
David W. HughesThe University of Sheffield | Sheffield · Department of Physics and Astronomy
David W. Hughes
Doctor of Philosophy
About
356
Publications
23,482
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
3,744
Citations
Publications
Publications (356)
The previous Transits of Venus Working Group report #6, covering the
time mid-2006 to mid-2009, was published by the undersigned in the
Journal of Astronomical History and Heritage, Vol. 12, p. 254 (2009).
The present report #7, covering the time up to mid-2011, has been
prepared for the Reports presented at the IAU General Assembly in
Beijing, Aug...
The numbered Jupiter family comets (orbital periods P < 20 yr) have a median orbital inclination of about . In this paper, we integrate the orbits of these comets into the future, under the influence of both typical non-gravitational
forces and planetary perturbation, using a Bulirsch–Stoer integrator. In the case where non-gravitational forces wer...
Astronomy was revolutionized in the 20th century. The electron was discovered in 1897 and this transformed spectroscopy and introduced plasma and magnetohydrodynamic physics and astro-chemistry. Einstein’s E = mc2, solved the problem of stellar energy generation and spawned the study of elemental nuclear synthesis. Large telescopes led to a boom in...
John Michell, M.A., B.D., F.R.S. (1724-1793), was the first scientist to apply statistics to the spatial distribution of the stars on the celestial sphere. He was the first to realise that certain groupings, like the Pleiades cluster in Taurus, were non-random, thus indicating that these stars were a physical group in space, held together by gravit...
The SMART-1 mission has recently arrived at the Moon. Its payload includes D-CIXS, a compact X-ray spectrometer. SMART-1 is a technology evaluation mission, and D-CIXS is the first of a new generation of planetary X-ray spectrometers. Novel technologies enable new capabilities for measuring the fluorescent yield of a planetary surface or atmosphere...
Since 1801 the multitude of bodies that orbit between Mars and Jupiter have been called planets, small planets, minor planets, petites planètes, kleine Planeten, planetoids and asteroids. We investigate the popularities of these nomenclatures and chart the way in which, over the last 20 to 30 years, the use of Sir William Herschel's word `asteroid'...
D-CIXS initial observations show a first unambiguous remote sensing of calcium in the lunar regolith. Data obtained are broadly consistent with current understanding of mare and highland composition. Ground truth is provided by the returned Apollo and Luna sample sets.
The absolute magnitude of a star, this being the apparent magnitude that a star would have if it was moved to a distance of 10 parsecs from the observer, is a ubiquitous concept and is commonly used by today's astronomers to represent the luminosity of a star. This short paper traces the history of the expression 'absolute magnitude' from the time...
The rate at which the surface of Earth is being cratered can be measured by analyzing the sizes and ages of the craters that are found on certain stable areas of the Earth's landmass. It is shown, over the range 2.5 < D < 100 km, that the number N(D) of craters that are formed per unit area per unit time larger than diameter D does not (as previous...
Comet Halley's timely approach to the Sun in 1986 was an opportunity that European astronomers grasped with both hands - and
reaped the rewards, in the form of the first close images and measurements of a comet's nucleus. This noted success came about
to a large extent because of the right people in the right places in ESA, around 30 years ago. A c...
On a typical astronomical day we can gaze at the solar disc and see a 5,776 K gas radiating into space. Come night-time we are confronted with a panoply of stars with surface temperatures between 2,750 and 45,000 K, and maybe our Moon with a sub-solar-point temperature of around 410 K, and planets Jupiter and Saturn with cloud temperatures of aroun...
This paper concentrates on the relationship between the rate of gas emission from the nucleus of Comet 9P/Tempel 1, the fraction f of the nucleus that is active, and the crater damage inflicted by the recent 2005 July 4 Deep Impact space mission. The cometary nucleus has a surface area of about 1.7 × 108 m2 and a mean radius of about 3700 m. Before...
In the early 17th century it was generally accepted that the size of a
planet was related to its distance from the Sun. The Lancashire
astronomer Jeremiah Horrocks (1619-42) took this a stage further. For
the planets known at the time he suggested that the planet-Sun distance
was about 15 000 times the planetary radius. This was equivalent to
sayin...
"It is a poor workman who blames his tools" - but that said, a stellar astronomer can only work with the material and the tools that have been provided. When it comes to the early history of stellar astronomy the "tool" was the naked eye and the "material" was the collection of so called 'fixed' stars that were visible, these being scattered over t...
The December 1639 transit of Venus was only seen and recorded in Much Hoole and Salford, Lancashire, England. It was visible, however, from all over Italy, France, Spain and Portugal. But no one was looking. This paper suggests reasons why.
The D-CIXS Compact X-ray Spectrometer on ESA SMART-1 successfully launched in Sept 2003 can derive 45 km resolution images of the Moon with a spectral resolution of 185 eV, providing the first high-resolution global map of rock forming element abundances.
Out of over 200 known short-period comets, we analyse a self-consistent list of 105 comets which have accurately estimated nuclei radii. It is found that both the median size and the size distribution index of these comets vary as a function of the perihelion distance, q, of the cometary orbit. A value of q≈ 2.7 au divides the comets into an outer...
It is shown that the known trans-Neptunian objects (TNOs) have an absolute magnitude distribution index that increases as
a function of orbital perihelion distance. In no perihelion range is the TNO index the same as that found for known short-period
comets. However, the fact that the median diameters of the known members of these two populations (...
Our knowledge of planetary spin periods is reviewed as are some of the attempts that have been made to explain why planets are spinning as fast as they are.
The smaller members of the solar system hold vital clues as to the composition, history and evolution of the whole. I review the history of discovery of the Edgeworth-Kuiper belt and outer solar-system bodies, and suggest that Pluto, Charon and the newly discovered Quaoar are just the largest members of this belt. Their size distribution indicates...
The D-CIXS X-ray spectrometer on ESA's SMART-1 mission will provide the first global coverage of the lunar surface in X-rays, providing absolute measurements of elemental abundances. The instrument will be able to detect elemental Fe, Mg, Al and Si under normal solar conditions and several other elements during solar flare events. These data will a...
The D-CIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. D-CIXS consists of a high throughput spectrometer, which will perform spatially localised X-ray fluorescence spectroscopy. It will also carry a solar monitor, to provide the direct calibration nee...
Cosmogony, unlike its bigger brother Cosmology, concerns the origin of planets, and not the Universe as a whole. As such, it is a much more relevant subject to the student of physics and astronomy. Living as we do on a fairly typical terrestrial planet, we, as inquiring scientists, must often wonder where our home came from. It is a short step from...
By analysing recent comet catalogues, it is found that the flux of long-period comets to the inner solar system has been reasonably constant throughout the last two millennia. There is no evidence of periods of enhanced activity, or comet showers. The acuity of northern hemisphere naked-eye observers throughout the era of pre-telescopic astronomy w...
When a large asteroid of diameter d hits the surface of the Earth, it produces a crater of diameter D. This paper uses the near-Earth asteroid (NEA) size and miss-distance statistics to calculate the rate at which asteroids hit the Earth. Comparison of this with the known rate at which craters have been produced on the Earth's surface indicates tha...
Focus: comet interceptors: Space research seems the only way to find out more about the small, icy nuclei of comets.
Halley's comet returns to the vicinity of the sun about every 76 years. Between August 1985 and the end of 1986 it is confidently expected that the comet will be brighter than 14th magnitude and thus, under ideal observing conditions, detectable with a telescope smaller than 15 cm objective diameter. The author reviews how one should go about obser...
The magnitude distribution, perihelion distribution, nucleus size variation and evolution of the short-period comet population
are re-assessed. Short-period comets with perihelion distances greater than 2 au have a magnitude distribution index of about
2.3, similar to that of the long-period comets. This index progressively increases for smaller pe...
The purpose of the D-CIXS (Demonstration of a Compact Imaging X-ray Spectrometer) instrument on the ESA SMART-1 mission is to provide high quality spectroscopic mapping of the Moon by imaging fluorescence X-rays emitted from the lunar surface. In order to obtain adequate statistics for what can be very weak sources, it is essential to have a large...
A comparison between the terrestrial, Cytherean and lunar cratering records indicates that the large craters (diameters D>D0) on these surfaces all have cumulative numbers that are proportional to D-2.59±0.05. Atmospheres have a negligible effect on the formation of D>D0 craters. It is shown that this limiting diameter is 45±3 km in the case of Ven...
The macro-features of the surface layer of a ‘fresh’ cometary nucleus are modelled by assuming that the dust and the snow
particles of which it consists both have a mass distribution index of 1.65, and that the dust/gas mass ratio is 0.45. Conclusions
are drawn as to how this model helps us to understand the cometary sublimation process and the com...
The mass distribution and perihelion distribution of long-period comets are re-assessed. The mass distribution index is found to be 1.598±0.016, indicating that the distribution is somewhat steeper than was obtained by previous analyses of an amalgam of all the available historical data. The number of long-period comets that have orbital perihelion...
Galileo tried to measure the diameter of the star Vega (Alpha Lyrae)
using a piece of rope, and realising that he needed to take into account
the finite size of the pupil of the eye, he measured that too. Not only
is it fun to try to repeat these experiments for yourself, they also act
as a great introduction to practical historical astronomy.
Giovanni Antonio Rocca wrote "The problem of solar distance and parallax
was one of the most important in astronomy, well worth a lifetimes work
by any astronomer." (see Ricciolo, 1651:732). This paper briefly reviews
the values obtained for the Earth-Sun distance throughout the history of
astronomy, and divides the investigation of the astronomica...
It is beyond debate that life exists on Earth. It is also quite clear
that comets not only contain large amounts of water, and considerable
amounts of organic material, but also have orbits that enable them to
scatter this material throughout the solar system. But are comets and
life inexorably linked? Would life have broken out on Earth without
co...
The comet should be observable with small telescopes or binoculars for about a year from the late summer of 1985, and with the naked eye for a substantial part of that period. The author describes in detail where to look, and makes suggestions about what to look for. Observers in the Southern Hemisphere will be favoured on this occasion.
The recent cratering record of the surface of the Earth is re-examined using a new technique that concentrates on estimating the mean areas occupied by individual craters, together with the gradients of linear plots of crater numbers versus crater ages. This analysis indicates that the lower limit of the rate at which craters have been produced ove...
The D-CIXS (Demonstration of a Compact Imaging X-ray Spectrometer) instrument will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. At the same time it will demonstrate a radically novel approach to building a type of instrument essential for the Mercury cornerstone mission. It consists...
The velocity distribution of the known periodic comets with perihelion distances less than 1 au is compared with the velocity distribution of the stream meteoroids observed from Earth. The distributions are reasonably similar. The fact that meteor magnitude and electron line density are dependent on impact velocity seems to be more than counterbala...
Over the time span of a decade beginning circa 1940, numerous observers
reported the apparent detection of luminous meteors in a supposed lunar
atmosphere. These observations run counter to our present-day knowledge
and it is now understood that the Moon has no gaseous envelope in which
meteoroid ablation can occur. Before circa 1950, however, the...
The DCIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the lunar surface. In so doing it will also flight test and demonstrate a major technological innovation in the design and construction of X-ray spectrometer instrumentation. Such instruments are essential for surface science studies of Mercury and other atmosph...
The Whipple formula for the emission velocity of meteoroid dust from the surface of a cometary nucleus is reviewed and it is concluded that, in normal circumstances, the dust velocity is ‘low’, typically being less than 20% the radial gas velocity. If, however, the dust particle contains some embedded snows when it leaves the cometary nucleus, its...
Oral mnemonic systems for transmitting or representing melodies are examined in several diverse music cultures, to demonstrate that certain acoustic—phonetic features of vowels and consonants lead to similar systems of mnemonics existing independently in widely separated cultures. The primary relevant features are Intrinsic Pitch, Intrinsic Intensi...
Caroline Herschel (1750-1848) was an active astronomer at a time when
discovering comets, and calculating their orbits, was one of the main
astronomical activities. She discovered eight comets and held the
ladies' world record in this field until April 1987 when she was toppled
from the podium by Carolyn S. Shoemaker. This paper places the Herschel...
We interpret the historical activity of comet 55P/Tempel–Tuttle in terms of the observed characteristics of present-day short
period comets. In this respect, it is now realized that such comets are liable to undergo significant outburst and mantle
loss events at intervals separated by of order a few hundred years. On this basis one might well expec...
The D-CIXS Compact X-ray Spectrometer will provide high quality
spectroscopic mapping of the Moon, the primary science target of the
SMART-1 mission. At the same time it will demonstrate a radically novel
approach to building a type of instrument essential for the Mercury
cornerstone mission. It will achieve ground breaking science within a
resourc...
The rate at which the surface of Earth is being cratered can be measured
by analysing the sizes and ages of the craters that are found on certain
stable areas of the Earth's land-mass. The effects of erosion can be
easily accounted for. On the stable areas it is found that, for example,
craters larger than 2.5 km in diameter take longer then 125 My...
The interpretation of the way in which the brightness of a comet varied as a function of both its heliocentric and geocentric distance was essentially started by Isaac Newton in his book Philosophiae Naturalis Principia Mathematica, published in 1687. Astronomers have argued about the form of this variability ever since, and for many years it was r...
Both Asteroid 951 Gaspra and 243 Ida look like smooth, rounded pebbles and neither have the expected angular, jagged-faceted appearance of a rock fragment produced by a hypervelocity impact. We suggest that they were both rough and sharp-edged at birth and that the rounding off that we now see is the result of a multitude of low-velocity collisions...
This paper is part of the special publication Meteorites: flux with time and impact effects (eds M.M. Grady, R. Hutchinson, G.J.H. McCall and D.A. Rothery). The physical phenomena governing planetary cratering can be represented by three equations. The first, the cratering rate equation, originates from the observation of areas of the Earth's land-...
We present the description of a design for a proposed Dust Flux Analyser for the Rosetta cometary mission. A concept first developed for the NASA/ESA Tempel II Rendezvous and Halley Intercept Mission /1/, the instrument is able to measure dust particle parameters and fluxes over a velocity range typical of emission from cometary surfaces. It would...
The interior of a cometary nucleus is probably full of holes, these having a size distribution that echoes that of the major snowball cometesimal components. Considering the compositional similarities between comets and the satellites of the outer planets, coupled with the “fractal” nature of cometary structure it is concluded that comets probably...
H.M. Harrison, Voyager in Time and Space: The life of John Couch Adams, Cambridge Astronomer . The Book Guild Ltd, Sussex, 1994. Pp. 282, £15.00 (Hardbound ISBN 0-86332-918-7). John Couch Adams (1819-1892), Lowndean Professor of Astronomy and Geometry at Cambridge (1858-1892) and Director of the Cambridge Observatory (1861-1892), is unfortunately r...
A sensitive radar in New Zealand has for the first time detected the faint meteors produced by interstellar dust grains hitting the Earth. It even points to nearby, young stars as being among the sources.
This paper reviews the way in which the dust cloud in the inner solar
system is fed by the decay of comets and by interasteroidal collisions.
Both these mechanisms lead to the formation of streams of meteoroid
particles that can be observed on Earth as meteor showers. The orbital
characteristics of these stream particles provide vital clues as to t...
Some theories flourish and some die quickly. In 1864 Sir John Herschel tried to link two fashionable astronomical topics, these being the meteor showers, seen periodically in the Earth's atmosphere, and solar spot activity. Lurking in the wings at that time was the impression that the solar luminosity was obtained from the kinetic energy of impacti...
A diameter of 290+/-15 km separates large spherical asteroids from
smaller non-spherical ones. Theoretical considerations, based on the
assessment of the mean energy associated with the interparticle forces
between each asteroidal atom and its relationship to the gravitational
force present, also indicate that somewhere between diameters of 140 and...
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
The observed semimajor axis distribution of the Perseid stream requires meteoroids to be ejected from the nucleus of P/Swift-Tuttle with velocities that have a Maxwellian distribution, the most probable velocity being about 0.6 km s⁻¹. The mass loss is reasonably symmetrical with respect to the time of perihelion passage. The cometary nucleus spins...
By the analysis of photographic Perseid meteor orbital data the
semimajor axis of the causative meteoroids is found not to vary
systematically as a function of meteoroid mass over the mass range
0.001<m<30 g. The only way that this finding is compatible with
the Whipple formula for the meteoroid ejection velocity from a cometary
nucleus is if the m...
The Perseids usually appear, with no remarkable variation in numbers, every August, maximising about the 12th. They have a parent, Comet Swift-Tuttle (1862 III), and, with the exception of planet Earth, the causative meteoroids keep away from perturbing planets. Of all the known streams the origin and evolution of the Perseids should be the easiest...
The world's most famous meteor shower picture (Fig. 1) is of the storm that took place in the early morning of Wednesday, 13 November 1833. The picture was, however, produce 54 years after the event, being first published in April 1888. It had a biblical origin and was only taken over by the astronomers in the mid 1920s. The artist was the Swiss pa...
The mean collision velocity between an asteroid and the Earth is found to be 20.8 km s−1. The standard deviation of the velocity data about this mean is 6.2 km s−1. The analysis of recently discovered Earth-crossing asteroids shows that the mean Earth-impact velocity decreases as the mean asteroid diameter decreases.
Eleven years ago, Hughes (Mon. Not. R. astr. Soc.199, 1149, 1982) gave the size distribution of 740 asteroids. This has now been updated using 1778 known asteroidal diameters. The mass distribution index of the large main-belt asteroids is now found to be 2.09 ± 0.10. A power law relationship has been obtained between the perihelion distance and th...
In Solar System astrophysics, isolationism is unfashionable and comparative planetology is all the rage. Astronomers compare Venus with Earth, Mars with Moon and Jupiter with Saturn; so why not compare comets with asteroids? This is the task that I set out to fulfil, but it must be stressed at the outset that, just like the previous examples, comet...
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
Popular schematic representations of meteoroid streams are often
incorrect, first with respect to the positioning of the meteoroids
around the "mean" orbit, and second with respect to the cross-sectional
area around the orbit.
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
This paper investigates the Delta Effect, a term that is taken to cover
the quantitative variation of observed cometary brightness as a function
of comet-Earth distance, Delta (as opposed to the more restricted
definition, where it specifically applies to deviations of this
variation from the inverse-square law). We investigate the Delta Effect
in...
Think about an asteroid smashing into the surface of the Moon and excavating a crater; or hitting Earth and scattering meteorite fragments over a strewn field. Imagine a fragment of cometary dust burning out in the Earth's atmosphere and producing a meteor. These bodies have paths that are inclined at some angle to the vertical. But what is the pre...
IN the European Space Agency's 1992 Giotto Extended Mission, the Dust Impact Detection System operated successfully during a fly-by that took the spacecraft within about 200 km of the nucleus of comet Grigg–Skjellerup. During the encounter, three meteoroid impacts were detected on Giotto's front shield. The particle masses were found to be lOO+105...
The beautiful comet that hovers above the Bethlehem stable in Giotto's
`Adoration of the Magi' (the fresco in the Scrovegni Chapel in Padua) is
most probably the bright naked-eye comet of 1304 and not, as is commonly
supposed, the first recorded image of Comet Halley, at its 1301
apparition.
A Tapestry of Orbits. By Desmond King-Hele. Cambridge University Press: 1992. Pp. 244. á£35, $54.95.