Human Orrery

**Figure:** Children from the Armstrong Primary School, Armagh, at the Launch of the Human Orrery on 26 November 2004. The innovative `Dance of the Planets' was choreographed by dance teacher Jennifer Rooney. Upper image by Miruna Popescu, lower image by Julie Thompson (Armagh Planetarium).

The Armagh Observatory Human Orrery is believed to be the first large outdoor exhibit designed to show with precision the elliptical orbits and changing relative positions of the planets and other solar system bodies versus time. It is also the first major addition to the Observatory Grounds and Astropark for more than a decade, providing a dynamic map of the positions and orbits of the six classical planets, an asteroid and two comets, as well as an indication of the thirteen zodiacal constellations through which the Sun passes in the course of a year and pointers to more distant objects in the Universe.

The exhibit (see http://star.arm.ac.uk/orrery/) was constructed during 2004, with the support of the DCAL, close to the south-east corner of the main Grade A Listed Building, between the existing Library and two telescope domes. In general, it can be used to show the orbital periods of objects revolving around the Sun and also to illustrate a wide range of celestial phenomena, such as planetary alignments, conjunctions, transits, and the laws of orbital mechanics.

In the Human Orrery people play the role of the moving planets, and the scale model provides an accurate map of the orbits of the six classical planets, an asteroid and two comets, and shows their positions at any time. Users gain a better understanding of the principal parts of the solar system (Sun, terrestrial planets, outer planets, asteroid belt and comets) through a variety of games and activities, and are immediately faced with the elliptical orbits of the various objects and their different speeds around the Sun, as well as their differing directions in space as seen from the Earth, the Sun, or any other point in the model.

The Human Orrery thus facilitates activities such as establishing Kepler's laws by direct measurement, and the introduction of concepts such as planetary alignments, conjunctions and transits. In particular, because questions of distance-scales, time-scales, and the dynamics and spatial relationship between solar system bodies lead naturally to questions concerning the calendar, the seasons, the equation of time, and the precession of the equinoxes, the Human Orrery can also be used to introduce ideas such as leap years and the need for the Gregorian calendrical reform.

The Orrery was formally opened on the morning of the day of the Robinson Lecture, around midday on 26 November 2004, in the presence of approximately 40 external guests, as well as Armagh Observatory staff, students and associates. An innovative `Dance of the Planets' (see Figure 16), facilitated by Dance Northern Ireland, was choreographed by Ms Jennifer Rooney and performed by twenty-five P7 pupils from the local Armstrong Primary School, watched by guests including parents from the school.

When the Human Orrery is finally completed in 2005, it will also show the thirteen zodiacal constellations through which the Sun passes in the course of a year and the directions to a wide range of more distant objects in the Universe. The idea is to explain the Earth's position in space at a variety of different levels, and to link this understanding to direct observations of the Sun, planets and stars. In this way, the Human Orrery provides a wealth of educational and public outreach opportunities, ranging from the level of primary school children up to adults and university students.