The next calendar (click for hi-res image). Lots of anniversaries coming up, including 100 years since the eclipse test of general relativity and 40 years since the movie Alien. Also, the new SI units come into force.
See more calendars here.
On May 20, a major redefinition of SI (metric) units comes into force. In particular, the second, metre, ampere, mole, kilogram, kelvin, and candela will be defined as follows:
As it is now, the second will be defined using ultra-precise caesium clocks. Specific microwave radiation from caesium atoms is defined to have a frequency of exactly 9.192 631 770 GHz. That is, counting 9,192,631,770 waves will take exactly one second.
As it is now, the metre will be defined using the speed of light, which is defined to be exactly 299,792,458 metres per second. That is, the metre is the distance travelled by light in one 299,792,458th of a second (where the second is defined as above).
The definition of the ampere (amp) has been greatly simplified, taking account of the connection between electricity and electrons. The ampere is a coulomb of electric charge flowing past a given point per second, and the charge on a single electron is now defined to be 1.602 176 634 × 10−19 coulombs. Thus an ampere is about 6,241,509,074 billion electrons flowing past a given point in a second.
As a consequence of this new definition, two important natural constants which used to have defined values (the permeability of free space and the permittivity of free space) now have experimentally determined ones. This will require rewriting pretty much every physics and electrical engineering textbook.
The mole represents Avogadro’s number of atoms, molecules, or other particles. Previously, Avogadro’s number was defined to be the number of carbon atoms in 12 grams of pure carbon-12. It is now defined to be exactly 6.022 140 76 × 1023.
Until 2019, the kilogram was defined by the mass of a specific metal cylinder held in Paris. This has been felt to be unsatisfactory for many years. The current definition uses the fact that the energy of a light photon (in joules) is its frequency times Planck’s constant h, which is defined to be exactly 6.626 070 15 × 10−34.
In practice, a Kibble balance will be used to measure weights by balancing them against an electrically produced force. Units derived from the kilogram include:
See also what NIST has to say about the kilogram.
Temperature in degrees Celsius was originally measured on a scale with 0 °C being the freezing point of water and 100 °C the boiling point (at standard pressure). The lowest possible temperature turned out to be absolute zero, −273.15 °C. In 1954, the two fixed points on the scale were changed to −273.15 °C (0 kelvins) and the triple point of water, 0.01 °C (273.16 kelvins).
This definition proved unhelpful for calibrating thermometers intended for very high temperatures, and the current definition uses the fact that the average translational kinetic energy (in joules) of a moving atom of a monoatomic ideal gas is (3/2) k T, where T is the temperature of the gas in kelvins, and the Boltzmann constant k is defined to be exactly 1.380 649 × 10−23.
The definition of the candela remains what it has been, except that it is influenced by the change in definition of the kilogram (and hence the watt). A light source that emits monochromatic yellowish-green light at a frequency of 540 THz (roughly 555 nm wavelength) is taken to emit 683 lumens per watt, and a light source that uniformly radiates 1 candela in all directions has a total luminous flux of 4π lumens (the constant 683 reflects the human ability to perceive light). The lux is a lumen per square metre.
When the metric system was first introduced, the metre was defined in terms of the world (1/10,000,000 of the distance between the Equator and the North Pole, measured via Paris). Today, the metric system carries that philosophy to its ultimate conclusion, with all units except the candela defined in terms of the universe. Five of the units are defined in terms of fundamental physical constants: the speed of light (first measured by Rømer in 1676), the charge on the electron (first measured directly by Robert A. Millikan in 1909), the Avogadro constant (measured several ways by Jean Perrin around 1910), and the Planck and Boltzmann constants (first defined by Max Planck around 1900).
The redefined metric system is a little difficult to grasp without understanding modern physics, but fortunately most of us will just keep on using exactly the same measurement instruments as we have done for years.
Here is a further update on the 51 teams (27 Challengers, 23 Cruisers, and 1 Adventure car) aiming for the 2019 Bridgestone World Solar Challenge in Australia this coming October. Many teams are busy with construction, and below is my best understanding of the current team status (it does not yet reflect the to-be-published official list of teams).
Meanwhile, 26 teams – Bridger, Calgary, CalSol (1st in 2017), Esteban (3rd in 2017), Florida, Ga Tech, Illini, Illinois St, Kentucky, Mich St, Missouri S&T, NCSU, NJIT, Northwestern, Principia, PrISUm, Purdue, Rutgers, SIUE, UBC, UPRM, USC, UT, UVA, W Mich, and Waterloo, including 1 WSC team – are preparing to attend FSGP 2019 in America this July.
Challenger (Lumen II) – they have been doing a lot of testing.
Challenger (new car: MTAA Gnowee) – the car is named after a woman in Aboriginal myth who carries the sun.
Cruiser (Investigator Mark III) – they are planning to improve aerodynamics, reduce weight, and make some other changes.
Cruiser (SAV) – this time they will tow the trailer that belongs with the car.
Cruiser (ArrowSTF) – as well as racing, their commercial arm, Prohelion, is selling power packages.
Challenger (new car) – they won the American Solar Challenge last year (with their Challenger car Unlimited 2.0).
Challenger (Éclipse X.I) – they came an excellent 3rd in the ASC, 102 minutes behind Western Sydney, and hope to go even faster with the new battery pack in their modified car. Planned improvements are summarised in their winter newsletter.
Challenger (new car: Viridian) – they plan to unveil the new car in July.
Challenger (new car: Intikallpa V) – no news on the new design as yet.
Cruiser (new car: Auriga ) – they will be back at the WSC after coming 14th in 2007.
Cruiser (new car) – Bochum also has a solar buggy team.
Challenger (new car) – they have a car-racing game app starring their car.
Cruiser (Sophie 6 plus) – they have been working on the car body.
Challenger (new car) – no details as yet.
Cruiser (SM-S2) – existing car.
Cruiser (new car: Archimede 2.0) – they have an exciting design concept.
Challenger (new car) – they have officially announced their participation.
Challenger (new car) – no news on the new design as yet.
Challenger (new car) – in January they hosted some visitors from Lodz.
Challenger (new car) – no news on the new design as yet.
Challenger (new car: Tigris) – see their first vlog (in Bahasa Malaysia).
Challenger (new car: Eleadora 2) – their new catamaran will look like this.
Cruiser (new car: Stella ?) – they are turning a shipping container into an oven for production and plan to reveal their car on July 4.
Challenger (new car: Red E) – they are already producing regular vlogs, and have a vlog for February (Dutch only). They have revealed their design, which is a GaAs catamaran (see the animation here). They will run a MOOC explaining the design of their 2015 car.
Challenger (new car: Nuna X) – these are the champions formerly known as Nuon. See their 2017 aftermovie.
Cruiser (Eagle Two) – they have produced a solar baby, which is a prize that lasts.
Cruiser (new team) – they are ready to begin 3D-printing some prototypes.
Cruiser (new car) – no news on the new design as yet.
Challenger (new car) – they have a rolling test chassis. The body design seems long and thin.
Challenger (MDH Solar Car) – they have been doing some testing.
Challenger (SER-3) – they raced this car in South Africa.
Cruiser (new car: Apollo IX) – they have been making some carbon-fibre seats.
Cruiser (new car: STC-3) – no news on the new design as yet.
Challenger (new car) – they expect the new car to be 44% more efficient than the 2015 model.
Cruiser – this high-school team came 6th in the iESC Cruiser class.
Challenger (new car: Ortus) – they have begun fabrication.
Cruiser (new car: Tachyon) – they have a bottom shell and roll cage. They will also attend FSGP 2019.
Adventure (Sundancer) – this high school team from from Houston, Mississippi is a regular visitor, because they keep winning the US high school race.
Challenger (new car) – they have revealed their shell, which is a unique asymmetric bullet car.
Challenger (new car) – they are asking for name suggestions for the new car.
Cruiser (new car: Freya) – no news on the new design as yet.
This page last updated 19:37 on 8 April 2019 AEST
I could have cropped the face a little better, but bad photoshopping is part of what memes are all about.
Thanks to the Griner family, of course.