Brane power to the max, cont

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Brane power to the max, cont
Besides the existence of another universe, BPM
has two special features (at least) 1. We wont
find and non-baryonic dark matter because there
isnt any. Rather the gravitational interaction
with the other Universe mimics this effect. 2.
We wont find gravitational radiation
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General Considerations continued

• How long is it going to take me?

• How much is it going to cost?

• Are the time and money worth it?

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Other Considerations

• When to holdem and when to foldem

• What are the cost drivers in my design?

• Do I need any instrument development to allow me
  to achieve my goals?

• Do I have all the skills I need?

• If not, can I assemble a winning team?

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Technical Considerations

• What limits the accuracy of my measurement?

• How will I calibrate my measurements so that
  somebody else can judge the results.

• What assumptions will I have to make from theory
  or experiment to build my case.

• If Im looking for an effect (such as WIMPs),
  will my result be interesting even if I dont
  find the effect?

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Why Distance

• Why bother with the distance scale?
• Because nearly every thing we derive in astronomy
  depends on knowing the distance.
• For cosmology, we want to know
• The expansion rate (Hubble constant) which
  requires distance versus velocity measurements.
• We want to measure the mass density of the
  universe, we need to know the mass within a given
  volume, which means a knowledge of the distance.

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Why Distance

• For cosmology, we want to know
• The distance along with a measure of the redshift
  so we can test different geometries of the
  Universe
• The distance to objects can tell us how these
  objects form and evolve.
• The spatial distribution objects is another test
  of cosmology.

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Back to distance

• Overall design calls for a bootstrap approach.
  
• Begin with small distances we can effectively
  measure with a ruler.
• Then use parallax can tell us distances.
• Parallax is the effect of noting you can discern
  the distance to an object if you can measure how
  much it appears to move around as you do.

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• Overall design calls for a bootstrap approach.
  
• We start with small distances we can effectively
  measure with a ruler.
• Next step in the design is to figure out that
  the parallax can tell us distances.
• Parallax is the effect of noting you can discern
  the distance to an object if you can measure how
  much it appears to move around as you do.

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Parallax Demo

• Take a piece of paper and draw a stripe on it.
• Hold the paper at arms length with your nose
  pointed at the stripe.
• Hold 1 finger a 1 - 1.5 feet in front of your
  nose
• Then close your left eye. Then open it and close
  your right eye. Notice how much your finger
  appears to move RELATIVE to the stripe.
• Move finger until it is almost touching the
  stripe and try again.
• Wont be much apparent motion relative to stripe.
  

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• The effect is caused by moving your vision
  relative to your finger and you have accomplished
  the motion by using different eyes.
• Same as using one eye and moving it the distance
  between you two eyes perpendicular to the
  line-of-sight.
• How far can we determine distances that way?
  Need to answer
• (1) How far apart are our eyes ?
• (2) How small a change in apparent motion can we
  measure?

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OK now what, cont.

• My eyes are separated by about 7 cm, and I know
  also I can see an angular separation of about 1
  arc minute. So the diagram I draw is like this

Using trigonometry, dsin(1.0 arc min) 3.5 cm
or d 120 meters tops, q 1 arc min.
l about d, s 3.5 cm
Apparent motion
Each right triangle has a base of 3.5 cm and the
apex angle of 1 arc minutes
q
d
l
s
eyes
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Parallax cont.

• gt If we know s and q we can calculate d (and or
  l). This give us the distance. A persons
  distance or depth perception via binocular
  vision is about 7 times worse than what Ive
  calculated about 50-60 feet (15-18 meters) .
  

(cf., http//online.sfsu.edu/psych200/unit6/66.ht
m)

• Where did I go wrong? (a) Our eye needs a
  reference frame and the reference frame should be
  distant enough not to show parallax (b) the eye
  doesnt have the luxury of being able to
  accumulate data for hours and to look at objects
  with extremely well defined centers.

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Parallax and astronomy

• Need equivalent of s to be as large as possible
  and accurately measured. gt
• Here to Chicago wont do it.
• One side of earth to the other can allow us a low
  tech way of measuring the distance to the Moon.
• Fine, but the closest star besides the sun is
  four million times further away. We need a
  larger s. This is

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Parallax and astronomy

• The Earths orbit around the sun!

• Our most accurate measure now is by?

Radar!
And 1 arc second for q in our diagram with the
earths motion around the sun to define s, we
find that 1 arc second gives a distance called a
Parsec (for parallax and arc second!)
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The parsec
Taking s 1.50 x 1013 cm and q 1 arc second
and sin(1 arc second) 4.85 x 10-6. Or, d
(1.50 x1013)/(4.85 x 10-6) 3.09 x 1018 cm! Or
in round numbers, 3 x 1018 cm 1 par sec. A
year p x 107 sec of timegt p x 107 sec x 3 x
1010 cm/sec 1018 cm, or 1 par sec about 3
light years, where speed of light c 3 x 1010
cm/sec
1 parsec (pc) 3 x 1018 cm
3 light years 1 parsec
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But will parallax work beyond the stars in our
galaxy?

• NO! gt We need to determine parallax to a
  standard candle, if we can get it.

• What do we need? Precise, small images, the
  better to find the centers of, and a well defined
  non-moving background for reference.

• Stars are good for making small images, and
  distant stars or small galaxies are good for
  reference.

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Limitations to parallax method

• Swing around sun Going to Pluto would get us a
  much larger swing, but the period is over 200
  years!

• Image quality Rule of thumb is we can measure a
  center to about 1/10 of an objects width. The
  best we could do on the ground a few years ago
  was 0.5 arc second images gt about 20 pc
  distance. If can go into space can get a factor
  of 100 improvement without the blurring effects
  of the Earths atmosphere.

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Limitations to parallax method

• Swing around sun Going to Pluto would get us a
  much larger swing, but the period is over 200
  years!

• Image quality Rule of thumb is we can measure a
  center to about 1/10 of an objects width. The
  best we could do on the ground a few years ago
  was 0.5 arc second images gt about 20 pc
  distance. If can go into space can get a factor
  of 100 improvement without the blurring effects
  of the Earths atmosphere.

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Hipparcos, the ultimate solution
Hipparcos is an acronym for HIgh Precision
PARallax COllecting Satellite. Appropriately the
proununciation is also very close to Hipparchus,
the name of a Greek astronomer who lived from
190 to 120 BCE. By measuring the position of the
Moon against the stars, Hipparchus was able to
determine the Moon's parallax and thus its
distance from the Earth. He also made the first
accurate star map which lead to the discovery,
when compared with other data from his
predecessors, that the Earth's poles rotate in
the sky, a phenomenon referred to as the
precession of the equinoxes. The concept of
using the data recorded by the star mappers for
astrometric and photometric observations was
conceived by Erik Høg, a Danish astronomer
involved with the Hipparcos mission. It was
fitting that the catalogue which resulted from
the star mappers should then be named after
Tycho Brahe, a 16th century Danish astronomer,
who produced the first 'modern' star catalogue
(1602).
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Hipparcos Instrument
Main optic a mirror only 29 cm wide! For
comparison, HST is over 200 cm wide.
Being above atmosphere and having clever designs
of a mask (think if knife edge test) to overcome
the small mirror size so as to yield 100 times
better star positions than could be done from the
ground.
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Hipparcos, the ultimate solution
Scientists now possess, for the first time, a
good three-dimensional picture of the bright
stars in our neighbourhood. Hipparcos measured
the distances of many stars, which were
previously a matter of guesswork. For example
Polaris, the Pole Star, is 430 light-years
away. Hipparcos hit the headlines in 1997 when
it showed that the chief measuring rod for the
Universe was wrongly marked. Bright blue stars
called Cepheids, of which Polaris is one, vary in
luminosity in predictable ways. Astronomers use
them to gauge distances of galaxies and the scale
of the cosmos. But Hipparcos revealed them to be
farther away than previously supposed. This made
the Universe about 10 percent older. Also farther
away than expected are the oldest known stars,
the so- called halo stars. The change in
distances cut their ages by a few billion years.
Combined with the change in the cosmic scale,
this solved a riddle in astronomy. Before
Hipparcos the old stars seemed to predate the
Universe. That was as nonsensical as mountains
older than the Earth!
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Bottom line we now have (1) a ruler measurement
to the sun and astrometry to give us accurate
positions to the (2) A satellite dedicated to the
boring, tedious task of accurately measuring
star positions to yield accurate (to the few
percent level) the distances to Cepheid
Variables. And Cepheid Variables are our closest
standard candles and they are bright enough to be
seen out to nearly 20 Mpc where we can overlap
with other things!
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What are Cepheid Variables

• Cepheids are unstable (on human time scales)
  stars with cycles of 1-50 days. And the longer
  the period the intrinsically more luminous they
  are gt

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Fun animation on how standard candle works