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Brane power to the max, cont

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Because nearly every thing we derive in astronomy depends on knowing the distance. ... with the change in the cosmic scale, this solved a riddle in astronomy. ... – PowerPoint PPT presentation

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Title: Brane power to the max, cont


1
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
2
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?

3
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?

4
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?

5
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.

6
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.

7
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.

8
  • 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.

9
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.

10
  • 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?

11
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
12
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.

13
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

14
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!)
15
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
16
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.

17
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.

18
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.

19
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).
20
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.
21
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!
22
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!
23
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

24
Fun animation on how standard candle works
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