cc
to Wednesday Nite at the Lab. I'm Tina Hauser and I produce
Wisconsin Public Television's University Place.
On behalf of Wisconsin Public Television and our partners,
the Biotechnology Center, the Science Alliance,
the Wisconsin Alumni Association
coming to Wednesday Nite at the and UW-ExtensiLab.thank you for
We do this every Wednesday
Tonight, it's my pleasure nito introduce to your.
Dr. Sanjay Limaye.
NASA's Venus Exploration Dr. Limaye is the chair of
His research interest is in the atmospheric circulation on
planets and he began his career with research on the circulation
of the Venus atmosphere from
He joined the Space Science and Engineering Center at the
University of Wisconsin-Madison in 1980 to continue research on
planetary atmospheres.
with the European Space Agency's He is a participating scientist
involved in coordinating the Venus Express mission and is
Dr. Limaye's topic tonight is cothe 2012 transit of Venus..
A truly extraordinary event, as humanity will not see another
transit of Venus for more than a
Please join me in welcoming Sanjay Limaye to Wednesday Nite
at the Lab. [applause]
Tina, it's a pleasure to be here to give this talk.
Some of you heard a little music
You may have thought it was the 4th of July, since the weather
has been so warm in Madison.
Well, lilacs are blooming, [laugher]
the birds are singing. the tulips are out,
but it's not. I played that march because, all
of you recognize it I'm sure, John Philip Sousa.
He composed a march to
Venus. commemorate the transit of
Now, I wasn't around for the That's the Venus March.
one century ago, last transit, obviously,
But what is it about Venus in Madison.
start explorations to go around trthe world, force England ando
France to ignore the Seven Year War and collaborate and observe
Venus?
march. That led Sousa to compose a
went and composed another one, Not only that, but he actually
There's actually another novel the Transit of Venus.
this century that documents the abtrials and jubilations of ain
French astronomer, Gentil, who
observe the transit. had gone to India in 1761 to
about the transit that makes it The quso interesting? is it
That we have so much excitement?
out, yes. So a little bit about Venus, I
think it's too bad it's a little
but hopefully by the time I finish this talk the skies might
be clear. You can go out and you can
probably see something like this.
This is a picture taken from
You see the moon in the lower Madison jleft corner.eks ago.
Then you see Jupiter, and up
Venus, as you know, high, has been seen both--enus.
It has been seen in the morning sky, in the evening sky, because
it is an inner planet.
sky, and people have claimed It's the brightest object in the
by Venus on a moonless night. I actually met a person who had
seen his own shadow.
some of you have. IIf not, if you are in a dark
spot, you can try.
one of the five vindras and it Venus was known to ancients as
him in almost all the calendars obviouslthat we know of.d after
I mention only Hindu here because I think, as far as I can
find out, the observation of
to several millennia before Venus and the2000.ets goes back
It goes back at least two of
So it has a day named after Venus in the calendar, Shurka.
Shurkawar, today is named after Mercury, as all of you know.
If you wonder way astronomy and the calendar are co-related,
it's essentially because it's how we keep time.
Times of the day, days of the week, the year, came from that.
The Mayans also of course had been observing Venus.
There are better experts than me
experience. But in the modern era, at least
since "the Copernican Revolution," when the
heliocentric theory was being proposed and excepted, Venus has
been excepted, and why? Before we get into that,
why explore Venus?
neighbor. It's the planet with the
largest, the most significant greenhouse effect that we know
of. What can we learn by finding out
about Venus?
in the last fifty years-- I should point out that this is
the 50th anniversary of the beginning of the space
exploration, or planet
Mariner 2 was launched in 2012, July, and got to Venus in
December. So they're marking that
anniversary.
Venus? What can we learn by observing
and on the right side is a Here's a picture of Mariner 2,
craft, which didn't make it. picture of the Soviet space
[inaudible] Isn't it on?
[inaudible] Well, I don't know how this
audio system works. Is there somebody there
who can help me?
I don't see a microphone here.
All right. [inaudible]
Okay, we'll try it. >We'll find out.h?
Thank you.
and in the lower right is one of In the upper left is Mariner 2
Venera 2. Actually, it reached Venus but
it didn't quite survive.
this is 2006, a picture of Venus Then we jump to the recent days,
launched by the European Space taken from a current spacecraft
And on the left it looks like a round planet with a dark part in
the middle. That's because it's a single
shot of Venus, it's a single
On the left side you see Venus picture.
the right side is the night side in reflected daylight, and on
heat emitted by Venus. of Venus and we're seeing the
Venus is so hot at the surface, Tha473 degrees Centigrade, orot.
roughly 950 Fahrenheit, that it emits enough light that heat
leaks through the clouds of Venus and we can detect it.
The question is, are we likely
Because we have learned in the to go down that path?
have liquid water at some point last 50in it's history.us did
To go back to the topic that
today and explain what I've learned, I just want to give you
an idea of how much the ancients
Here's a table knew about the planetary orbits.
and I was surprised. that I just created today,
sun, moon-- Oops, I've got one extra O there
in the "moon."
Mercury, Venus-- [laughter]
Well, it's Wisconsin after all! Venus, Mars Jupiter and Saturn.
The next column gives you the number of revolutions in a
Mahayuga. A Mahayuga is a way of measuring
time in the Puranic system, and it corresponds to that number,
1,577,917,828 days. So it's a real long period.
How did they determined that
something interesting. many number of revolutions is
English translations of Surya Siddhanta and find a description
of that in that.
days, that's the third column Bfrom the left, and you see thee
amount of time Earth takes to go
value is in the next column. around the sun, and the current
values are extremely accurate. You can see that all of these
the advent of the telescope and before we had modern
instruments,
Despite all these measurements, what they were able to figure
out was the distance of the moon
diameter. aYou might wonder how, but's
I think if you think about it,
if you find out when eclipses it sort of occur.s obvious,
The Indian astronomers had
predicting when the lunar eclipses and the solar eclipses
were going to occur.
determine that, for both the sun From that they were able to
108 times the diameter. aThe modern values are 110.4as
and 107.5.
or 3,000 years back. This is going back 2,000,
how large are the sun and the The question moon?ned, however,
Unless you know their actual
absolute measure of the sizes you distance.ally get an
That where, basically, the
That problem remained until the 17th century..
By that time they also had a
Earth. good measure of the size of the
which is a unit they had used. This is given in terms of --,
or about 6-1/2 miles. These are the values that they
had determined. The ratio is about .9 so they
had estimated them to be about
But nevertheless, remarkable. Now you fast forward to the
17th century, because the distance to the sun still wasn't
known.
learned or know already that, BCopernicus had been proposinge
the heliocentric theory.
planetary positions from Europe. Tycho Brahe was measuring the
laws of planetary motion, which Ais significant, because hee
showed that the planets moved in
observations could be used to predict the future positions of
the planets if you had prior
were. Sir Isaac Newton came along and
he was able to tie it together
Using Kepler's laws, he could ftell the relative distances of.
the planets which were known to the Hindu astronomers many, many
centuries earlier, but not in the West.
But nobody could know the distance between the Earth and
the sun.
proposed the theory of planetary So here's Copernicus and he had
Tycho Brahe, in the 16th century motion.
observatory. who had established an
the use of the telescope. The telescope had not invented
yet until Galileo came along. Actually, Galileo didn't invent
it, but he used it. Then Kepler, from 1571 to 1630,
had formulated the equation from
planet's position in the future. which he could predict the
had to have accurate knowledge The trouble is that you still
to do that he worked with Tycho Brahe to create what are called
the Rudolphine Tables.
Because they were named after King Rudolf, I believe, in
Denmark.
was supporting these Emperor Rudolf was the one who
These tables were crucial in the calculations.
Kepler was able to predict that by 1631 there would be transit
of Mercury and people did actually observe it.
He had missed the transit of
a British astronomer, barely 24 years of age, was looking at the
table and he realized some
At this point I just want to problems with these tables.
astronomy and the planetary ppositions are significant.e
Essentially, they led to the
in the 18th century. discovery of Uranus and Neptune
Because as we started to track How?
People could find out that they were not entirely predictable
using Kepler's laws.
in the positions. ThereUranus and Neptune aretions
significant because their presence was predicted because
people surmised that there had
beyond the orbit of Saturn. People looked for it and, first
Uranus was found and later, Neptune was found.
Until that time, or a few years after that, people kept making
planetary position measurements.
of planets still didn't Errorcompletely go away.itions
So another planet was a possibility, and that led to the
discover by Clyde Tombaugh in 1930, of Pluto.
That continued. People thought there had to be
another planet beyond Pluto,
also not be predicted very because Pluto's positions could
something called Planet X in the accurately, and that led to
heard. '70s, as some of you may have
the space era began, and we had good measurements of the masses
of the planets and better observations of the planetary
positions.
observed for a much longer Because Uranus, Neptune had been
better orbit solution for them. The need for Planet X went away,
and it turned out Pluto was also
demote it. very small, so that to the IU to
it's still a planet. Now it's a dwarf planet, but
A transit is simply, think of it What is a transit?
too small. as an eclipse but the object is
a planet is too small because of It cannot cover the sun, because
It happens when the orbit of the distance as seen from Earth.
location, is such that Venus Venus, with respect to its
That's really what a transit is. goes in front of the sun.
this diagram is, the inclined eclipse that you see, is the
orbit of Venus
and that inclination was known which is at about 3.4 degrees,
The dark, shaded eclipse that foryou see is Earth's orbit.es.
This is the perspective view. When Earth and Venus are lined
up so that Venus is directly in front of the sun, that's
essentially a transit.
kind of a resonance between the Norbital periods of Venus ands
Earth.
from the table earlier, Venus Thtakes about 225 days to gow
around the sun. That means, that in roughly
eight Earth years, Venus has
sun. completed 13 orbits around the
to a long period between when IVenus and Earth are alignedds
directly in front of the sun, given the inclination.
Here's an example of that.
myself here. I'm getting slightly ahead of
concept of solar parallax. I wanted to introduce the
is angle if seen, say, from the Bnorth pole of Earth and theun
south pole of Earth.
what I mean by paralax. If not, hold out your index
finger, and if you close one eye
that finger, then switch the and try to find something behind
object has moved. eyThat's basically parallax.he
That happens if you are looking at an object that's very close
to you, and if you change your
appear to have moved even though position, that object will
That's the idea behind parallax. it has not moved at all.
if you observe the apparent Ifposition of the sun from the,
north pole and the south pole,
It's that angle that angle that people are trying to measure
looking at transit of Venus.
Well, the inclination is about Why are those always rare?
because of the orbital periods 3.4 degrees and, essentially,
roughly 105 and 120 years before of Earth and Venus, it takes
Eight years is just when Venus they are lined up again.
from Earth. Going back to Galileo.
This is early 17th century. Telescope hadn't been invented.
It was used in Holland. Essentially ships were using it
to scope out territory, such as it was.
Essentially, used as a spying tool.
Galileo obtained a copy of it and here's, I don't know if
you can see it in the picture,
picture of Galileo's telescope but in the lower left is a
In the middle you see a drawing of Earth and a schematic view of
where Venus would be. You can see what Venus would
appear like.
of what the drawings that he This is essentially a sketch
On the lower left-- I don't know how the mouse
works here. Let's see, does this--
I don't see a mouse.
animation of Venus going around the sun and in the left you'll
see what the illuminated portion
On the bottom left, you'll see of Venus would look like.
Venus at the bottom. the drawings of the phases of
planets. At the top are the other
size of Venus changes over a few Galileo noted that the apparent
If you're able to see Venus motonight through binoculars I.
would highly recommend that you go out and see it.
You'll be surprised that, even
you'd think you would see a though Venround disk.ry bright,
You won't.
crescent. WhNo, not a crescent. a
It's almost at the position, so you'll see roughly a 90 degree
slice.
half-disk. Roughly a gibbous, or a
significant, because that was Thone of the key pieces ofs
evidence of the theory that planets go around the sun and
not around the Earth. If Venus went around the Earth
you wouldn't get a change in
That was a key point. Here's a picture of, these are
real images taken by armature astronomers in 2004 and they
basically show you what the apparent size and shape would
look like.
The last one is significant, They are to scale.
That's when Venus is directly in because it shows a ring.
the sun, slightly over or above. front of the sun, but not over
of Venus. ThThat discovery was made by ae
Russian astronomer, a scientist,
That's the first planetary Mikhail Lomonosov in 1761.
That's the first time we learned discovery ever made.
That Venus had an atmosphere. Until that time we knew nothing
about any planet. That was roughly 250 years ago.
Last year was the anniversary of that discovery.
Going back to the Rudolphine
Tycho Brahe had created. Tables that Kepler and
and Venus would pass in front of They predicted that both Mercury
accuracy was not high enough. One person, Pierre Gassendi, in
Paris, actually tried to observe
the time was off by a few hours. a transit of Venus in 1631, but
didn't see it. It occurred at night, and he
transit. Kepler had missed the next
Or at least he didn't think that there would be a transit in
1639. This is when a young Jeremiah
Horrocks, who had attended
not graduate. At least there is no record of
his graduating. He was near Liverpool.
He was teaching,
contact with another astronomer in Manchester named William
Crabtree who was a cloth
They had corresponded and exchanged information about the
Rudolphine Tables, and they were
finding that there were some observing Venus regularly, and
Interestingly, if you read his errors in the tables.
was re-printed some time back. biography which was in print, it
about a Belgian astronomer, He makes Lansberg.y comments
Lansberg had also continued the effort of creating these
observations. Unfortunately, they were
more in error than Kepler.
talks about Lansberg in somewhat So in his biography, he actually
So they were able to use these unfavorable terms.
refinements. observations and their own
event in November, they knew About a month before the actual
happen. tThey were the only ones to
actually see that transit.
He had seen the Mercury transit I mein the 1631 transit.di.
Then we come to Jeremiah Horrocks.
This is a painting by Eyre Crow,
Horrocks had actually observed painted many, many years after
To observe the transit, he it.
the image of the sun through a darkened his room and projected
He observed it on the wall. There's some interesting stories
about how he had to leave the room, because he had to go to
church and give a sermon. [inaudible]
The transit is simply-- Have you seen an eclipse?
Like the moon goes in front of
Venus is going in front of the the sun?
spot in front of the sun. That's just what a transit is.
So what he was observing, and they had a nicely raticulated
piece of paper so they could
observe exactly where Venus was takon the surface of the sun.uld
That's a drawing of how they
Now, whether Horrocks actually observed it.
guess. looked like that is anybody's
William Crabtree observing There's another drawing of
He also observed the transit in the same way, projecting it from
a telescope onto a piece of paper in his room.
And presumably, that's his
That painting is in the Manchester City Hall.
It was painted by a very famous English painter, Ford Maddox
Brown, who lived 1821-1893. It was one of the few.
I think he painted like 12
Manchester, and this is one of paintings for the city of
Maybe some of you have seen it. I have not seen it myself, even
though I've been to Manchester. Now, the 1639 transit was seen
by just those many people.
Crabtree, and their family. There's no record of anyone else
observing that transit. Luckily, the did make good
drawings and records. On the right is an actual
drawing, or a copy of it, from
times, the duration, and the Jeremiah Horrocks, with the
and the Sun, as percent of the distance of the centers of Venus
They were able to deduce the Sun's diameter.
let to a slightly smaller value parof the Astronomical Unit,that
although that was not his aim.
simply trying to observe the I think at that point, he was
Venus. transit and the position of
reported, Sir Halley took note So, after that transit was
who had also predicted that the of transits could be used toson
measure the distance to the Sun,
by measuring parallax. basically the Astronomical Unit,
is you observe the transit from different points on Earth, and
the apparent difference between the path of Venus across the Sun
as seen from those two points,
estimate the can give you the geometry to
This was so significant, because mean distance to the Sun.
Harrison had already developed at that time, I remember
I think some of you may have a good nautical clock.
by Dava Sobel, who had given read the book "Longitude"
So to really use these transits, a talk here some years back.
really need to know the time to understand them, you
So if you're going to send really well.
a way of keeping good time. So these clocks, the development
of the clock was very significant.
King George III was so impressed
observatory at Kew, specifically for that purpose.
Okay, so the 1761 transit led to
Lomonosov, as I pointed out a discoearlier.Mikhail
He discoverd the atmosphere of
He also noticed something that Venus.
exactly when Venus was touching, he found it difficult to tell
edge of the Sun. or came into contact with the
become more important later on. That's the Black Drop Effect.
To give you an idea of what the Black Drop Effect is, if you
bring your thumb and index
simply hold it in front of a finger, and without touching,
appear to touch each other light, you can see that they
touch. before they actually physically
when Venus moves in front of the This is something that happens
This effect essentially was the main problem.
So King George had sent off James Cook to observe the
transit, which could only be
So he went straight down and seen from the Pacific.
of South America, and then went sailed arounwest. southern tip
That's his statue in Tahiti, in the area where he parked his
ships.
Tahiti. He and his captain drew drawings
of Venus. They differed in their estimates
of exactly when Venus came into contact with Sun because of this
Black Drop Effect.
but they could not agree on the Sprecise time, and it actually,
led to some action against a his
They had to be separated. But that transit of 1769, also
later on, created a lot of stir in the public.
Here's a drawing. I have no idea what that
character in the garden is doing
But it led obviously, to several postage stamps.
Here's a drawing of how Captain Cook observed it.
He himself did observe it, and
It's pretty fun. then the drawings.
methods to measure the distance, So, there are actually four
what an astromical unit is. One is simply by looking at the
transit of Venus across the face
locations on Earth, using the separation of the parallax.
Another is measuring the rate at
the Sun. which Venus crosses the disc of
times. So for this, you need accurate
actually four separate times As you can see, there are
leading edge of Venus first touches the sun; when the
trailing edge touches the disc
and the same thing when it's of the Sun for the first time;
So there are four separate exiting the disc of Venus.
You can go through a lot of complicated geometry and
calculus and try to figure out
I'm not going to through that, the parallax.
the 1761 and 1769 transits but the result of estimates of
I mean, the estimate was like 109 million miles from the 1761
transit.
million, so it was way off. Measurements in 1769 led to a
much lower value, 88 million, which is somewhat closer to the
actual value of 93 million. The main problem was the Black
Drop Effect.
eyes were not really suited for Peopmaking that observation.eir
So now we turn to the next
By that time, photography had been invented.
The next transits were in 1874
People thought, gee, if they and 1882.
the Black Drop Effect. took a picture, you wouldn't see
US Naval Observatory. If you go onto the Internet, you
can probably see an animation of
You can see Venus going across several of these photographs.
Many years later, after these observations were made, they
came up with an estimate of what
If you go to 1862-1874, the line, you can see that the
different estimates are about 91.7, 92.7, and if you take
all the previous transits and allow for errors, they came
up with 92.797 million, which is close to the modern value.
So the effort to measure the
succeed by 1882, but it took Astronomical Unit did indeed
150 years, to actually get to a long tithat value.more than
By that time, people had
smaller asteroids that had been discovered, Eros, they could be
used because they're smaller, and they wouldn't create so much
of a Black Drop Effect. So Eros actually gave a very
good value of 91.5. If you take all of these
measurements, they still arrive at about 92.67 million miles.
That's where things stood until 1961, when something spectacular
happened. As you recall, during the World
War, to protect enemy planes, the radar was being worked on at
MIT in Lincoln Labs.
working on radar. They decided to find out what
would happen if they turned the radar toward Venus.
So in 1961, they obtained the first echo from a planet, a
celestial object, by sending
Now, back in those days, I think radar beams to Venus.
distance to Venus was at that Ipoint, but it was around
4.5 or 5 minutes, I believe.
When they tried it again, They did they failed.ho back.
At the same time, there was s student, Goldstein, who was
working at Cal Tech.
radar. They were also developing the
he could use Venus as a target So he talked to his advisor, if
Basically, he was told, go for the radar.
[laughter] ahead, but no echo, no thesis.
the echo back, and they were Fortunately for him, he did get
There was a difference in the able radars.at it.
The MIT radar was a pulse radar,
bursts, and they had to wait for which sent a series of short
the GTS was a dual system. the echo back, whereas
telescopes. They broadcast a tone from one
dish continuously, and then looked for the echo from the
other dish. They worked differently, but
they were able to get the delay,
waves from Earth to Venus and the transit back.of the radio
At exactly the expected time, they received the signal, and it
disappeared when they stopped the transmissions.
So that led to the currently
Astronomical Unit which is accepted value of the
So, if we have determined 9the Astronomical Unit,.
why do we care about the Venus
That's the question. transits?
happened, is we launched the Well, since 1960, what has
Now we can observe the transits lunfrom space.ft.
This is a view of the transit of
American satellites. Mercury from TRACE, one of the
that's an actual image of Mercury against the disk of the,
Sun.
it's not taken in white light, The Sun looks modeled, because
wavelength. I forget the exact wavelength,
but I believe it's--
going on, the connective So it's showing you the activity
surface of the Sun. But notice that it's not a
straight line.
that. MercuSo what's going on?g like
This is actually an illustration
Remember, this is from of the parallax measurement.
The satellite is going around the Earth at roughly 600 miles
up above the surface of the Earth.
It's doing exactly what the parallex is supposed to do,
when you are at a high point
like lower, and when you are at the low point in the orbit, that
is at the South Pole, you see Mercury is higher up, just as
the parallax principle. That's what leads to this
undulating signature of Mercury.
certain time apart, and you can actually get the orbit of the
satellite, which works out
So we know it works well. On the lower right is a diagram
that shows where the spacecraft is.
The red line shows the orbit
Well, the same thing should oapply to Venus..
This is the Venus transit.
the two pictures. NNotice the size of the black
dots. That's Mercury.
Venus is much thicker.
difference in size of Mercury That juand Venus.ou the
The same thing again, it shows
parallax, because the satellite the up is going around.of the
If you actually count the individual spots, the images,
which are taken every 450 seconds, you can get
the satellite, which is 97.5 minutes.
So now we come to the current transit coming up in 2012.
This is, I don't know if it's possible to dim the lights,
because this is an absolutely stunning image.
It's a composite taken by an
in Turkey. amateur astronomer, Tunc Tezel,
week, when I saw this image, and Actually, I wrote to him this
image in the presentation, asked him if I could use this
was going to be here, and his becaimages are copyrighted.ision
So I asked permission.
list on how we could use this He wrote me image.-long legal
This is taken on film, on a particular film.
There are about 27 images, I
This is the actual path of Venus believe.
It's exactly the same path that it is gracing this year, to the
day.
right is Venus next to Pleiades. So today, I think on the upper
the Pleiades. That's what Venus would've
looked like yesterday.
April 3, 2004, The exact same date,
Because Venus repeats that path in the sky, every eight years.
This is a wonderful, wonderful
Because this is a photographic demonstration of that.
absolute brightness of the composite, you can't go by the
But please notice that in the middle is the Sun.
If I could blow up this image,
see a tiny dot, which is Venus, enlarge on this image.actually
That's what Venus is doing in the sky this year.
So, this is another of his
This is Venus this year, taken images that he sent me.
by Tunc Tezel. just six weeks ago, February 25,
somewhere, in one of those This is from Central Europe
No, not European, in one of the formerly Soviet nations,
in Azerbaijan, I think. So we have seen that we can now
learn a lot more about transits from spacecraft.
The TRACE instrument, the TRACE satellite is not operating
anymore, but we have two other
Satellite, and STEREO, satellites, the Solar Dynamic
two. spacecraft, which is actually
coming transit in June this They are goiyear. observe the
But what about Venus? You know, I mean, so far, all of
these transits have focused on
Astronomical Unit, but very hlittle about Venus itself.
I think something that happened in 2004 is going to change that.
A pair of French amateur
Rondi, built a conograph. astrA conograph is just anvain
instrument, a little device,
you can see what's around it. thPeople use it frequently.so
In a sense, what happens during a total solar eclipse is what a
conograph does. The Moon blocks the Sun, so you
can see the photosphere and all the beautiful rays and --
emitting from the Sun.
their picture looks like. TActually, this is a composite,
but I have three of their animations here that you can see
moving. Perhaps the one at low right is
the most useful one.
edge of the Sun. The black curved disc is the
that's why it appears dark. You can just see the edge of the
Sun in bright light.
little circular arc. In the middle, you'll see a
The same view is shown in the colored portions in this red and
green illuminated disc. But if you observe it carefully,
you'll notice that the peak brightness changes location
around atmosphere on Venus. Now that was a chance
observation that really was not possible even from the
spacecraft observations from
So these data, just in the last two years, were used to find out
something about Venus itself, for the first time since we
began looking at the Venus
That is, that in one instant, we transits.
temperature structure all the way around Venus, along that
boundary. That's something we cannot
obtain any other way, by any
know of. spacecraft or anything that we
has excited us immensely. In the upper left, you see two
transits. You see the International Space
Station and Venus.
the change in the atmosphere After the amateurs discovered
and looked at -- Venus brightness, people went back
I don't know if you can see it and that's shown at the right.
least I can see it on my screen that there is an arc, and you do
see the difference in the brightness.
The difficult thing about TRACE observations is that the
instrument is designed to observe the Sun, it's not
designed to observe Venus.
brightness of the Sun and the So refracted light, the muchense
diminshed light that gets refracted through,
that atmosphere of Venus. So that's the beauty of the
conograph.
of scientists who met in the So last month, there was a group
same room where the were in 1874 Paris Observatory, in the very
where the expeditions were --. and 1882 transits were --,
room in the Paris Observatory, And then in the main council
look up, you'll see that it's a round room, and if you
You'll see Venus and you'll see the Sun, the chariot to the
left. At the bottom, you'll see a
telescope on Venus. And then up near the edge on the
right, you'll see the transit of
We line this years observations under the watchful eye of Louis
XVI, who is in the middle bottom
In the uppper left, is the group picture.
from Japan, from Europe, from of scientistthe US.had gathered
So we are planning these
various sites around the world. There'll be one in Norway, one
in Japan, at least one in India,
If we can find enough people or travel support, we'll send one
to Hawaii.
observations of Venus --. These observations actually are
not during the the transit. They actually get all of the
information before Venus enters the disc of the Sun and after it
exits the disc of the Sun.
refracted through the atmosphere So you have all the light
So here's a little list of the of Venus from the Sun.
the web to learn more about the transit of Venus and what they
have told us. If you come across John Philip
Sousa's march, "Transit of
There's also an opera on Venus," you can enjoy that.
The poor fellow had a terrible Gentil's life.
He did not know if I'd have enough time to show it all.
But he had taken off in 1761
He traveled all the way to from France.
fort there. InBy the time he arrived, thata
fort had been taken over by the British, so he could not land.
So he had to observe the transit
not make any useful from a boobservations.o he could
Instead of going back to France,
territory and sailed around for eight more years, until 1769,
when the French had re-taken the
the transit from India in 1769.
The next transit in 1882, an
to India, but they did something Italian team had also traveled
before. dThe Black Drop Effect was thene
main problem, as I mentioned
The Italian team thought that if earlier.
might be able to get away from they used special filters, they
So they actually used the a spectograph.ect.
They imaged Venus in different
but they were not able to get away from the Black Drop Effect.
In a sense, that Black Drop Effect happens because of
the -- Sun, and the instrumenal aberrations,
so it really messed up the
the Astronomical Unit puntil this century.of
Thank you all for coming. [applause]