Distance determination is an essential technique in astronomy, and is briefly covered in most textbooks on astrophysics and cosmology. It is rarely covered as a coherent topic in its own right. When it is discussed the approach is frequently very dry, splitting the teaching into, for example, stars, galaxies and cosmologies, and as a consequence, books lack depth and are rarely comprehensive.
Adopting a unique and engaging approach to the subject An Introduction to distance Measurement in Astronomy will take the reader on a journey from the solar neighbourhood to the edge of the Universe, discussing the range of distance measurements methods on the way. The book will focus on the physical processes discussing properties that underlie each method, rather than just presenting a collection of techniques.
As well as providing the most compressive account of distance measurements to date, the book will use the common theme of distance measurement to impart basic concepts relevant to a wide variety of areas in astronomy/astrophysics.
The book will provide an updated account of the progress made in a large number of subfields in astrophysics, leading to improved distance estimates particularly focusing on the underlying physics. Additionally it will illustrate the pitfalls in these areas and discuss the impact of the remaining uncertainties in the complete understanding of the Universes at large. As a result the book will not only provide a comprehensive study of distance measurement, but also include many recent advances in astrophysics.
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Yes, you can access An Introduction to Distance Measurement in Astronomy by Richard de Grijs in PDF and/or ePUB format, as well as other popular books in Physical Sciences & Astronomy & Astrophysics. We have over one million books available in our catalogue for you to explore.
The Importance of Astrophysical Distance Measurements
When we try to pick out anything by itself, we find it hitched to everything else in the Universe.
– John Muir (1838–1914), American naturalist and explorer
Each problem that I solved became a rule, which served afterwards to solve other problems.
– René Descartes (1596–1650), French philosopher
Accurate distance measurements are of prime importance for our understanding of the fundamental properties of both the Universe as a whole and the large variety of astrophysical objects contained within it. But astronomical distance measurement is a challenging task: the first distance to another star was measured as recently as 1838, and accurate distances to other galaxies – even the nearest – date only to the 1950s, despite evidence of the existence of ‘spiral nebulae’ as early as Lord Rosse's observations in the mid-nineteenth century. This is not surprising, since the only information we have about any object beyond our solar system includes its position (perhaps as a function of time), its brightness (as a function of wavelength and time) and possibly its radial velocity and chemical composition.
While we can determine highly accurate distances to objects in our solar system using active radar measurements, once we leave the Sun's immediate environment, most distance measurements depend on inferred physical properties and are, therefore, fundamentally uncertain. Yet at the same time, accurate distance measurements on scales of galaxies and beyond are crucial to get a handle on even the most basic questions related to the age and size of the Universe as a whole as well as its future evolution. The primary approach to obtaining distance measurements at increasingly greater distances is by means of the so-called distance ladder, where – in its most simplistic form – each rung is calibrated using the rung immediately below it. It is, therefore, of paramount importance to reduce the statistical uncertainties inherent to measuring distances to even the nearest star clusters in our Milky Way, because these objects are the key benchmarks for calibrating the cosmic distance scale locally. In this book, we take the reader on a journey from the solar neighbourhood to the edge of the Universe, en passant discussing the range of applicable distance measurement methods at each stage. Modern astronomers have developed methods of measuring distances which vary from the mundane (the astronomical equivalent of the surveyor's theodolite) to the exotic, such as the bending of light in general relativity1 or using wiggles in the spectrum of the cosmic microwave background (CMB).
Not only do we provide an up-to-date account of the progress made in a large number of subfields in astrophysics, in turn leading to improved distance estimates, but we also focus in particular on the physics underlying the sometimes surprising notion that all of these methods work remarkably well and give reasonably consistent results. In addition, we point out the pitfalls one encounters in all of these areas, and particularly emphasize the state of the art in each field: we discuss the impact of the remaining uncertainties on a complete understanding of the properties of the Universe at large.
Before embarking on providing detailed accounts of the variety of distance measurement methods in use, here we will first provide overviews of some of the wide-ranging issues that require accurate determinations of distances, with appropriate forward referencing to the relevant chapters in this book. We start by discussing the distance to the Galactic Centre (Section 1.1). We then proceed to discuss the long-standing, although largely historical controversy surrounding the distance to the Large Magellanic Cloud (LMC) (Section 1.2). Finally, in Section 1.3 we go beyond the nearest extragalactic yardsticks and offer our views on the state of the art in determining the 3D structure of large galaxy clusters and large-scale structure, at increasing redshifts.
1.1 The Distance to the Galactic Centre
The Galactic Centre hosts a dense, luminous star cluster with the compact, nonthermal radio source Sagittarius (Sgr) A
at its core. The position of the latter object coincides with the Galaxy's kinematic centre. It is most likely a massive black hole with a mass of
M
(see the review of Genzel et al. 2010), which is – within the uncertainties – at rest with respect to the stellar motions in this region. The exact distance from the Sun to the Galactic Centre, R
, serves as a benchmark for a variety of methods used for distance determination, both inside and beyond the Milky Way. Many parameters of Galactic objects, such as their distances, masses and luminosities, and even the Milky Way's mass and luminosity as a whole, are directly related to R
. Most luminosity and many mass estimates scale as the square of the distance to a given object, while masses based on total densities or orbit modelling scale as distance cubed. This dependence sometimes involves adoption of a rotation model of the Milky Way, for which we also need to know the Sun's circular velocity with high accuracy. As the best estimate of R
is refined, so are the estimated distances, masses and luminosities of numerous Galactic and extragalactic objects, as well as our best estimates of the rate of Galactic rotation and size of the Milky Way. Conversely, if we could achieve a highly accurate direct distance determination to the Galactic Centre, this would allow reliable recalibration of the zero points of a range of secondary distance calibrators, including Cepheid, RR Lyrae and Mira variable stars (Sections 3.5.2, 3.5.5 and 3.5.3, respectively), thus reinforcing the validity of the extragalactic distance scale (cf. Olling 2007). In turn, this would enable better estimates of globular cluster (GC) ages, the Hubble constant – which relates a galaxy's recessional velocity to its distance, in the absence of ‘peculiar motions’ (see Section 5.1) – and the age of the Universe, and place tighter constraints on a range of cosmological scenarios (cf. Reid et al. 2009b).
1.1.1 Early Determinations of R
The American astronomer, Harlow Shapley (1918a,b), armed with observations of GCs taken with the Mount Wilson 60-inch telescope (California, USA) since 1914, used the light curves of Cepheid variables and, hence, the...
Table of contents
Cover
Title Page
Copyright
Dedication
Preface
Chapter 1: The Importance of Astrophysical Distance Measurements
Chapter 2: The Solar Neighbourhood
Chapter 3: From the MilkyWay to the Local Group
Chapter 4: Reaching Virgo Cluster Distances and Beyond
Chapter 5: From Nearby Galaxy Clusters to Cosmological Distances
Chapter 6: Systematic Uncertainties and Common Pitfalls
