Recent work by MacDonald et al. has highlighted the valuable work carried out by sky watchers and auroral enthusiasts in obtaining high-quality digital images of rare and unusual auroral structures. A feature of particular interest, which has been nicknamed Steve, typically takes the form of a short-lived arch, beam, or narrow band of light in the sky. MacDonald et al. have established that the phenomenon is characterised by a range of optically visible low magnetic latitude structures associated with a strong subauroral ion drift. Respecting its nickname, they have dubbed the phenomenon STEVE, an acronym for Strong Thermal Emission Velocity Enhancement. Here, we draw attention to earlier observations of similar structures, showing that some previously unidentified atmospheric, meteoric or auroral anomalies can now be recognized as examples of Steve, and therefore as part of a broad spectrum of occasional auroral features that may appear well below the region of magnetic latitudes represented by the traditional auroral oval. This highlights the contributions of citizen scientists dating back hundreds of years, and the importance of reassessing historical reports of rare auroral luminosities for a full understanding of the range of solar activity over millennia.

This chapter provides a review of the asteroid and cometary populations of the Solar System. It begins by reviewing the growth in our knowledge of the near Earth objects (NEO) population, basic observational properties such as their size distribution and astrophysical theories for their origin. It considers the history of the bombardment of the Earth by comets and asteroids, the effects of impacts by bodies of different sizes and the risk they pose at present. The latter is interpreted in the context of other low-frequency/high-impact risks, together with an insurance or actuarial approach to evaluating the average annual cost of NEO impacts and possible approaches to mitigation. Finally, their long-term implications and the perspective they provide on our place in space are discussed.

Assessments of the risk posed by near-Earth objects ignore the possibility of a giant comet entering the inner solar system. Bill Napier, David Asher, Mark Bailey and Duncan Steel examine the likelihood and potential consequences of the appearance of such a centaur.

The learning process is often enhanced by active participation (e.g., [1]). Combining this idea with the concept of an orrery – a mechanical model of the planetary system – leads us to the possibility of a Human Orrery, in which users play the role of the planets. Such an exhibit has been constructed at the Armagh Observatory in Northern Ireland (Fig. 1) and has been used to explain principles of planetary motion to the general public [2]. The Human Orrery has proved successful and another version, using the same template, is now (2009) being built at the Kings School, Peterborough in England.

We review the history of the prediction of, and searches for, a population of comets and transneptunian planetesimals. Starting with initial speculations before and after the discovery of Pluto, we examine various predictions by Edgeworth, Kuiper, and others on the existence of such a population and review the increasingly sophisticated theoretical efforts that eventually showed that the number of short-period comets requires that an ecliptic transneptunian popu- lation exists. We then recount various search programs that culminated in the discovery of the first few transneptunian objects and led to the realization that this region is dynamically much more complicated than first suspected and has important links both to Centaurs and the dense inner core of the Oort cloud.

The Lindsay Centennial Symposium celebrates the wider importance of astronomy in Ireland and its unique role in advancing our understanding of the world in which we all live. Astronomy is an international endeavour that transcends political boundaries and helps to draw people together. Virtually every country in the world-and Ireland is no exception-looks to astronomy as part of its national heritage and as an activity, in common with other nations, that goes back almost to the dawn of civilization. In Ireland, astronomy can be traced back more than five thousand years to the time of the construction of megalithic monuments, such as the famous passage-tomb at Newgrange. More recently, Ireland was home to the largest optical telescope in the world, the so-called 'Leviathan of Parsonstown'. Lindsay played a major role in advancing Irish astronomy. He recognized, very early on, that astronomy is not merely a national activity, but an international one as well, and one that on the island of Ireland must include close collaboration between the two jurisdictions: Northern Ireland and the Republic of Ireland. Astronomy attracts people, young and old, into science and to a more scientific way of thinking; it addresses issues of major significance for culture and for our understanding of mankind's place in the Universe; and provides young people with challenges in science and mathematics that are of the utmost technical difficulty and which bring important practical benefits to society. The occasion of the 100th anniversary of Lindsay's birth is a time of great optimism for political and economic developments on the island of Ireland, and especially for the growth of astronomy on both sides of the Border and as part of Ireland's involvement in wider European science.

These days everyone is taught the principles of the Earth’s place in the Universe: that our planet is one of nine traditional planets orbiting the Sun in the solar system; that its nearly circular orbit lies in a plane (the ‘ecliptic’) that reflects the path of the Sun in the sky; that the orbits of the other planets lie very close to the same plane; and that the Earth takes a year of 365.25 days to revolve once about the Sun. Contrast this with the results of casual observation: a planet that is very much at rest; stars and the Sun that appear to circle the Earth every day; and five classical planets that either stay close to the Sun in the sky (as with Mercury and Venus), or move slowly from west to east against the fixed stars, repeating their positions at intervals of several years or more. The difficulty facing modern educators — one which resonates with one of the biggest paradigm shifts in science — may be described as the ‘geocentric illusion’. Indeed, if one abandons the call to a higher authority or arguments by assertion, the points in question are among the hardest to explain in a simple way. As a result, there are many people, perhaps some among this audience, who really have no idea of the Earth’s position and the positions of the other planets in 3-dimensional space. The general problem can be illustrated by asking two very simple questions: (1) ‘how far can you see on a clear day?’; and (2) ‘why do January mornings, as now, remain dark for so long after the winter solstice?’. The answers depend on understanding the Earth’s position and orientation in space and knowing a bit about its elliptical orbit around the Sun. Of course, a moment’s thought will soon convince you that the Sun is the farthest object normally visible on a clear day, but people often argue whether the correct answer is a few miles — or even a few hundred miles — i.e. to most distant horizontal horizon. In turn, this is a lower limit to the radius of the celestial sphere. Similarly, the correct answer to the second question initially eludes most people, but once they start thinking they soon recall knowledge learned, but not understood, at school. In fact, most of us are natural Aristotelians, and we intuitively think of a geocentric model of the Universe, where the Earth is at rest and where the Sun, planets and other solar system objects move slowly against the fixed backdrop of a more distant ‘celestial sphere’. An orrery, which is a dynamic model of the solar system, is designed to help us avoid this mistake, and to explain, in an informative and entertaining way, the heliocentric solar system. The earliest such model was invented by the English clock-maker and inventor, George Graham (c.1674–1751), around (or soon after) 1700. Graham gave a copy of his first model, or its design, to the celebrated London instrument maker John Rowley (1674–1728), later Master of Mechanics to George I. Rowley then made a copy for Prince Eugène of Savoy, and another for his patron, Charles Boyle, the fourth Earl of Cork and Orrery (1674–1731), which he presented around 1712 to Boyle’s first son, John (1706/1707–1762), later the fifth Earl of Cork and Orrery. In this way, the device to illustrate the heliocentric model of the solar system received the moniker ‘orrery’. The idea was an immediate success, and many variants of the original model were soon under construction.

Mark E Bailey reports from the Sixth European Dark-Skies Symposium, held in Portsmouth on 15 and 16 September 2006.More than 100 people including members of the British Astronomical Association Campaign for Dark Skies (CfDS), representatives from local and central government, lighting professionals, environmentalists, astronomers and journalists, met in Portsmouth for the Sixth European Dark-Skies...

The Armagh Observatory Human Orrery is the first major addition to the Observatory grounds and Astropark for more than a decade. This 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. The Human Orrery provides 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 13 zodiacal constellations through which the Sun passes in the course of a year, and pointers to more distant objects in the universe. This article describes the key features of its design and construction, and indicates how educators may use the exhibit as an innovative tool to communicate astronomy, mathematics and space science to people of all ages.

Mark E Bailey and Tom Ray give an overview of the National Astronomy Meeting in Dublin, where record numbers of astronomers went to talk, listen and network.

Duncan Steel and Mark Bailey report on the well-attended December 2001 G Discussion Meeting whose subject was near-Earth objects.

The majority of comets that reach the inner solar system originate in the Oort cloud. However, models describing the dynamical evolution of such comets predict far more comets in short-period orbits than are observed. In his Perspective, Bailey discusses the implications of a more refined model ( Levison et al.) that still predicts a surfeit of observed Halley-type comets relative to observations, and which concludes that the majority of Oort cloud comets disrupt into invisibly small fragments. This and other suggestions to account for the cometary missing mass are discussed. While important clues are being gathered, the coupled physicodynamical evolution of comets presents an intriguing puzzle.

Mark Bailey reports from South Africa on the ground-breaking ceremony for the Southern African Large Telescope on 1 September 2000.

Observations of massive, extended discs around both pre-main-sequence and main-sequence stellar systems indicate that protoplanetary discs larger than the observed planetary system are a common phenomenon, while the existence of large comets suggests that the total cometary mass is much greater than previous estimates. Both observations suggest that theories of the origin of the solar system are best approached from the perspective provided by theories of star formation, in particular that the protoplanetary disc may have extended up to ~103AU. A model with a surface density distribution similar to a minimum-mass solar nebula, but extending further in radius, is derived by considering the gravitational collapse of a uniform, slowly rotating molecular cloud. The boundary of the planetary system is determined not by lack of mass, as in previous ‘mass-limited’ models (i.e. those with a sharp decrease in surface density Σ beyond the radius of the observed planetary system), but instead by the increasing collision time between the comets or planetesimals initially formed by gravitational instability beyond the planetary zone. Bodies formed beyond ~50 AU have sizes on the order of 102km and represent a collisionally unevolved population; they are composed of relatively small, unaltered clumps of interstellar dust and ices with individual sizes estimated to range up to ~10 m. By contrast, bodies formed closer in, for example in the Uranus-Neptune zone, consist of larger agglomerations of dust and ices with individual sizes ranging up to ~1 km. Planetesimals formed by gravitational instability at smaller heliocentric distancesrare typically much smaller than those formed further out, the massesmpbeing proportional to Σ3r6, but subsequent collisional aggregation in the planetary region is expected to produce bodies with sizes ranging up to 102km or more. In both cases the first-formed solid objects may be identified with observed cometary nuclei; some accumulate to produce the outer planets, but the majority are ejected, either to interstellar space or into the Oort cloud. Observed comets represent a dynamically well-mixed group from various sources; they are expected to comprise a heterogeneous mix of both pristine and relatively altered material and to have a broad mass distribution ranging up to the size of the largest planetesimals.