The Great Lakes, unfrozen

The NASA image above (click to zoom) shows the Great Lakes in Autumn 2011. The image is again from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite. Lake Michigan and Lake Huron are coloured light blue from sediment brought to the surface by winds, while Lake Erie is coloured green by a severe algal bloom. Autumn colours are also visible in some of the forests surrounding the lakes.

Given that it’s autumn here in Australia right now, the image seems vaguely appropriate.

Mars gets closer and brighter…

On April 8, the planet Mars was in opposition. That is, Mars was on the opposite side of the sky to the Sun. Also, on April 14, Mars will be at the closest point to Earth in its orbit (92 million km). A great time to observe the “red planet”!

This video from Slooh explains various aspects of the planet at length:

For the current distance to Mars, see Wolfram’s calculator or the live diagram of the solar system at Fourmilab, which includes images (green lines show orbits below the plane of the ecliptic):

Live Solar System image

The Heartbleed bug

Just a reminder of the Heartbleed bug, which potentially compromises sensitive user data on affected systems. This means some passwords need to be changed now; others later. Some sites, such as LinkedIn and eBay, were apparently not affected.

A number of organisations, such as online banks, have produced somewhat confusing responses to the problem. In general, if your bank claims to have “patched” the problem, you should probably change your password, even if they say not to.

Update: Count on XKCD to see the lighter side of the problem – data stored on clay tablets is perfectly safe:

XKCD also has a good explanation of what the actual problem is.

Accurate to one second in 300 million years

The US National Institute of Standards and Technology has announced a new caesium-based atomic clock, NIST-F2 (see photo above). The clock is accurate to one second in 300 million years. Together with the older NIST-F1 clock, it will serve as the US civilian time standard – underlying time services such as the one at The diagram below gives a conceptual view of how network time servers interconnect. Accurate clocks like NIST-F1 and NIST-F2 underpin the whole enterprise.

See also this story in Wired.

Kitchen chemistry: soap

Our previous kitchen chemistry post discussed fats and oils, which are “triple esters” of glycerol:

Apart from their role in diet, fats are also used to produce soap:


The soap-making process involves reacting fats with strongly alkaline substances, such as lye (sodium hydroxide, NaOH). This can be done at home, but since lye is dangerous, soap-making is not appropriate for children (see these precautions: 1, 2, 3).

In solution, the lye exists as sodium (Na+) and hydroxide (OH) ions (indeed, the presence of hydroxide ions is what “alkaline” means). The hydroxide ions react with the fat to free the glycerol:

Saponification reaction

Fatty acid ions (such as stearate ions, C17H35COO) are also produced:

Since the sodium ions from the lye still exist, soap is basically sodium stearate, sodium palmitate, or something similar. Because it is the result of reacting a very strongly alkaline substance (sodium hydroxide) with very weak acids (fatty acids), soap itself is also alkaline. This alkaline nature can be harsh on the skin, and especially on the hair. Shampoos are therefore usually made from synthetic detergents, and formulated to be mildly acidic (with a pH between 5 and 7).

Another problem with soap is that it reacts with dissolved calcium, iron, or magnesium ions in hard water, giving an insoluble soap scum of compounds such as magnesium stearate. This can be demonstrated at home by mixing soap solution with a solution of epsom salts (see here or here).

The Great Lakes by night

The image above is cropped from a beautiful NASA image of North America by night, assembled from satellite photos taken by Suomi NPP during 2012. Population centres are clearly visible (click for image without labels). The great lakes themselves also stand out distinctly, even against the thinly populated regions.