Transcript: The Doppler Effect is the shift of wavelength or frequency of a source of waves due to the motion of that source of waves. Doppler Effect is most familiar in terms of sound waves. As a source of sound, such as a siren, approaches you, the pitch or frequency increases. As it moves away from you, the pitch or frequency decreases. You can see that if a source of waves is moving towards you, the waves will be bunched up in the direction of motion, and so the wavelength will be...

Transcript: German physicist Gustav Kirchhoff experimented with hot gases in the laboratory in the mid-nineteenth century and deduced three laws of radiation that apply to all astronomical objects in space. The first is that a hot gas or sufficiently hot solid will emit with a continuous spectrum of radiation or a continuum. The second is that a hot gas will emit only certain bright wavelengths of radiation called emission lines. Each element emits its distinct and unique set of emission...

Transcript: When a hot object like a star is surrounded by a cooler layer of gas or has an intervening cool material we see an absorption spectrum. Always they’re at the smooth thermal radiation reflecting the temperature of the object itself, but in the case of an outer or intervening cool layer of gas the radiation is absorbed by the cooler gas exciting those atoms that then reradiate in all directions causing notches in the spectrum or lowering of the intensity at the exact position...

Transcript: When a hot object like a star is observed directly, two types of radiation are seen at the same time. One is the smooth continuous spectrum or thermal spectrum whose peak wavelength reflects the temperature of the object being observed. For a star like the Sun emitting yellow light, this peak wavelength is in the visible spectrum, and the surface temperature of the sun is at about 5,700 Kelvin. In addition to the smooth radiation of the thermal spectrum the hot or ionized gas...

Transcript: Advances in technology have caused a surge in our ability to understand the universe. After 30 or more years where the Palomar 5-meter Telescope was the largest useful telescope on the ground, we now have a dozen or more 8 to 10-meter class telescopes with which to study the distant universe. Large optical telescopes of apertures 30 to 50 meters are planned. In space NASA has completed the launch of its Great Observatories spanning the electromagnetic spectrum from x-rays and...

Transcript: For all regions of the electromagnetic spectrum where radiation does not penetrate the Earth‘s atmosphere, astronomy must be done from space. This includes gamma rays, x-rays, ultraviolet radiation, far infrared, and some kinds of millimeter waves. Space astronomy is expensive compared to ground-based astronomy. Typical launch costs are ten thousand dollars per kilogram, and so space telescopes are intrinsically more expensive then ground-based telescopes. A small ground-based...

Transcript: The biggest optical telescope can see about 10 billion times fainter then the human eye. This is the enormous advance of astronomy in the last 400 years since the invention of the telescope. Where does this huge factor come from? It comes from three different pieces. First the aperture of a 10-meter telescope compared to the roughly 1-centimeter aperture of the eye is a factor of a thousand. Second, the efficiency of optical detectors, CCDs, compared to the chemical detection...

Transcript: Interferometry is a technique that astronomers have developed to improve the performance of a telescope. A single telescope has its resolution limited by the diameter of the primary mirror. However, in principle it is possible to use two or more telescopes separated by a distance, point them at the same object, and combine their signals. If the signals are combined coherently, that is timing measurements are used to combine the peaks and troughs of the light exactly, then you...

Transcript: Image processing is essential to modern astronomy. Astronomical data is obtained in the form of digital information captured using a charged coupled device or CCD detector. Astronomers use image processing for various purposes. They use it to dig out faint signals in CCD images because objects as stars and galaxies are detected in the presence of a background from the night sky. Even when the night sky looks totally dark with no moonlight there is residual brightness due to...

Transcript: The most basic information about an astronomical object is the amount of light that it emits; this is photometry. We learn more, however, when we can disperse the light from an astronomical object into a spectrum; this is called spectroscopy. Spectroscopy gives us the opportunity to see the spectral transitions of the atoms contained within the object whether it’s a planet, or a star, or a galaxy, and this in turn gives us information on the chemical composition, information...

Transcript: Astronomers measure the radiation from distant astronomical objects in several ways. The most basic information is called photometry. This is just a calibrated measure of the amount of light coming from an astronomical object. The light is gathered by the telescope and is collected, and the number of photons is counted or inferred from the brightness on a CCD image. Photometry is a measure of the light from an object defined over a specific range of wavelengths. Astronomers...

Transcript: If you work out the angular resolution of a four meter telescope in optical waves of light it should be about two hundredths of an arcsecond. The images obtained by a single four meter mirror are never this good because of the blurring effect of the Earth’s atmosphere. Essentially turbulence in the upper levels of the atmosphere jumbles the light rays as they go through the atmosphere and blurs the image by a significant degree. Most ground-based observatories have intrinsic...

Transcript: Essentially all modern telescopes used by research astronomers are reflecting telescopes. They use mirrors to bend, deflect, and focus light to form an image. The first reflecting telescope was perfected by Isaac Newton, and reflecting telescopes of larger and larger aperture have been produced ever since. Edwin Hubble discovered the distant nature of galaxies and the expansion of the universe using the largest reflecting telescope at the time just outside Los Angeles. For...

Transcript: The fundamental purpose of a telescope is to gather light. There are two important ways of characterizing a telescope. One is in terms of the light gathering power or how much radiation is gathered and then focused into an image. The light gathering power depends on the area of a telescope and so goes up as the diameter or radius of a mirror squared. Thus a telescope of twice the diameter has four times the light gathering power. A telescope of three times the diameter, nine...

Transcript: The two processes by which light is gathered in a telescope are refraction and reflection. In refraction, light, when it travels from a less dense to a more dense medium, is slowed down, and when the light ray arrives at an angle of incidence the wave is refracted or bent. The amount by which the light bends depends on color or wavelength. Blue light travels slower in a physical medium light glass then red light, and so the blue light is bent more. Thus, when white light...

Transcript: Astronomy is unusual among the sciences because there is almost no direct experimentation, unlike the situation for physics, and biology, and chemistry. In astronomy we have almost never traveled to the places that we study with the exception of the Moon and robotically to some of the planets and moons in the solar system. Almost everything we learn about the universe is a matter of remote sensing that is radiation that we receive from space. This radiation allows us to...

Transcript: The early twentieth century was a time of innovation and revolution in both science and the arts. Scientists used the quantum theory to delve deep into the structure of nature and produce new representations of matter. Artists were doing the same thing, exploring new representations of the natural world in painting and in sculpture. They were also taking different forms of representation beyond the traditional view; relativity was a part of this revolution in science. These...

Transcript: The quantum theory of matter imbeds the idea of probability in a fundamental way. There is no certainty when it comes to talking about atoms and fundamental particles. This is embodied most clearly in Heisenberg’s Uncertainty Principle where, when we know the position of a particle or atom, its momentum is not perfectly well determined; if we know its momentum, its position is not well determined. And so in the quantum theory the wave-particle duality of matter and radiation...

Transcript: In the quantum theory there is a profound connection between the observer and the thing being observed, and this leads to some interesting philosophical consequences. Einstein was uncomfortable with the quantum theory, and he created some examples to illustrate its strangeness. One of these is the idea of Schrodinger’s cat. Schrodinger was a German physicist who worked on the theory in the 1920s and 30s. In Schrodinger’s cat the idea is of a cat trapped in a box where you...

Transcript: The quantum theory imbeds in a fundamental way idea indeterminacy and imprecision. Heisenberg’s Uncertainty Principle sets a fundamental limit on our knowledge of the physical world independent of the degree of observations or the quality of the measuring apparatus. Einstein in particular was very uncomfortable with this aspect of the quantum theory which is called the Copenhagen Interpretation. Einstein believed that there was a deeper and more fundamental theory that would...

Transcript: Each element in the periodic table has a unique number of protons and electrons. Each element also therefore has a unique set of energy levels for the atom. That unique set of energy levels maps into a unique set of spectral features of either emission or absorption. Thus the spectral lines from an element are a fingerprint unique to that element. In astronomy spectral features can be used to detect tiny concentrations of different elements. When the elements are mixed in a...

Transcript: Atoms produce sharp spectral features of emission or absorption corresponding to the specific energy states of the atom. Each element has its own set of energy states. Atoms that are grouped into molecules have a much larger set of possible energy states, in part because they share electrons and in part because they can vibrate and oscillate many different ways. This large set of possible energy states produces a large set of corresponding spectral transitions. Often, these...

Transcript: Atoms gain energy by collisions or by absorbing photons of radiation. However atoms cannot absorb photons with any energy or wavelength. The energy states of an atom are quantized so atoms can only gain energy according to wavelengths that correspond to the energy difference between electron energy levels. This removal of waves of a certain value leaves dark features in the spectrum or absorption lines. Since atoms that are raised in energy eventually reemit photons, why do...

Transcript: When a hot object like a star is observed directly, two types of radiation are seen at the same time. One is the smooth continuous spectrum or thermal spectrum whose peak wavelength reflects the temperature of the object being observed. For a star like the Sun emitting yellow light, this peak wavelength is in the visible spectrum, and the surface temperature of the sun is at about 5,700 Kelvin. In addition to the smooth radiation of the thermal spectrum the hot or ionized gas...

Transcript: Neils Bohr was a Danish physicist who won the Nobel Prize early in the last century. One of the towering figures of modern physics, he established an institute in Copenhagen that was a Mecca for physicists from all around Europe. Bohr was an architect of the modern view of the atom within the quantum theory of a nucleus surrounded by electrons that could only take fixed energy levels. Bohr believed deeply in the quantum theory and had violent arguments with Einstein who...