4
1 Introduction
Astronomy is arguably the oldest of the sciences—the positions of the stars, the
Moon, and planets have been used for thousands of years to determine times for the
sowing and harvesting of crops and for navigating the seas. The temporal power of
the Mayan priesthood rested partly on their ability to reliably predict eclipses, and
many ancient monuments across the world feature astronomical alignments as part
of their design. Astronomy’s prehistory segues into what we would now consider
astrology, just as chemistry has its origins in alchemy. Astronomy was clearly established as an actual, recognisable science only as recently as the seventeenth century.
Sir Isaac Newton’s formulation of the theory of gravity was an essential achievement,
as it provided a systematic theoretical foundation to what had previously been something of a disorganised grab-bag of facts, half-truths, and conjecture. Because of this
extensive pre-history, modern astronomy contains many odd and quirky traditions
(as an example, the sexagesimal coordinate system originated with the Babylonians).
You may well find some of these oddities rather disorienting at first. However, you
will get used to such quirks in time.
Throughout this book, we have preferentially used the SI unit system. There are
some deviations from this rule, as astronomy has plenty of non-SI measures, such
as, for instance, the parsec, the jansky, and the astronomical unit. Where there is a
suitable SI unit, though, we will be sticking to that, so you won’t be bedevilled by
angstroms or ergs. You will find Joules and nanometres, though. If you need to use
a non-SI unit, please remember to make the appropriate conversion.
Before we move on, let’s briefly define a couple of these unavoidable non-SI units.
The astronomical unit (AU) is the median separation between the Earth and the Sun.
It’s equal to 149,597,870,700 m. The AU is most often used in dealing with distances
inside the solar system. The Parsec (pc) is the distance at which an object would show
a parallax displacement of one second of arc. It equates to 3.08567758 × 10
16 m.
Kiloparsecs (Kpc; 1 Kpc = 1,000 pc) and megaparsecs (Mpc; 1 Mpc = 1,000,000 pc)
are also often used in astronomy. For the most distant observable objects, the distance
is expressed in terms of the degree of observable cosmological redshift (z). Higher-z
objects are further away, but the scale isn’t linear, and moreover, the actual distance
will depend on the cosmological model being used. As a point of reference, objects
at z = 1 are roughly halfway to the edge of the observable universe, whereas the
cosmic microwave background is at z = 2,000. (The CMB effectively constitutes
the “edge” of the observable universe for all practical purposes.)
1.4 Introduction: Best Practice
The observatory that you will be using is a laboratory, just like any other that you
may have worked in. As such, you should treat it as a lab—read and understand the
safety guidelines and the operating instructions before you begin observing. It is very
likely that there will be specific documentation relating to the use of the observatory.
You need to make yourself aware of what is in those documents, and if you have any
questions, it’s a good idea to ask a member of the observatory staff.
1 Introduction
Astronomy is arguably the oldest of the sciences—the positions of the stars, the
Moon, and planets have been used for thousands of years to determine times for the
sowing and harvesting of crops and for navigating the seas. The temporal power of
the Mayan priesthood rested partly on their ability to reliably predict eclipses, and
many ancient monuments across the world feature astronomical alignments as part
of their design. Astronomy’s prehistory segues into what we would now consider
astrology, just as chemistry has its origins in alchemy. Astronomy was clearly established as an actual, recognisable science only as recently as the seventeenth century.
Sir Isaac Newton’s formulation of the theory of gravity was an essential achievement,
as it provided a systematic theoretical foundation to what had previously been something of a disorganised grab-bag of facts, half-truths, and conjecture. Because of this
extensive pre-history, modern astronomy contains many odd and quirky traditions
(as an example, the sexagesimal coordinate system originated with the Babylonians).
You may well find some of these oddities rather disorienting at first. However, you
will get used to such quirks in time.
Throughout this book, we have preferentially used the SI unit system. There are
some deviations from this rule, as astronomy has plenty of non-SI measures, such
as, for instance, the parsec, the jansky, and the astronomical unit. Where there is a
suitable SI unit, though, we will be sticking to that, so you won’t be bedevilled by
angstroms or ergs. You will find Joules and nanometres, though. If you need to use
a non-SI unit, please remember to make the appropriate conversion.
Before we move on, let’s briefly define a couple of these unavoidable non-SI units.
The astronomical unit (AU) is the median separation between the Earth and the Sun.
It’s equal to 149,597,870,700 m. The AU is most often used in dealing with distances
inside the solar system. The Parsec (pc) is the distance at which an object would show
a parallax displacement of one second of arc. It equates to 3.08567758 × 10
16 m.
Kiloparsecs (Kpc; 1 Kpc = 1,000 pc) and megaparsecs (Mpc; 1 Mpc = 1,000,000 pc)
are also often used in astronomy. For the most distant observable objects, the distance
is expressed in terms of the degree of observable cosmological redshift (z). Higher-z
objects are further away, but the scale isn’t linear, and moreover, the actual distance
will depend on the cosmological model being used. As a point of reference, objects
at z = 1 are roughly halfway to the edge of the observable universe, whereas the
cosmic microwave background is at z = 2,000. (The CMB effectively constitutes
the “edge” of the observable universe for all practical purposes.)
1.4 Introduction: Best Practice
The observatory that you will be using is a laboratory, just like any other that you
may have worked in. As such, you should treat it as a lab—read and understand the
safety guidelines and the operating instructions before you begin observing. It is very
likely that there will be specific documentation relating to the use of the observatory.
You need to make yourself aware of what is in those documents, and if you have any
questions, it’s a good idea to ask a member of the observatory staff.