Amazing Cassini Movie

A colleague pointed out this movie on the Astronomy Picture of the Day. Check it out.

Mercury, MESSENGER and Jupiter

Stellarium's View to the West on March 15

On March 18, the MESSENGER spacecraft will end a orbit around the planet Mercury.  MESSENGER was launched in August 2004, so it has had a long journey with one Earth fly-by, two fly-bys of Venus and three of Mercury.   MESSENGER's primary mission will last until March 2012 and it will photograph the surface with a resolution of 250 meters.

Coincidently just five days later Mercury will reach its maximum angular distance from the Sun, so it will appear as an evening star for a while after sunset.   A couple of days earlier, Mercury will pass within a couple degrees on Jupiter on the sky making it even easier to spot.

Over the next few weeks we can look forward to lots of new photos of the surface of Mercury from the first spacecraft to orbit the innermost planet and perhaps some great photos of its conjunction with Jupiter as well.

Do CFLs Make Sense for BC?

A Compact Fluorescent Bulb (Wikipedia)

I recently noticed that BC has banned 75W and 100W incandescent light bulbs.  I was just wondering whether BC actually needs to legislate a more efficient light bulb, or whether it is even more efficient for many applications.  I'm not going to go into the aesthetics of the light from CFLs versus incandescents.  Frankly I doesn't bother me but I do appreciate that it bothers lots of people.  Rather I would like to look at the energetics.  

The basic assumption is that the heat produced by light bulbs is an inefficiency.   This is clear if you have lighting in a space that is air conditioned, but it isn't so clear in a space that you heat (at least not to me).  BC is not nearly as cold as other portions of Canada but it isn't Arizona either.  The times that we use lighting happened to coincide with the times when we use the heating, so the heat generated by the light bulbs actually slightly reduces the energy required by our boiler to heat the house.

I'm not the first to point this out.  I would suggest that you look at the CBC report http://www.cbc.ca/news/canada/manitoba/story/2009/03/04/mb-light-bulbs.html
and the comments that it generated.

Much of the question in a cool place like BC comes down to the efficiency of producing heat with your boiler (about 85-95%) versus electrically.   If the electricity is produced hydroelectrically the efficiency is similar (about 80%), but no greenhouse emissions are produced.   However, if the electricity is produced by burning fossil fuels the efficiency is typically 40%, so you in net end up burning about twice as much fuel if you heat electrically versus with your own boiler or furnace.   One might argue that since BC produces a lot of electricity with hydro, electric heating is 80% efficient and produces no greenhouse gases.   It isn't that simple, because not all of BC electricity is produced with hydro and some electricity is sent to regions with fossil fuel electricity, so using electric heat will cause more fossil fuels to be consumed.

Using the 40% efficiency rate, the 60W light bulb gives about 15W of light and 45W of electric heat (the latter required about 100W worth of fossil fuels to be consumed) but only displaces 45W of fossil fuel in your how furnace.  Let's look at the total energy used by both bulbs.

• Incandescent uses 60W at 40% efficiency, so 150W of fossil fuels.
• CFL uses 15W (40W of fossil fuels at the electric plant) for light plus 50W (to make up the extra heating), totalling 90W, so the CFL uses about 40% less fossil fuel for the same amount of light and heat.  (Not the 75% that you get from comparing the wattages).

If you assumed that the electricity production is more than 90% efficient, the traditional light bulbs and CFLs are neck in neck.

• Incandescent uses 60W at 90% efficiency, so 67W of energy.
• CFL uses 15W (17W of energy at the electric plant) for light plus 50W (to make up the extra heating), totalling 67W, so the CFL uses about same amounts of energy for the same amount of light and heat.

If one argues that hydro-power is clean (and more power generation doesn't cause fossil fuels to be consumed) and we aren't worried about energy consumption but rather greenhouse gases, then the incandescent light comes on top.

This doesn't take into account how much energy it takes to make and dispose of a light bulb.  This complicates matters a bit because CFLs are costly but last a longer time and incandescents don't require much energy to produce but don't last as long.

However, all these arguments are turned on their head as soon as you turn off the heat and turn on the A/C or even crack a window.   In the first case the heat produced causes more energy to be consumed to move it outside, or in the second case it is simply lost to the environment.

I looks like CFLs make sense for BC and make even more sense in places with A/C, but if you live off of the grid and have a clean electric source (how about your own solar panels or hydro dam), then you can happily use incandescent bulbs and help the Earth because you won't have to use as much energy to heat your house.

Watching the Seasons Go By

A Bit on Snow on the Soil in the Backyard

A couple of days ago we had a little snow in Vancouver, so I
repeated the experiment of the New Year. I measured how far the snow line was from my fence. I got eight feet. That told me that the Sun was arctan(5/8) or 32 degrees above the horizon at noon. We are at latitude 49, so the Sun is now at 49 - (90 - 32) = -9 degrees, so the Sun is 9 degrees below the equator. We're getting closer to the beginning of spring when the Sun crosses over the equator just under one month from today.

Checking with Stellarium, the Sun is officially was a smidgen over 10 degrees south of the equator at noon yesterday, so once again our snowy sextant has down quite well.

How Many Blue Stars Can You See?

Looking out at the night sky you might notice that most of the bright stars are blue or blue-white and relatively few are yellow like the Sun.  Part of this is because it is difficult to sense colour from faint objects but also most of the bright stars in the night sky are main-sequence stars (fusing hydrogen to helium in their cores) more massive than the Sun; therefore, they appear bluer. The most massive stars are inherently brighter so we can see them over a larger volume.   Their power increases as M⁴ so the volume increases as M⁶ so if there were the same density of ten-solar-mass stars as one-solar-mass stars you would see a million times more ten-solar-mass stars in the night sky than one-solar-mass stars.  The ratio is not this dramatic which tells us that massive stars are rare.

Massive stars don't live as long as solar-mass stars, in fact the lifetime goes as mass over power, so M^-3.  If you include this lifetime effect and assumed that the birthrate of ten-solar-mass stars equalled those of one-solar-mass stars then the density of ten-solar-mass stars would be a thousandth of that of one-solar-mass stars.   In this case the ratio of the number of ten-solar-mass stars to one-solar-mass stars visible in the night sky would be 1000 to 1.   In fact the ratio is not this dramatic, so the birthrate of stars must not be constant with mass.   Among the ten brightest main-sequence stars in the night sky, only one α Centauri is about the mass of the Sun.

This lets us know that the birthrate must decrease with mass. If it decreased as
M^-3 or more steeply with mass, the sky would not be dominated by stars more massive than the sky. If it decreases as M^-2, there would be ten times more ten-solar-mass stars in the sky, that solar-mass stars. In fact most are less than ten-solar masses and greater than one-solar mass, this tells us that the birthrate or initial mass function must decrease somewhere in between these two extremes. In fact the best guess is from more careful analysis is around M^-2.35.

The Sun - Frosty Grass

My Backyard at the End of the Day

This is a great experiment that you can take advantage of a really cold day in Vancouver.  At the end of the day there will still be frost on the grass where the Sun didn't managed to reach throughout the day.  Because my back fence runs from east to west, this line of frost marks the highest point that the Sun reached in the sky during the day.  My back fence is five feet tall and the frost line lies fifteen feet from the fence, meaning that the Sun reached an altitude of arctan(5/15) or 18 degrees during that day.

This means that the declination of the Sun was 49-(90-18) = -23 around the end of 2010 which is about right.   It's amazing what you can figure out with a bit of frost.