page_title: Rasmus Sørnes
section_title: The "Clock No. 3"
hierarchical_section_title: Rasmus Sørnes / Clockmaking / The "Clock No. 3"
caption_attribution_description: English: Second Astronomical clock designed by Rasmus Sørnes
context_page_description: Rasmus Jonassen Sørnes, was a Norwegian inventor, clockmaker and radio technician, and is most famous for his advanced astronomical clocks, the most precise of which has an inaccuracy of 7 seconds during 1000 years. During his lifetime, Sørnes also designed and built a large variety of agricultural, radio-technical and mechanical devices, only a few of them patented.
context_section_description: Rasmus Sørnes steadily kept improving his design and adding even more features, and in 1954, the 3rd clock was finished.
  The gear trains from the two previous clocks have been revised for improved accuracy, several correction works have been added to make up for irregularities in the celestial orbits, and most importantly, the precession of the equinoxes has been taken into account.
  The base of the clock contains a tape recorder, with recordings of Rasmus Sørnes' voice describing the features of the clock. The clock's astronomical part may be driven forwards and backwards at a speed of eight days per minute. The large dial in the middle of the front has a fixed Zodiac and two hands showing the position of the Sun and the Moon on the ecliptic circle. The Sun hand makes one revolution every year, and the Moon hand one revolution every 29.5 day. This dial also shows when and where solar and lunar eclipses occur. The orbit of the Moon has an inclination of 5° with regard to the ecliptic, so solar or lunar eclipses can only occur when the Sun and the Moon are simultaneously located at one of the crossings of the two orbits. These two crossings rotate once in 18.5 years (known as the Saros cycle) and are indicated by the hand with the Ω (omega) sign. Eclipses occur when the three hands overlap, which typically happens two or three times a year; they overlap in nearly exactly the same position every 18.5 years. In the centre of the dial, a spherical slice of the Earth is located. It rotates counter-clockwise once in a sidereal day, and is used to indicate where the eclipse is visible.
  At the bottom of the clock, two globes are located. The terrestrial globe rotates once per day, and the arc shows the division between day and night. The celestial globe shows the stars as they would appear if projected on a sphere surrounding the Earth. It rotates once in a sidereal day, but it also rotates around a second axis once in 25,800 years because of the precession of the equinoxes. To achieve this, a gear train with a ratio of 1:9,500,000 is required. This globe is illuminated from inside, and holes are drilled for the larger stars.
  This clock is on display at Borgarsyssel Museum, Sarpsborg, Norway. However, during 2013 it was stored away while the building was being renovated.
caption: Clock No. 3
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