sidereal year

Examples of sidereal year in the following topics:

• Kepler's Third Law

• Geomagnetism

  • If Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years.
  • The geomagnetic field changes on time scales from milliseconds to millions of years.
  • At present, the overall geomagnetic field is becoming weaker; the present strong deterioration corresponds to a 10 to 15 percent decline over the last 150 years and has accelerated in the past several years.
  • Reversals occur at apparently random intervals ranging from less than 0.1 million years to as much as 50 million years.
  • The most recent such event, called the Brunhes-Matuyama reversal, occurred about 780,000 years ago.

• World Energy Use

  • World energy consumption is the total amount of energy used by all humans on the planet (measured on a per-year basis).
  • The United States alone uses 24% of the world's oil per year, yet it makes up only 4.5% of the world's population!
  • In the last 50 years, the global energy demand has tripled due to the number of developing countries and innovations in technology.
  • It is projected to triple again over the next 30 years.
  • In China, two thirds of the energy used each year is from commercial coal energy.

• Half-Life and Rate of Decay; Carbon-14 Dating

  • It uses the naturally occurring radioisotope carbon-14 (14C) to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years old.
  • Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14.
  • The carbon-14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with molecules of nitrogen (N2) and single nitrogen atoms (N) in the stratosphere.
  • Raw (i.e., uncalibrated) radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), with "present" defined as CE 1950.
  • Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby at a seminar in Chicago that year.

• Natural Radioactivity

  • The worldwide average natural dose to humans is about 2.4 millisieverts (mSv) per year.
  • This is four times more than the worldwide average artificial radiation exposure, which in the year 2008 amounted to about 0.6 mSv per year.
  • An airline crew typically gets an extra dose on the order of 2.2 mSv (220 mrem) per year.
  • Because of this, the present activity on Earth from uranium-238 is only half as much as it originally was because of its 4.5-billion-year half-life.
  • Potassium-40 (with a half-life of 1.25 billion years) is at about eight percent of its original activity.

• Global Warming Revisited

  • The Second Law of Thermodynamics may help provide explanation for the global warming over the last 250 years.
  • The Second Law of Thermodynamics may help provide explanation for why there have been increases in Earth's temperatures over the last 250 years (often called "Global Warming"), and many professionals are concerned that the entropy increase of the universe is a real threat to the environment .
  • The black line is the annual mean and the red line is the five-year running mean.

• Beta Decay

  • One example is the odd-proton odd-neutron nuclide 40 K, which undergoes both types of beta decay with a half-life of 1.277 ·109 years.
  • In this video I introduce Beta decay and discuss it from an basic level to a perhaps second or third year University level.
  • In this video I introduce Beta decay and discuss it from an basic level to a perhaps second or third year University level.

• Calculations Involving Half-Life and Decay-Rates

  • A sample of 14C, whose half-life is 5730 years, has a decay rate of 14 disintegrations per minute (dpm) per gram of natural carbon.
  • We have: $N = N_o e^{-t/\tau} \text{ where } N/N_o=4/14≈0.286 $, $\tau = t_{1/2}/ln2 \approx 8267 \text{ years, } t=−\tau lnN/N_o≈10360 \text{ years.}$
  • Half-lives of known radionuclides vary widely, from more than 1019 years, such as for the very nearly stable nuclide 209 Bi, to 10−23 seconds for highly unstable ones.

• Back to Maxwell's Equations

  • The aether was originally proposed by Aristotle and experiments agreed with it for about 2,200 years, so throwing it away was a big deal.

• Medical Imaging and Diagnostics

  • Higher doses can cause varying side effects during treatment (acute), in the months or years following treatment (long-term), or after re-treatment (cumulative).