In March 1998 we were told that a huge asteroid would hit the Earth. Did it change course?

Asteroids don’t “change course” in the sense that they suddenly disobey the laws of physics and veer away. Astronomers get more data as a result of which they find that their previous calculations were wrong to predict an encounter (or, uncharitably, better astronomers/mathematicians get to grips with the orbital data and make better predictions from the same data).

Michael Forrest, Henley-on-Thames, Oxon

Why are products made of Bakelite so often dark brown in colour?

Bakelite is the trade name for a group of products based on phenol/formaldehyde resin. This resin is naturally dark. The filler in cheap products was wood flour which discolours in the moulding process. Other similar products have used bleached cotton (paxolin) and these laminates are straw coloured. Later urea/formaldehyde resins were invented. These resins are water white and give rise to products that can be made in bright colours.

J. Hartley, Walton on Thames, Surrey

Why does screwing up one’s eyes make pixellated images clearer?

Our sight has evolved to cope with natural distortions owing to poor light, rapid movement, tears in our eyes, etc. Pixellated images are not natural and they confuse our minds. Blurring the pixellated images slightly makes them appear unfocused but more natural.

Roy Hyde, Cheltenham, Glos

Why are crude oils containing high and low levels of sulphur termed “sour” and “sweet” respectively?

High sulphur crude oils usually contain part of the sulphur in the form of hydrogen sulphide and mercaptans, both of which smell sour. Hydrogen sulphide has the smell of rotten eggs and even if this is removed by processing in the oilfield there remains the objectionable smell of mercaptans.

Gordon L. Clark, Tunbridge Wells, Kent