
volcanoes and mountain-building don't destroy
the landscape as they do on Earth; and with
virtually no atmosphere there is no wind or rain,
so very little surface erosion occurs.
Come Over to the ‘Dark Side’
• The far side of the
moon is often called
the ‘dark side’ of the
moon because we do
not see it. However, it
is not always the dark
side and thus should
be called the far side.
During a new moon
the far side is fully
exposed to the Sun’s
light.
Moon Phases
•
http://home.hiwaay.net/~krcool/Astro/mo
on/moonlif.htm
Weather on the Moon
• There is no weather on the Moon (i.e.no
rain, no wind) because the Moon does not
have an atmosphere. Without an
atmosphere it has no protection from the
Sun’s rays or meteorites. Also, it does not
retain the Sun’s heat.
• Temp. Range:
- 163 oC to 117 oC
• Avg. Surface Temp:
1 oC
Can you feel its pull?
• Gravity: 1/6th that of
Earth
Stars
Expectations: D2.3, D2.5,
The Formation of the Sun and the Solar
System
Solar Nebula Theory
• A solar system begins with a Nebula – a HUGE
cloud of gas and dust
• Gravity causes the material in the nebula to
spin together
• The pressure in the center creates heat – a
protostar is formed.
• The dust and gas spinning around clumps
together to make planets.
• Spinning nebula flattens into a disk shape
• Eventually the temperature of the protostar
reaches 10 000 000oC, and nuclear fusion
begins – a star is formed!
Our Growing Sun
• Our sun began as mostly hydrogen
• Nuclear fusion joins two hydrogens together to make
helium – this creates an amazing amount of heat and
light.
• Helium is denser than hydrogen and accumulates in the
central core. This is continually growing.
• As the temperature rises, the star grows in size, until it
reaches a balance between expansion and gravity (like
our Sun)
• The fusion of hydrogen in our sun can go on for about 10
billion years, right now our Sun is at the ½ way point – it
is about 5 billion years old.
Features of the Sun
• Photosphere
– The surface of the Sun
– Thousand of km deep
• Sunspots
– Strong magnetic fields
– Sunspots measure 4500oC whereas the Photosphere
is 6000oC.
– Bright areas that look dark because of the contrast in
temperature
• The Sun’s Rotation
– Movement of sunspots demonstrates it is rotating,
faster at its equator than at its poles.
Features of the Sun (cont’d)
• Solar Flares
– Groups of sunspots eject magnetic particles
into space = solar wind
– When the solar wind hits Earth create
currents that flow to the poles.
– We end up with a great show of green and/or
red light
– We see aurora borealis at the north pole and
aurora australis at the south pole.
How do Stars Differ?
•
•
•
•
•
•
Size
Mass
Brightness (Luminosity)
Composition
Temperature
Colour
Different Stars
More Massive Stars
Life Cycle of Stars
• Nebula: birthplace of
a star, made of gas
and dust
Nebula
• The life of a star is determined by its
mass.
• The more massive the star, the faster its
rate of nuclear fusion and therefore a
shorter life.
• Luminosity – the total amount of energy a
star radiates per second (J/s).
Hertzsprung-Russell Diagram
• An H-R Diagram is a
graph that plots stars
according to their
Temperature (x –
axis) and Luminosity
(y-axis)
• The stars plotted
along the curved
diagonal of the graph
is called the Main
Sequence on an H-R
Diagram
• There are 3 other
sections on the H-R
Diagram that stars
also appear in that
are categorized as
Red Giants, Red
Super Giants and
White Dwarfs
Red Giants
• Giants appear near the upper right section of the HR
Diagram
• Have a bigger radius than the stars of the same
temperature which gives them a higher luminosity
• Fuse Hydrogen on the shell, with an inactive
Helium core
• Gravity contracts and heats up the Helium
compressing the Hydrogen layer above causing a
faster fusion process which causes the star to
become more luminous and expand
Red Super Giants
• Red Super Giants appear in the upper right
section of this HR Diagram because they are
much cooler than stars of the
same luminosity, however they appear very
bright due to their massive size which
ranges from 200 -1000 times the radius of
our sun
White Dwarfs
• Appear in the lower left section of this HR
Diagram because they are extremely hot, yet
appear very dim due to their extremely small size
• Can be as small as .01 times the radius of our
sun
• Are the burned-out remains of stars like our Sun
and tend to be small because they have ran out
of nuclear fuel
• Can be so dense that gravity slows down the
light leaving the surface to make it appear redder
How do we really know what's out there?
Space is a pretty big place and, after all, we've never been farther from
earth than our moon. How do we know what the stars are made of?
This is the electromagnetic spectrum. It consists of waves which vary in
length from very long (radio waves) to incredibly short (gamma rays). A
special part of the spectrum consists of waves that we can see. This is
called the visible spectrum. We see different wavelengths as different
colors ranging from red (long wavelengths) to blue/violet (short wavelengths).
White light consists of all visible wavelengths together. When white
light passes through a prism, a triangular piece of glass or plastic, the
different wavelengths are separated and can be seen individually.
This instrument is a spectroscope. This one is attached to a telescope
to separate the light from stars into a spectrum of different wavelengths. Scientists can then look for specific patterns of wavelengths.
When any element is heated hot enough it begins to emit light.
The pattern of wavelengths emitted by an element are like a
fingerprint. Each element emits its own unique pattern.
Above you can see the pattern of wavelengths emitted by the
element hydrogen. Whenever this pattern is seen in the light
coming from a star it means that hydrogen is present on that
star.
This is called the emission spectrum of hydrogen.
This is the pattern of wavelengths emitted by iron. When
iron is heated until it vaporizes, as in a star, it emits this
unique pattern of wavelengths. This is the emission spectrum
of iron.
Below is the emission spectrum of nitrogen. If scientists see
this pattern in the light from a star they know that nitrogen is
present.
So by using a spectroscope scientists can analyze all the wavelengths
that are emitted by a star and can tell exactly what the star is made
of even though it may be thousands of light years away.
calcium
uranium
oxygen
What else can the light from distant stars and galaxies tell us?
When an object such as a star or galaxy is moving towards us the
the wavelengths of the light it emits are shifted towards the blue end
of the spectrum (frequency is shifted higher). This is called blue shift.
If the object is moving away its light is shifted towards the red end of
the spectrum (frequency is shifted lower) . This is called red shift. This
phenomenon, the shifting of wavelengths due to the relative motion of
objects, is called the Doppler Effect.
You have experienced the Doppler Effect every time you listen to
a car drive by. As the car is approaching the pitch is shifted higher and as it
passes and moves away the pitch (frequency) is shifted lower (click).
Click car to hear sound again
Doppler Effect
• Shifting of wavelengths can occur with both
sound and light
• Doppler effect is easier to observe with sound
– With sound you will hear a change in pitch
– Imagine an ambulance approaching a person standing
on a sidewalk:
• As the ambulance moves closer the pitch becomes higher
• As the ambulance moves away the pitch becomes lower
Ambulance Doppler
Train Doppler
The Doppler Effect is used...............
> to tell us the speed of a fastball.
> to help police to catch people traveling over the speed limit.
> permit meteorologists to identify and track storms such as tornados.
> analyze the flow of blood through arteries.
To sum up...... If frequency is shifted lower (red shift) it means
the object is moving away,
If frequency is shifted higher (blue shift) it means
something is moving closer,
and the amount of shift indicates the speed that object
is traveling.
How is the Doppler effect used in astronomy?
This is the pattern of wavelengths emitted by the element helium.
This is the pattern of wavelengths of helium that is found in the
light from distant stars and galaxies. We know it's helium because
the pattern is the same but notice that all the wavelengths are
shifted towards the red end of the spectrum.
What does this mean?
First, it means that there is helium on that star and...................
second, it means that the star is moving away from us. Red shift!
Remember, the greater the amount of shift,
the faster the star is moving!
Helium
Helium slightly red shifted. Moving away.
Helium more red shifted. Moving away even faster!
Blue
Red
Red Shift – object is moving away
Blue
Red
Blue
Red
Blue shift – object is moving closer
Blue
Red
Blue
Red
No shift – object is moving same speed
Blue
Red
ALL of the light from stars and galaxies that reaches the earth
is red shifted. What does that mean?
It means that everything is moving away from us!
How can everything be moving away from us?
The only explanation for that is .............................................
THE UNIVERSE IS EXPANDING!
And if the universe is expanding then long ago it must have
been much smaller. The expansion began about 12 billion
years ago with the.................
BIG BANG!
To understand the Big Bang
just imagine that the galaxies
are located on the surface of
an inflating balloon.
As the balloon expands, every
point on its surface is moving
away from every other point.
So what can we learn from the light from stars?
We can find out what stars are made of by examining the spectra.
We can tell that they are moving away from us and that...............
The universe is expanding.
We can calculate the speed of that expansion and........................
And we can infer the age of the universe (12 billion years).
All this just from starlight!
Red Shift/Blue Shift
• when a light emitting object moves away
from earth the waves get longer… Red
Shifted
• When it moves towards earth they get
shorter… Blue shifted
Red Shift/Blue Shift
» Red Shift
» Blue Shift
Atoms and Light
• The movement of electrons inside of
atoms produces light and other
electromagnetic radiation.
• Sunlight produces every color in the
rainbow but…
• Each element gives off only certain
frequencies of light, called spectral lines.
In effect each element has its own
signature of spectral lines allowing us to
identify which element we have or what
stars are made of.
Below is a picture of the spectral lines
given off by hydrogen. Note there are 3
different frequencies.
• The emission spectra makes it
possible to identify inaccessible
substances. Most of our knowledge of
the universe comes from studying the
emission spectra of stars.
• Below is the spectra of a few more
elements.
Helium
• Neon
• Argon
• In a star, there are many elements
present. The way we can tell which are
there is to look at the spectrum of the
star.
• From spectral lines astronomers can
determine not only the element, but the
temperature and density of that element
in the star
• Emission lines can also tell us about the
magnetic field of the star. The width of
the line can tell us how fast the material
is moving
• If the lines shift back and forth, it
means that the star may be orbiting
another star - the spectrum will give
the information to estimate the mass
and size of the star system and the
companion star.
• Around a compact object (black hole,
neutron star), the material is heated to the
point it gives off X-rays, and the material
falls onto the black hole or neutron star. By
looking at the spectrum of X-rays being
emitted by that object and its surrounding
disk, we can learn about these objects.
Classwork
• Read p. 370-373
– Answer page 373 #1-3, 5, 7-9
• Read p. 375-382
– Answer page 382 #3-4, 6, 7, 9
Retrograde Motion
You’re going the wrong way!
History of Retrograde Motion
• Ancient Greeks noticed that certain
celestial objects changed their locations
from time to time
• They called them “wanderers”; ‘planet’
comes from that Greek word
• Greeks charted stars and planets, noticed
that planets seemed to stop and change
direction sometimes
RETROGRADE MOTION
Due to differences the rate that they
revolve around the sun.
Some planet seem to change the direction
of their orbit (go backwards).
Mars & Jupiter revolve more slowly around
the sun than the Earth
To us they seem to go backward
sometimes.
retrograde motion Jupiter:
• http://www.youtube.com/watch?v=Wl5deoW5xkI&fe
ature=related
Time lapse of Mars
Retrograde Motion
• For superior planets (further from the Sun
than Earth)
• Earth orbit is faster than these planets
• Earth catches up to a planet in its orbit
• Planet appears to stop and move
backwards (West to East)
• YouTube “Retrograde Motion and the
Opposition of Mars”
http://www.youtube.com/watch?v=72FrZz_zJFU
The Ecliptic Line
The Ecliptic
• Apparent path of the Sun and planets through
the night sky
The Ecliptic
• Q: How far (in degrees) would the Sun
move along the Ecliptic each day over the
course of 1 year?
• Hint: There are 360º in a circle and 365
days in a year
• A: about 1 degree (width of your baby
finger at arm’s length)
Galaxies and their shapes
SNC1D
What is a galaxy?
A galaxy is a huge collection of stars, gas
and dust measuring MANY light years
across.
This is the Milky Way
Galaxy where our Solar
System lives:
Regions of the Milky Way Galaxy
diameter of disk = 100,000 l.y. (30,000 pc)
thickness of disk = 1,000 l.y. (300 pc)
number of stars = 200 billion
Sun is in disk,
28,000 l.y. out
from center
play brf
Regions of the Milky Way Galaxy
• Disk
• younger generation of stars
• contains gas and dust (Nebulae)
• location of the open clusters
(An open cluster is a group of up to a few thousand
stars that were formed from the same giant
molecular cloud )
• Bulge
• mixture of both young and old stars
• Halo
• older generation of stars
• contains no gas or dust
• location of the globular clusters (A collection of
hundreds of thousands of old stars held together
by gravity )
Classification of Galaxies
• Using a system invented by Edwin Hubble,
astronomers classify galaxies into three major
types:
• Spiral
• Elliptical
• Irregular
• The sizes of all three types span a wide range:
• dwarf galaxies
• which contain 100 million (108) stars
• giant galaxies
• which contain 1 trillion (1012) stars
Spiral Galaxies
• have a disk component and bulge & halo
• disk contains Interstellar medium (ISM) of gas & dust
• relative sizes of bulge/disk & amount of ISM vary among
galaxies
• appear white because they contain both blue (HOT) & red
(COOLER) stars
Elliptical Galaxies
• only have a bulge and halo; NO disk component
• very little ISM, which is mostly low-density and
ionized
• appear red because they contain mostly red stars
(cooler stars)
Irregular Galaxies
• “none of the above”
category; neither spiral nor
elliptical
• appear white & dusty with
ISM
• have more in common with the
disk component of spirals
• distant galaxies are more
likely to be irregular
• they were more common when
the Universe was young
Homework
• Find an Astronomy Picture of the day of a
galaxy. Print the picture and an provide
explanation (IN YOUR OWN WORDS) of
the picture. State the name of the galaxy,
shape and some characteristics of that
galaxy.
http://antwrp.gsfc.nasa.gov/apod/archivepix.html
Astronomy Picture of the Day
• Explanation: NASA's COBE satellite scanned the heavens at
infrared wavelengths in 1990 and produced this premier view of the
central region of our own Milky Way Galaxy. The Milky Way is a
typical spiral galaxy with a central bulge and extended disk of stars.
However, gas and dust within the disk obscure visible wavelengths
of light effectively preventing clear observations of the center.
In the core of stars fusion occurs (according to E=mc2)
causing the star to give off radiation.
“Nebulae”
Vast Clouds of dust
where gravity starts
to pull “inter-stellar”
material together
Main Sequence
Accumulating gas causes the
internal temperature to rise (10
000 000oC) and fusion begins.
Main Sequence - helium accumulates in the core of the star as it continues to
heat up. The increased outward pressure (due to heat) is balanced by the
suns’ gravitational force making it stable.
All main sequence stars follow the common life Dust
Star
Giant
At the line they may follow separate fates...
Are not main sequence stars...
Low mass stars consume their hydrogen very slowly (100 Billion years).
Eventually they lose all their mass and become a very hot white dwarf.
Consume their hydrogen a little faster over 10 billion years...
Once the hydrogen has been used up, the outward pressure is less than
the gravity so the star collapses.
Antares
Betelgeuse
Massive heat is then generated
that starts to fuse the core to
Carbon while the gases slowly
expand away (Red Giant)
Stellar winds will pull the expanding
gas away leaving a “Planetary
Nebulae” and the hot inner region of
the star (White Dwarf)
The white dwarf ultimately fuses to a solid carbon “black dwarf”
A 25 solar mass star will only last 7 Million years (it burns quickly)
As it rapidly burns out, the core will become so hot it will fuse into iron. Now
fusion has stopped nothing will counteract the force of gravity. The star collapses
and releases a huge shockwave outwards (supernova).
The remaining core is so dense it
either becomes crushed into a super
dense 10-20 km neutron star (mass
~1.5 - 3 Solar masses)
Or...
http://www.uncg.edu/~aavolkov/bh/index.htm
For stars that are 3x the size of our sun the gravity is so great that they collapse
into “singularity” - that is the pull of gravity is so great it “crushes” the neutron star.
Diameter = 12750 km
Earth before collapse
(NOT to scale)
Diameter 1.66 cm
The REAL size
of the Earth if it becomes a black hole
(Imagine yourself a living on SUCH a planet)
Essentially it is enormous Gravity and Mass isolated to a tiny spot of space.
Galaxies, Supernovas, &
Black Holes
SNC1D
General Galaxy Information
Galaxies are vast systems of stars that populate
the Universe.
Typically contain several million to some trillion
stars.
They also contain various types of star clusters
and nebulae.
star cluster=Globular clusters are gravitationally
bound concentrations of approximately ten thousand
to one million stars.3
nebulae= clouds of dust or gas
General Galaxy Information
Our own Milky Way galaxy is just one of
the billions of galaxies now known to exist.
A typical galaxy is 100,000 light-years in
diameter.
The nearest giant neighbor is the
Andromeda Galaxy, a spiral galaxy, and is
about 2-3 million light years distant.
Types of Galaxies
Spiral ~75%
Elliptical 20%
Lenticular
Irregular 5%
Types of Galaxies
Types of Galaxies
Some elliptical galaxies show no evidence of
having formed stars since a brilliant epoch early
in cosmic history, while spiral and irregular
galaxies have been making stars briskly over
their entire lifetimes.
Some galaxies produce most of their energy
deep in the infrared, and some are so diffuse
and faint as to be barely detectable against the
faint glow of the Earth's night sky.
Hubble Approaches 'Final Frontier'
Several expert teams have at last identified what may
turn out to be some of the earliest star-forming
galaxies. These faint sources, circled in the image
above, illustrate how astronomers can begin to explore
when the first galaxies formed and what their
properties might be.2
A Galactic 'Late Bloomer'
NASA's Hubble Space Telescope has snapped a view of
what may be the youngest galaxy ever seen.
Spitzer's Legacy
NASA's Spitzer Space
Telescope has
captured infrared
images of the
"Whirlpool Galaxy"
(M51), revealing
strange structures
bridging the gaps
between the dust-rich
spiral arms, and
tracing the dust, gas
and stellar populations
in both the bright spiral
galaxy and its
companion.
The Milky Way Galaxy
We are part of the Milky Way Galaxy.
Diffuse band of light crossing the night sky.
A flattened disk of stars with a central bulge.
Our own galaxy can be traced at least fifty thousand lightyears from its nucleus, and we know of many galaxies much
larger yet.
1610: Galileo first observed the Milky Way with his new
telescope.
The Milky Way Galaxy
1901 thru 1922: Jacobus Kapteyn
Used photographic star counts
Estimated distances statistically based on
parallaxes & proper motions of nearby stars.
Neglected interstellar absorption of starlight.
Flattened disk 15 kpc across & 3 kpc thick
with the Sun slightly
off center.
The Milky Way Galaxy
The Problem of Absorption!
Absorption of Starlight by Interstellar Dust:
Interstellar space is filled with gas and dust
Dust absorbs/scatters light, making distant objects
look fainter.
If left unaccounted for, it leads to overestimates of
Luminosity distances.
Plagues all attempts to map the Milky Way
The Milky Way Galaxy
Present Picture
Largely Shapley's model, corrected for the effects
of interstellar absorption.
• A flattened disk of stars with a central bulge.
• ~25 kpc in diameter and ~1 kpc thick
• Sun is ~8 kpc from the center in Sagittarius
• Galactic Center and much of the disk is
obscured by dust in the plane of the Galaxy
The Milky Way Galaxy
Black Holes
A region of space-time from which nothing can
escape, even light.
It is impossible to see a black hole directly
because no light can escape from them; they are
black.
If a neutron star is too large, the gravitational
forces overwhelm the pressure gradients and a
collapse cannot be halted. The neutron star
continues to shrink until it finally becomes a
black hole.
Black Holes
Two Types Of Black Holes
Non-rotating, spherically symmetric black
hole, first postulated by Schwarzschild.
A rotating, spherical black hole, predicted in
1964 by the New Zealand mathematician Roy
Kerr.
Schwarzschild Black Hole
If you envision the simplest three-dimensional
geometry for a black hole, that is a sphere (known as
a Schwarzschild black hole), the black hole's surface
is known as the event horizon.
Black Holes
Black Holes
As we round the giant hot blue star, we see its tiny
companion, a black hole whose gravity is so intense that
it is stripping the outer layers of gas from the star.2
Supernovas
When a large star has burnt all its fuel it
explodes into a supernova.
The leftover material collapses down to an
extremely dense object known as a neutron star.
A supernova occurs in our galaxy once every
300 years, and in neighboring galaxies about
500 neutron stars have been identified.
Supernovas
A recent event of this kind was observed in 1987
when a star weighing the equivalent of 20 suns
blew up in a neighboring galaxy 160,000 light
years away.
If after such an explosion, the remaining material is
greater than 1.4 solar masses, it will contract into an
unimaginably dense core made solely of neutrons.
Neutron stars are so dense a teaspoonful would
weigh 100 million tons!
If the star's final mass exceeds much beyond 2 solar
masses, there is no outward force that can resist
gravity. The core continues to collapse to a critical
size or circumference beyond which there is only one
fate: to form a black hole.
Supernova
Supernova Remnant Turns 400
This combined image -- from NASA's Spitzer Space
Telescope, Hubble Space Telescope, and e Chandra Xray Observatory -- unveils a bubble-shaped shroud of
gas and dust that is 14 light-years wide and is expanding
at 4 million miles per hour (2,000 kilometers per second).
Question 1
A galaxy is comprised of:
a) several million to some trillion stars.
b) several hundred stars.
c) several thousand stars.
d) several stars.
A
Question 2
We are part of the:
a) Andromeda Galaxy.
b) Papillon Galaxy.
c) Milky Way Galaxy.
d) Sombrero Galaxy.
C
Question 3
The most common type of galaxy is a/an:
a) irregular galaxy.
b) lenticular.
c) elliptical.
d) spiral.
D
Question 4
A black hole is:
a) impossible to see
directly.
b) a region of spacetime from which
nothing can escape,
even light.
c) a shrunken neutron
star.
d) all of the above.
D
Question 5
The collapsed material from a supernova is
known as:
a) a neutron star.
b) a black hole.
c) a planet.
d) useless crap.
A
Question 6
When a large star has burnt all its fuel it
explodes into a:
a) neutron star.
b) black hole.
c) supernova.
d) galaxy.
C
Question 7
A supernova occurs about once every:
a) 3 million years.
b) 3,000 years.
c) 300 years.
d) 30 years.
C
Question 8
Did you like my cool pictures?
a) Yes!
b) Yes!
c) Yes!
d) All of the above.
D
Interesting Links
1- Introduction to Stars, Galaxies, & the
Universe by Prof. Richard Pogge
http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit4/
2http://www.nasa.gov/multimedia/imagegallery/archives1.ht
ml
3- Galaxies
http://www.seds.org/messier/galaxy.html
4- Types of Nebulae
http://nineplanets.org/twn/types.html
Interesting Links
5- Introduction to Black Holes
http://www.damtp.cam.ac.uk/user/gr/public/bh_intro.html
6- Galaxies
http://www.astr.ua.edu/goodies/data_resources/galaxies.text8
7- A Black Hole is Born
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/BlackHoleFormation.html
8- The Hubble Tuning Fork
http://cas.sdss.org/dr3/en/proj/advanced/galaxies/tuningfork.asp