Science: Technoquest

Q The Moon orbits the Earth every month. Why then isn't there a solar eclipse (where the Moon blocks out the Sun) every month?

The Moon's orbit is tilted in relation to that of the Earth around the Sun by 5.2 degrees. The lunar orbit does not oscillate, so the moon's orbital plane does not rotate as the Earth rotates around the Sun. This means that an eclipse only occurs if the alignment of Moon, Sun and Earth is exactly right.

Q What uses does the Aspilia plant have?

The genus Aspilia, a member of the Compositae (Daisy) family, is certainly interesting: it has representatives from tropical America through to Africa and Madagascar. The total number of species recognised in the last revision was around 60. It finds uses in solving many medical problems including eclampsia, lumbago, sciatica, neuralgia and malaria. It also has antibacterial and antiparasitic properties. This is not to say that every species will have one or more of these uses, or that the usage is proven as effective, but it is certainly a good indication of the potential bioactivity of members of the genus.

One fascinating aspect about members of this genus is the way that primates, particularly chimpanzees, also appear to use them for their medicinal activity; indeed it would seem that man has learned such uses from them.

Q Did England once have different time zones within it, as the United States now does?

Not officially. However, before modern communications systems, when there was no way of telling people around the country what the exact time was, people relied on their local sunrise and sunset to set their clocks. As the sun rises and sets at different times across the country, this meant a difference in times between towns. The arrival of trains, and timetables, enforced unification around a common time.

Q Where is the temperature probe to measure the outside temperature located on a car, and why is it not affected by wind chill and/or engine temperature?

The probe is under the front bumper, protected from wind chill (which only really affects humans anyway), and far enough away that its readings are not affected by the engine's temperature.

Q Is it possible that a planet could orbit the double star system Sirius A and B?

Sirius A is an a type A1 star, with 27 times the Sun's luminosity, while Sirius B is a white dwarf with only 0.02 times the Sun's luminosity. You can consider Sirius B as being in a very elliptical orbit around Sirius A (actually, they both orbit their common centre of mass) with the distance between them varying from about 7 to 28 AU - where 1 AU is defined as the distance between Earth and Sun. As it happens, Jupiter lies about 7 AU away from the Sun, and Neptune about 28 AU away.

Current theories suggest that planets are very unlikely to form in a close binary star system: the companion star (in this case Sirius B) would tend to throw the "building blocks" for the planets out of the entire system, disrupting their formation. Theory also suggests that only stars whose mass is less than 1.5 times that of the Sun will have orbiting planets; Sirius A's mass is 2.3 times greater than the Sun's.

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