page_title: Burt's solar compass
section_title: Description
hierarchical_section_title: Burt's solar compass / Description
caption_attribution_description: English: Line illustration of Burt's solar compass from his 136 US Patent showing the components assembled and suitable for explaining the function of the instrument
context_page_description: Burt's solar compass or astronomical compass is a surveying instrument that makes use of the sun's direction instead of magnetism. William Austin Burt invented his solar compass in 1835. The solar compass works on the principle that the direction to the sun at a specified time can be calculated if the position of the observer on the surface of the Earth is known, to a similar precision. The direction can be described in terms of the angle of the sun relative to the axis of rotation of the planet.
  This angle is made up of the angle due to latitude, combined with the angle due to the season, and the angle due to the time of day. These angles are set on the compass for a chosen time of day, the compass base is set up level using the spirit levels provided, and then the sights are aligned with the sun at the specified time, so the image of the sun is projected onto the cross grating target. At this point the compass base will be aligned true north–south. It is then locked in place in this alignment, after which the sighting arms can be rotated to align with any landmark or beacon, and the direction can be read off the verniers as an angle relative to true north.
caption: Line illustration of his solar compass
  from 1836 US patent documentation.
exif: {}