On 5/10/18 9:55 PM, Hal Murray wrote:

The whole area of celestial nav is time related and uses very simple
equipment -

Telling time by measuring the sun in some way.  Occultation of stars by
the moon.  Positions of jupiter's big 4 moons.

Pendulum experiments.  If the student has a way to change their
altitude, can they measure changes in g.  Driving a pendulum.

Coupled resonators  (spring/mass, pendulum, vibrating rods)

Measuring the speed of light (Fizeau or Michelson method? Other ways)

Water clock, sand hour glass, etc.  Measuring performance variation over
environmental variations.

the trick with good science projects is finding something that's not
just a "lab demo" - where there's some engineering component to figuring
out how to execute the demo with unusual or improvised equipment, or
where you're measuring something that's not been done before.

For instance, measuring time with Jupiter's moons has been done for
centuries, but has it been done by taking cell phone pictures through a
telescope and then measuring the distances on the resulting images?
Can you make a sundial with a webcam pointed at a spherical reflector
(to make an "all-sky camera")

Other experiments play off a old joke - there's one about "how to you
tell how tall a building is using a barometer"  - take it to the top of
the building drop it, and time how long it takes til it hits the ground.
Build a pendulum the height of the building, using the barometer as a
pendulum bob.

Characterizing a clock is a good one -
a) there's well developed analytical tools for doing the data reduction
(AVAR, etc.)
b) the experiment lends itself to collecting multiple data sets from
multiple instances of the clock in question
c) clock performance is affected by environment, so there's lots of
potential experiments.

Hi

NTP time offsets through various phases of the distribution process …..

Bob

On 11/05/2018 07:23, jimlux wrote:

The advice that we got when doing a middle school science project was
that you wanted an experiment with only one variable (altitude or
temperature etc) and a  measurement of a single variable (maybe over time).

Philip

How about measuring variations in propagation delay for WWV on various
frequencies, or WWVB,
using GPS ticks as a reference.

Dana    K8YUM

On Fri, May 11, 2018 at 9:41 AM, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

On 5/11/18 7:07 AM, Philip Gladstone wrote:

and with multiple measurements possible - most middle school projects
tend to be a "one and done" - you get big kudos if you show even basic
statistical analysis - a simple significance test is a big deal,
assuming you're not doing it with some cookbook calculator.  You'd need
to be able to explain what it means to the judges.

And something where you show an appreciation of measurement precision
and any curve fit.  I used to mark down projects where they used Excel
to do a regression curve, and then reported the coefficients with 5
digits of precision, on measurements with at most 2 digits. (and no, not
thousands of measurements to get a sqrt(N) improvement)

AVAR is a kind of sophisticated concept - I think it would be hard for a
middle schooler to adequately explain what it is (heck, there's enough
trouble for people who do it for a living).

David.vanhorn wrote:

My favorite exhibit that we never see anymore.   IIRC it was a quarter
mile of fiber and a green laser.  And ISTR that the disc had one hole on
one arm and two radially on the other, but I can't remember why.  I
thought that the light would pass through the same hole twice, once on
the way in and on the way out when that same hole rotated 180 degrees to
the other end of the fiber.  The disk spun somewhere around 50 rps (60
with an AC motor?).

--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel.  -Crow on solitaire

On 5/11/18 9:08 PM, Jeff Woolsey wrote:

1km in free space would be 6 microseconds round trip. I'm not sure a
disk spinning at 3600 rpm would work.  you'd need to have the "hole
spacing" be on the order of 6 microseconds - and at 100 rps (6000 RPM),
10 ms/rev, you'd need the sending and receiving hole 6/10000 of a rev
apart (about 0.2 degrees).

if you had 10 km of fiber, it would be a bit easier.

Hi

I think the term “long fiber” in this case should really be “very very long”.  Exactly how the typical student
funds the acquisition of something in the “many miles” range, I have no idea.

You could use an optical grating of some sort as your “spinning disk”. The end of the fiber is going to be
mighty small. The spacing on the grating could be quite tight. Where you get a circular part like that ….
again no idea.

Bob

It may  be that a nicely-written request to Corning could yield the loan of
a big spool of fiber
for the duration of a science fair project.

Another alternative, perhaps easier to implement, might be an
electrically-driven light modulator
at the detector end.  For the source, an LED or diode laser is easy to
modulate at respectable
rates.  This approach should allow use of such high frequencies that an
open optical path using
mirrors might even suffice.

Or here's an intermediate scheme:
If one were to use two modulated sources (or one with a beamsplitter), with
one path delayed
by the long(ish) fiber and the other by a minimal-length local fiber,
something resembling a streak
camera (implemented with a rotating mirror) might permit use of
substantially higher pulse rates
than with a rotating disk, without incurring the need for anything very
fancy in the way of mechanics.
Only the modulated source should require a reasonably accurate drive
frequency- the "detector"
would be essentially self-calibrating.  A small mirror, say of cm size,
could probably be safely
rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
resolution is attained,
this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
(approx 750 ns one-way delay)
should yield an angular separation of nearly five "dots" between delayed
and undelayed dots.
And if the sources are modulated at a rate such that a few pulse
repetitions are visible in the
field of view, the scheme is self-calibrating as long as the PRF and the
velocity factor in the fiber
are known.  Probably the only precision work would be the optics required
to focus a reasonable
amount of light from the source(s) onto the two fibers., and I believe this
requirement could be
adequately met with microscope objectives borrowed from one's school's
biology lab.

A fly in the ointment is that if ordinary (read, inexpensive) IR fiber is
used at convenient visible
wavelengths, propagation will occur in more than one spatial mode, with
different modes propagating
at different speeds.  I don't know how much of a problem this would
raise.  But it may be that if
tweaking of the transmitting end illumination is done, both in angle and
transverse position, most
of the propagating light could be confined to a single mode.  I speak of
visible wavelengths simply
because using these avoids the cost of electronic detectors, oscilloscopes,
etc, potentially saving
a lot on the cost of the experiment as well as making for a more satisfying
presentation.

Dana

On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq kb8tq@n1k.org wrote:

Like this so called star target?:
https://www.edmundoptics.com/test-targets/resolution-test-targets/1-black-1-white-glass-star-target-5deg-wedge-pair-angle/

Bruce

Even with single mode fiber its finite group delay dispersion will likely restrict the usable light source bandwidth.

Bruce

Indeed; however, with single mode fiber the limit is not too bad.  At
Arecibo we routinely ran bandwidths in
excess of 1 GHz through fibers of about 1500 ft length with no problems.
For the science fair project a
bandwidth of a few MHz should suffice for lengths of, say, 500 ft.  It's
just that I don't know how bad the
multimode dispersion problem would be when using shorter wavelengths, and
I'm sure not equipped to
make any measurements at home now that I'm retired and far away from the
observatory.

Dana

On Sat, May 12, 2018 at 5:44 PM, Bruce Griffiths <bruce.griffiths@xtra.co.nz

How about a demonstration of how GPS works, substituting sound waves for
radio ?

Maybe three sound sources with harmonically-related frequencies, then
measure their phase difference on an oscilloscope.

Cheat a bit : you don't need to do cdma acquisition. Have one reference at
a low frequency, switch two more on alternately at a higher frequency.
Measure the phase difference between one pair at a time and calculate your
location relative to the stationary sources.

On Sun, May 13, 2018 at 12:31 AM, Dana Whitlow k8yumdoober@gmail.com
wrote:

At telecom wavelengths GDD can be quite low.
Laser source spectral widths can also be low.
At visible wavelengths an fiber length imbalance of 1m with a 1nm bandwidth light source makes interferometry impossible/difficult without GDD compensation even if delays are matched.
The moodulation bandwidth isnt an issue for this application but with a long enough fiber the source spectral bandwidth may be.
Polarisation locked single transverse mode VCSELs are inexpensive and typically have spectral bandwidths of 100MHz or so.

Bruce

On 5/12/18 5:01 PM, Adrian Godwin wrote:

In science fairs that are judged, the rubric really demands something
that can be cast into the classic "literature search, hypothesis,
experiment, data reduction, conclusion" form.  Even straight up
engineering is sometimes knocked down - the International Fair (being
held this week, as it happens) does have separate rubric for engineering
projects.

So what you want to do is cast this as an experiment or engineering
project.  For the latter: "Performance characterization of acoustic
multilateration"

For a more "sciencey" approach, you'd postulate some theory/hypothesis:
"air temperature measurement can be used to compensate for speed of
sound variation in acoustic multilateration"

What I remember was a brown or black disc with holes around the perimeter.
I remember a lot of holes.
This was around 1991 or so.

-----Original Message-----
From: time-nuts time-nuts-bounces@febo.com On Behalf Of Bruce Griffiths
Sent: Saturday, May 12, 2018 4:39 PM
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Subject: Re: [time-nuts] Anybody have suggestions for time related science fair projects?

Like this so called star target?:
https://www.edmundoptics.com/test-targets/resolution-test-targets/1-black-1-white-glass-star-target-5deg-wedge-pair-angle/

Bruce

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On 5/14/18 1:00 PM, ed breya wrote:

Even at the middle school level, science fairs can be quite competitive

• The California Science Fair draws hundreds of projects at that grade
  level (Grade 6-9) selected from fairs at the county level, which in turn
  draw from school fairs.

The standard of judging is quite rigorous - a "demo" won't generally be
competitive at the state level, although it could make it through the
county level - depending on the county.

Virtually all science fairs prohibit lasers in a display - too many "bad
things" happening with remarkably high powered lasers available online.
You'll need to show it cannot be operated, or that it cannot present a
hazard (i.e. if it's built into a piece of hardware that cannot be
modified on site to allow exposure).

Even laser pointers are not allowed (because how is the display review
committee to know whether it's 1 mW or 100 mW)

A strobe is a fine display, and there's probably interesting time-nuts
kinds of experiments one can do using it - the combination of a short
duration strobe with a modern cellphone camera running at, say, 240 fps,
might be a good way to instrumentally measure a mechanical vibration.

But you need to have some set of experiments designed to confirm or
reject a hypothesis. You could have a hypothesis about synchronization
of vibrating rods on a common base, for instance.