What sort of telescope is best for observing double stars?

BBC Sky at Night Magazine's Scope Doctor Steve Richards solves your astronomy ailments.

A good way of testing and enhancing the keenness of your eyes is by observing double stars. Credit: Ninian Boyle

I like viewing double stars. I currently have a 6-inch reflector but would a refractor work best? What would you recommend for a budget of £300?

Steve says: “Observing double stars is a very popular aspect of astronomy and an area where amateurs can contribute greatly as very few professional observatories make such observations these days.

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Observational data is vital for increasing our understanding of stellar evolution, so amateurs can carry out real science as well as enjoying the wonderful sights.

A 6-inch reflector will produce some great views of double stars but a good refractor is likely to give a better observing experience as there is no spider vane to create diffraction spikes, which can cause issues with very close doubles.

A long focal length refractor will give excellent views and make focus easier to achieve, but this needs to be combined with as large an aperture as you can afford.

Larger apertures will reveal fainter companions but, just as importantly, they will have a higher resolution allowing you to split closer doubles.

Long focal length refractors require a substantial mount to counter the effects of wind shear in particular.

Unfortunately, large aperture refractors can be quite costly, so a very popular, lower-cost alternative instrument for double star observing is the 5-inch Maksutov-Cassegrain.

This instrument has a wide aperture and a long focal length of around 1,500mm in a short physical length and would be an excellent choice within your budget.

The Sky-Watcher Skymax-127 Maksutov- Cassegrain or Orion Apex 5-inch Maksutov-Cassegrain telescopes would be excellent choices.”

Some other useful guides that might help:

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Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.