Before the TESS or
Kepler space missions,
I was part of a team that searched for transiting exoplanets
using backyard telescopes fitted with CCD cameras. We would sift through candidate stars that appeared to have
periodic variation in brightness. Mostly, we found Delta Scuti pulsating variable stars. Lots of them. But then
one night, two of us independently observed the same star and we each saw the same telltale lightcurve of a transiting planet. We had found
our first exoplanet, dubbed XO-1.
Amateurs and small-scope astronomers still have a great deal to contribute to the field and I am still interested
and involved in doing photometric measurements. Large scopes and space-based
missions are not well-suited to find long period transiting planets (a year or more). Crucially, there are now quite a few
known multiplanet systems that, like the Solar System, likely have more planets. Also, studies looking for star spots and their
temporal evolution are intriguing.
I am a member of Southern Maine Astronomers (SMA), an amateur astronomy club. SMA meets monthly at the Southworth Planetarium
at USM in Portland. A typical meeting has a featured talk, a short planetarium view of the current sky and interesting
objects that are currently visible, and of course hobnobbing. We also put on star parties from time to time often in association
with a non-profit organization or school.
While it is possible to simply look at pictures on websites or in books, it's hard to beat seeing something that is millions of
parsecs away with your own eye.
Astrophotography is the art of taking a low-noise, very long exposure image of an invisible moving object
at night while tracking the object at sub-arcsecond precision.
Shown on the right is an image I made of the Pelican Nebula in Cygnus near the star Deneb. It is an
HII region which glows in the
light from hydrogen recombination (notably the
Balmer 3-2 or H-alpha line at 656.3nm)
plus the forbidden [OIII] line at 500.7nm and
the forbidden [SII] doublet at 671.6/673.1nm. Narrow passband filters captured each of those emission lines separately,
and were then assembled as an RGB image in false color.
FUN FACT: The [OIII] line was first observed spectrographically in astronomical nebulae in the late 1800's. Because the forbidden transition (not
really forbidden after all) is slow, no Earth-based vacuum is good enough to avoid de-excitation through collision first.
Since no known element had a laboratory spectral emission line corresponding to [OIII], it was speculated that a new element
had been discovered that existed only in nebulae. This ersatz element was dubbed Nebulium! You can find references to Nebulium
in old astronomy textbooks.
Below is an image of Bode's Nebula, aka M81 in Ursa Major. It is a composite of an RGB broadband image with an H-alpha overlay that
highlights the HII regions in the arms of the galaxy where there is star formation.
Find a really big parking lot and then set up a course with traffic cones. Next, get in your
car and go as fast as you can. It's a blast, the turns come fast, and it is quite challenging to record a respectable time.
The single biggest variable is the driver. By far. Of course, the car does make some difference which leads to thinking about
the physics of tuning a car to make it more nimble.
Here's a clip of my son Ben (who has become quite a good racer, often finishing in the top tier):
POWER: Probably one of the least impactful variables, but it *does* help to have better acceleration. My son Ben races with a 1992 Miata,
as I did when I had one. It's native power to the wheels is around 100HP (the car is very light, so that's more than it might seem). But being gearheads,
we want more. We installed a turbocharger which is basically a high speed air pump. The goal is to increase the amount of oxygen entering each engine cylinder
per stroke. That is achieved by the compression - we get about 15PSI of boost, or about twice atmospheric pressure. From the
ideal gas laws, we know that all this
compression will raise the temperature of the air - a lot. Power is extracted when we have a
delta-T, and hot air is less dense, so this hot air is bad.
Therefore the next stage is an air-to-air intercooler which you can see in the photo (it looks like a radiator).
To maintain stoichiometry, the car has a wideband O2 sensor to smell the exhaust which tells a custom controller how much fuel to inject via closed-loop
feedback. Because we have doubled the amount of available oxygen, the stock fuel injectors aren't up to the task at full power. So,
higher flow injectors were installed. The result is a little ove 200HP to the wheels (about 250HP at the engine).
All this extra power (and more to the point, torque)
is no good if the clutch slips. Accordingly, the car has a stiffer pressure plate and
a high performance clutch disk.
CHASSIS: Miatas are blessed with a fully independent double-wishbone suspension
at all four corners. That's as good as it gets. To limit body roll, the car has custom springs with a higher
spring constant. To ensure that the car
returns to equilibrium quickly without oscillation, it is necessary to reduce the Q of the
harmonic oscillator formed by the springs and the car mass. This is achieved by using shock absorbers with greater dampening. Brakes work by turning kinetic energy
into thermal energy. When autocrossing there is a lot of energy to be dissipated (a higher average
power), so the car has upgraded disk brake rotors and brake pads.
DRIVING TECHNIQUE: It's mostly about free-body diagrams and the fact that we only have about 1g available due to the
coefficient of static friction between the tires and the road (the 'grip').
The trick is to mete out the available grip where it is most useful at the time.
Consider the execution of a turn: We approach a turn at a speed that is intentionally higher than we can maintain in the turn. By applying the brakes, the car
slows, but there is another benefit. An additional downward force component is transferred to the front tires increasing their grip making a higher
lateral force available at the front of the car by turning the wheels. This is the moment to begin
the turn to overcome the rotational inertia of the car about the z-axis (otherwise the car will 'plow' and turn slowly, if at all). Once the rotation of the car
has been established, braking is relaxed making the available grip fully available to maintain the car on its (approximately circular)
trajectory. Note that the coefficient of static
friction is generally higher than the coefficient of sliding friction, so the goal is always to avoid any sliding or skidding. It may look cool, but it is slow. Upon
exiting the turn, one accelerates to the next one.
Finally, one must anticipate the turns and see the virtual apex. Being late on a turn can have a cumulative effect, as all slalom ski racers know.
In the end, driver technique tends to dominate.
