The sun gives off energy all of the time. This is the energy that all life
uses to grow and live; whether directly (as photosynthesis by plants) or
indirectly (as herbivores and carnivores that consume the energy stored in
living things). Without that energy source, the Earth would be a dark,
cold, lifeless place. So, it is certainly of interest to ask "Will the
Sun be there tomorrow?", or, more usefully, to ask when the sun will stop
shining. In other words, how long will the sun last?
The goal of this homework assignment is to answer that question. > The Sun formed from a spinning cloud of gas through gravitational collapse. The planets formed at the same time. So the ages of the planets provide a good estimate of the age of the Sun: 4.5 billion years. The Sun has been shining brightly, at almost exactly the same rate (a constant luminosity), for 4.5 billion years. This implies that it has been producing energy at a constant rate for those 4.5 billion years.
Mass of 1 Hydrogen atom: 1.673 x 10-24 grams Mass of 1 Helium atom: 6.644 x 10-24 grams
- Luminosity - energy per second; usually the total energy given off by an object per second.
- 1 Watt = 107 ergs/sec
- 1 Solar Luminosity = 3.89 x 1033 ergs/sec
- Energy - Bah. Try and define that. Usually measured in ergs; an erg is about the energy of one flea jump.
- 1 erg = 1 gm*cm2/sec2 = 10-7 joules
- [if you use E=mc2 with the mass in grams, the speed in cm/sec, then you get E in gm*(cm/sec)2, which is gm*cm2/sec2 = ergs]
- Mass - the amount of matter. Usually measured in grams, or solar masses.
- 1 solar mass = 1.989 x 1033 gm
- 1 hydrogen atom = 1 proton = 1.67352 x 10-24 gm
- Speed - velocity; distance traveled per time unit. Measured in lots of units; We'll use cm/sec because of the definition energy in ergs
- Speed of light = c = 3.00 x 1010 cm/sec = 300,000 km/sec
- Time - measured in seconds, days, months, years.
- 1 year = 3.15 x 107 seconds