With all this white stuff falling from the sky and blanketing the ground, and the moon and Venus shining so brightly in the sky, I’m reminded of an interesting concept I learned about in graduate school: albedo. Astronomers use the term albedo to quantify how much visible light a surface or object diffusely reflects.

Consider snow, for example — plenty of that around to illustrate the point. The albedo of freshly fallen snow is very nearly 1, meaning that a surface of fresh snow reflects nearly 100% of the visible light that falls on it.

Note that a smooth, snowy surface reflects light differently than, for example, a nice clean mirror. A snowy surface on a sunny day reflects incident light rays every which way, making the surface appear bright no matter how you look at it. A mirror reflects incident light rays so that each ray goes out at the same angle, relative to the mirror’s surface, as it went in. The term albedo is usually used to quantify diffuse reflection (or scattering) off a relatively rough surface, like a snow hill or a dirt road, rather than what’s called specular reflection off a smooth, shiny surface, like a mirror.

The albedo of snow is among the highest of all naturally occurring materials; snow is very white and bright, even on a mostly cloudy day. And speaking of clouds, when illuminated by the sun, they are very bright too.

It’s interesting, but off topic, to wonder why clouds and snow — both composed of water, which is transparent to visible light — have such a high albedo. And why the foamy head on a nicely drawn mug of beer is bright white, when the beer itself is yellowish and transparent. That’s for another column.

Astronomers have long measured the albedo of solar system objects to learn what the planets might be made of. If you’ve seen Venus lately, you won’t be surprised to learn that Venus has the highest albedo of any planet in the solar system. Venus reflects between 60% and 70% of the sunlight that falls on it. You might also be surprised, given the recent famously bright full moons, to hear that the moon’s albedo is very low. The moon reflects only about 10% of the sunlight that falls on it.

Imagine if the moon’s albedo was as high as Venus’. A full-moon night here on earth would be six times brighter.

We can also consider what earth must look like from other planets. Earth’s albedo is about 0.35, about half way between that of the moon and Venus. Viewed from Venus, the earth, which is about the same size as Venus, would appear only half as bright as Venus does from earth.

What’s Venus got that earth doesn’t? Earth is one-third covered by dark landmasses and two-thirds covered by water. And although the albedo of water can be very high, like when water is in the form of tiny droplets or frozen flakes of snow, the albedo of liquid water — of the oceans — is in fact very low. Liquid water is mostly transparent, so sunlight goes right into the oceans and is eventually absorbed. In fact, if it weren’t for the clouds that always partially cover earth’s surface, earth’s albedo would be much lower than it actually is.

Venus is totally cloud covered, and that’s why its albedo is so high, and why it is now so bright in the evening sky.

This column originally appeared in the Grand Haven Tribune on 16 January 2009.

In the news are reports that the December 2008 full moon was the biggest and brightest of the year. True enough. The moon’s orbit isn’t perfectly circular, so the moon is sometimes a bit closer to the earth and sometimes a bit further away. December’s full the moon was as close to the earth as it gets. The result: a big, bright full moon.

Coincidentally, I caught a glimpse of the moon — one of the most unusual nearly-full moon’s I’ve ever seen — Thursday morning, Dec. 11, while walking the dog along the lakeshore. I wish I had camera with me; I’m at a loss to describe it with words.

Strolling along Harbor Drive in the wind and cold before sunrise, I happened to see a long, thin red glow out in the lake. At first I thought it was a ship, but the color wasn’t right. As the minutes ticked by, I realized I was looking at the moon slipping out from behind the clouds through what must have been a narrow swath of clear sky at the horizon toward the northwest. As I made my way north, the big, red moon, misshapen by refraction in the thick atmosphere, set gently on top of the lighthouse.

And after seeing the sight, I was reminded of an experiment I conducted, or rather tried to conduct, as you’ll learn, some years ago when I was unencumbered by having a regular job.

The holiday season is a busy time of year. Have you ever wished there were more hours in a day to get things done? Sometimes just an extra hour would be so helpful.

The sun defines our sometimes-too-short twenty-four hour day. The sun rises, passes overhead, sets and rises again once every twenty-four hours, and we march to the beat of its drum.

The moon, however, drums a different beat. The moon rises and sets about fifty minutes later each day compared to the day before. This delay, a consequence of the fact that the moon makes its way around the earth once each month. A day by the moon is nearly twenty-five hours long — there’s that extra hour!

So one day in Y2K, I decided I would try to live on moon time. I would get up around moonrise and go to bed around moonset, following the moon around the month, living luxurious twenty-five-hour-long days.

I started to march with the moon one day when the moon was new. The new moon rises and sets with the sun. Then each day I stayed up an extra hour or so and tried to sleep in an extra hour.

I was encouraged that I could adapt to the moon’s slow swing-shift by something I read about our natural sleep-wake cycle. It seems that physiological cycles combine with environmental signals, like the onset of darkness, to send us to bed at the end of each day. Absent the environmental clues — like when a sleep-research subject is asked to live in a cave for several months — it turns out our natural sleep-wake cycle runs more like twenty-five hours long. A moon day!

But I learned that the environmental clues are very powerful. After about ten days, when I was supposed to stay up to 7 am and sleep in until 3 pm, I was a zombie. I switched back to sun time and gave up the quest to put an extra hour in my day.

I’m interested to hear if anyone else has ever tried this.

This column originally appeared in the Grand Haven Tribune on 12 December 2008.

Scientists at the U.S. Geologic Survey (USGS) pinpointed the source of the tremors that were felt across the Midwest last Friday.

“The April 18 earthquake is located within the Illinois basin-Ozark dome region, which covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis. Moderately damaging earthquakes have historically occurred at irregular intervals in this region, ….,” according to the USGS National Earthquake Information Center.

The location of the 18 April 2008 earthquake felt across the Midwest. Map courtesy the USGS.

The earthquake experts place the quake seven miles below a point on earth’s surface near the small town of Bellmont, IL. A tremendous amount of information about this event is available online at http://earthquake.usgs.gov.

Just three days after the quake, the USGS released an updated national seismic hazard map. This map shows that earthquakes may occur just about anywhere in the U.S. (and around the world), but fortunately for us here in West MI, a significant shaker is highly unlikely to strike close to home.

2008 update of the US seismic hazard map produced by the USGS.

Data that scientists use to pinpoint earthquakes and estimate their hazards come from sensitive vibration-measuring instruments called seismometers. If data recorded by a seismometer during an earthquake is played back fast (like playing a 33 at 45 — OK, only some of know what that means) they sound like sounds. Click this sentence for a sample.

More samples of earth’s seismic sounds are available at http://earthquake.usgs.gov/learning/listen/.

Earth is a dense, rocky place that crunches and grinds as it ages and settles. The sounds it makes are much like you might imagine, sort of crunchy and grindy — not really music to anyone’s ears.

But another solar system body sings in much more beautiful notes: the sun. Because the sun is not solid it vibrates and rings much more freely than does earth.

Scientists study the sun in extraordinary detail. One of the main instruments used to study the sun is the Solar and Heliospheric Observatory, or SOHO for short. SOHO is a satellite built and managed by a host of universities and research centers around the world, including NASA and the European Space Agency. One of the things that SOHO observes about the sun is the way it vibrates.

“The outermost quarter of the Sun’s interior is a constantly churning maelstrom of hot gas. Turbulence in this region causes ripples that criss-cross the solar surface, making it heave up and down in a patchwork pattern of peaks and troughs,” according to a recent mission summary on the SOHO website http://sohowww.nascom.nasa.gov.

A computer-generated representation of the vibrating sun from an introduction to helioseismology at http://soi.stanford.edu/results/heliowhat.html.

An MPEG video clip of ripples on the seething surface of the sun is available at http://soi.stanford.edu/press/agu05-98/flare.mpg.

SOHO measures the sun’s vibrations with a device called the MDI (short for something much longer), which is something like a solar seismometer. The MDI is a project of the Stanford-Lockheed Institute for Space Research. Like earthquake data, if MDI data are sped up and played back, they also sound like sounds. Click this sentence for a sample.

More sun sounds are available at http://solar-center.stanford.edu/singing/.

The sounds of the sun are sometimes peaceful and pleasant, like a meditation gong, yet sometimes a bit rough. The rough sounds are those of sunquakes — powerful waves that ripple around the sun from time to time — caused by solar flares.

So there are earthquakes on earth and sunquakes on the sun. Because things are better in threes I’ll note that seismometers left on the moon by the Apollo astronauts confirmed that there are also moonquakes on the moon.

Buzz Aldrin (Apollo 11) deploys a seismometer in the Sea of Tranquillity. Image courtesy NASA.

Look for a new post on or about 4 May 2008.