2020 events

Sun 11:00-11:30
Venue: 
Starlight Room

Using Gravity to Find Stars

Peter Osman

Sydney City Skywatchers

Very few ultraportable equatorial telescopes come with digital setting circles. This talk describes a PushTo equatorial telescope with digital differential setting circles that can be readily assembled using simple hand tools. The complete system is designed for basic spectrophotometry and spectroscopy and can fit in an instrument case and a tripod bag.

The setting circles use accelerometers referenced to the earths gravitational vector rather than stars, so that star pointer alignment need only be done once in daylight hours. During daylight at the dark site the telescope just needs to be levelled and the polar altitude checked against latitude using the accelerometers. Polar alignment after sunset takes about ten minutes using drift polar alignment to find true south. In operation a single reference star is selected for each target it then takes about two minutes to point a ‘push to’ telescope within two to five arcminutes of the target.

The Research Centre for Astronomy and Earth Sciences in Budapest first reported the use of accelerometers for setting circles. The work described here has developed a more stable hour angle equation for use with small telescopes together with transformations that allow differential operation for star hopping. A mobile phone App has been developed to manage the PushTo database and operation. It is hoped this system will be useful for those who wish to recycle telescopes mounts without having to modify them; and for city dwellers living in small units who wish to travel to dark sites using public transport.