Abstract
In this chapter we will discuss what kind of observations informed our picture of the universe. To this end we will discuss briefly electromagnetic radiation, the various forms of “light”, and also briefly touch on “non-standard messengers” such as neutrinos and gravitational waves. We can then ask, how are these observations actually made? This will allow us to highlight some recent telescopes and experiments.
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Notes
- 1.
The term “Big Bang” is not very well defined. Here we mean very early on in the history of the universe. Throughout the book we use the phrase “the beginning” to denote the beginning of the universe.
- 2.
Electromagnetic waves or photons can also be affected by other photons, but this effect is very small. Overall the universe is “charge-neutral” and there are therefore no electric forces on large scales, and the magnetic fields on large scales are extremely tiny and have a very small effect on the photons.
- 3.
Photons are also produced in these processes, but they interact, get scattered, many times before they reach the surface of the star. We can therefore only “see” the outer layers of the Sun, for example.
- 4.
Claudius Ptolemaeus (about 100–170), Roman Astronomer and Mathematician, influential works on geometry and astronomy.
- 5.
In this model, the motion of the planets is explained by the planet moving on a small circle, the centre of which moves on a larger circle. The “epicycle” is this movement of a circle on a circle.
- 6.
Galileo Galilei (1564–1642), Italian astronomer, physicist and engineer, groundbreaking works in physics and astronomy.
- 7.
Friedrich Wilhelm Herschel (1738–1822), German astronomer working in London, made early maps of the universe.
- 8.
Caroline Lucretia Herschel (1750–1848), German astronomer working in London, made early maps of the universe.
- 9.
Some theoreticians—not us—joke that the mirrors are reshaped to produce the images observers want.
- 10.
“Near infrared” refers to radiation with wavelengths near to the optical range.
- 11.
Karl Guthe Jansky (1905–1950), American physicist and engineer, pioneering work in the area of radio astronomy.
- 12.
Grote Reber (1911–2002), American engineer, pioneering work in the area of radio astronomy.
- 13.
Arno Allan Penzias, (1936–), and Robert Woodrow Wilson (1936–), both American physicists and astronomers, discovered the Cosmic Microwave Background.
- 14.
NASA launched during “Project Echo” in 1960 balloons with metallised surfaces and roughly 30 m diameter into a low Earth orbit, and reflected microwaves off the balloon back to a receiver on Earth.
- 15.
George Gamow (1904–1968), American physicist, influential works in cosmology.
- 16.
Also roughly 1% of the static on old TV sets (with aerials) is due to the Cosmic Microwave Background radiation.
- 17.
Cherenkov radiation comes about when a charged particle travels through a medium with a speed higher than the speed of light of the medium (the speed of light in matter is smaller than the speed of light in vacuum).
- 18.
We would like to apologise to our colleagues for the many omissions!
- 19.
Euclid of Alexandria (around 300 bc), Greek mathematician, major works attributed in geometry.
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Malik, K.A., Matravers, D.R. (2019). What Observations Do We Use?. In: How Cosmologists Explain the Universe to Friends and Family. Astronomers' Universe. Springer, Cham. https://doi.org/10.1007/978-3-030-32734-7_3
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DOI: https://doi.org/10.1007/978-3-030-32734-7_3
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