The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

The introductory lecture delivered at the Symposium has covered the subjects itemized above with the exclusion of Sections 10, 11, 14, 18, and 19.

For the last two decades, significant and dramatic progress has been made in understanding astrophysical jet sources, particularly in the X-ray and gamma-ray energy bands. For example, the Chandra X-ray observatory reveals a number of AGN jets extending from kpc to Mpc scales. More recently, the Fermi Gamma-ray Space Telescopes launched in 2008 started monitoring the gamma-ray sky with excellent sensitivity of about ten times greater than that of EGRET onboard CGRO, and has detected more than 2,000 sources (mostly AGNs) as of 2014. Moreover, Fermi-LAT has discovered gamma-ray emissions not only from blazars but from a dozen radio galaxies not previously known to emit gamma-rays. Closer to home, the Fermi-bubbles were discovered to extend 50 degrees above and below the Galactic center. These large scale diffuse gamma-ray structures are similar in structure to AGN lobes such as those seen in Cen A and provide evidence for past activity in our Galactic center. In this review, I will first summarize recent highlights of large scale jets in radio galaxies, specifically resolved by the Chandra X-ray observatory. Next I will move on to the gamma-ray sky to present some highlights from Fermi-LAT observations of “misaligned” blazars, namely radio galaxies. I will discuss a unification scheme connecting blazars and misaligned radio galaxies. In the last part, I will also briefly comment on recent multiband observations of the Fermi-bubble and possible impacts on the AGN jet physics in the near future.

Although the radio emission from most quasars appears to be associated with star forming activity in the host galaxy, about ten percent of optically selected quasars have very luminous relativistic jets apparently powered by a SMBH which is located at the base of the jet. When these jets are pointed close to the line of sight their apparent luminosity is enhanced by Doppler boosting and appears highly variable. High resolution radio interferometry shows directly the outflow of relativistic plasma jets from the SMBH. Apparent transverse velocities in these so-called “blazars” are typically about 7c but reach as much as 50c indicating true velocities within one percent of the speed of light. The jets appear to be collimated and accelerated in regions as much as a hundred parsecs downstream from the SMBH. Measurements made with Earth to space interferometers indicate apparent brightness temperatures of ~ 1014 K or more. This is well in excess of the limits imposed by inverse Compton cooling. The modest Doppler factors deduced from the observed ejection speeds appear to be inadequate to explain the high observed brightness temperatures in terms of relativistic boosting.

Welcome to Beijing and IAU XXVIII General Assembly. Although the world economic situation continues to show stress, the science of astronomy is flourishing on many fronts. True, we are not immune to the negative effects of sharply reduced funding for projects and positions, yet our do-main sees increased international collaboration, pioneering facilities and techniques in development, and significant discoveries that are changing the way humanity thinks about the universe and our place in it. Programs that the IAU has undertaken such as the United Nations International Year of Astronomy 2009 and the creation of the Office of Astronomy for Development in Cape Town have been hugely successful.

The asteroids (more precisely: objects of the main asteroid belt) and Kuiper Belt objects (more precisely: objects of the cold classical Kuiper Belt) are leftovers of the building material for our earth and all other planets in our solar system from more than 4.5 billion years ago. At the time of their formation those were typically 100 km large objects. They were called planetesimals, built up from icy and dusty grains. In our current paradigm of planet formation it was turbulent flows and metastable flow patterns, like zonal flows and vortices, that concentrated mm to cm sized icy dust grains in sufficient numbers that a streaming instability followed by a gravitational collapse of these particle clump was triggered. The entire picture is sometimes referred to as gravoturbulent formation of planetesimals. What was missing until recently, was a physically motivated prediction on the typical sizes at which planetesimals should form via this process. Our numerical simulations in the past had only shown a correlation between numerical resolution and planetesimal size and thus no answer was possible (Johansen et al.2011). But with the lastest series of simulations on JUQUEEN (Stephan & Doctor 2015), covering all the length scales down to the physical size of actual planetesimals, we were able to obtain values for the turbulent particle diffusion as a function of the particle load in the gas. Thus, we have all necessary data at hand to feed a 'back of the envelope' calculation that predicts the size of planetesimals as result of a competition between gravitational concentration and turbulent diffusion. Using the diffusion values obtained in the numerical simulations it predicts planetesimal sizes on the order of 100 km, which suprisingly coincides with the measured data from both asteroids (Bottke et al.2005) as well from Kuiper Belt objects (Nesvorny et al.2011).

Radio astronomy began with one array (Jansky's) and one paraboloid of revolution (Reber's) as collecting areas and has now reached the point where a large number of facilities are arrays of paraboloids, each of which would have looked enormous to Reber in 1932. In the process, interferometry has contributed to the counting of radio sources, establishing superluminal velocities in AGN jets, mapping of sources from the bipolar cow shape on up to full grey-scale and colored images, determining spectral energy distributions requiring non-thermal emission processes, and much else. The process has not been free of competition and controversy, at least partly because it is just a little difficult to understand how earth-rotation, aperture-synthesis interferometry works. Some very important results, for instance the mapping of HI in the Milky Way to reveal spiral arms, warping, and flaring, actually came from single moderate-sized paraboloids. The entry of China into the radio astronomy community has given large (40-110 meter) paraboloids a new lease on life.

Items of scientific knowledge at any moment in time have pre-histories when they were debated, doubted, or absolutely denied. The examples considered here are the admitted facts that star formation is an on-going process in the Milky Way, that there are young moving groups (the products of young star clusters in the process of dissolution and perhaps more complex processes), and that planets orbiting other stars are common. It is hard to imagine any of these ceasing to be part of core astronomical knowledge, but you are advised not to place large bets on this.

Our knowledge of the dynamics and masses of galaxies in the Local Group has long been limited by the fact that only line-of-sight velocities were observationally accessible. This introduces significant degeneracies in dynamical models, which can only be resolved by measuring also the velocity components perpendicular to the line of sight. However, beyond the solar neighborhood, the corresponding proper motions have generally been too small to measure. This has changed dramatically over the past decade, especially due to the angular resolution and stability available on the Hubble Space Telescope. Proper motions can now be reliably measured throughout the Local Group, as illustrated by, e.g., the work of the HSTPROMO collaboration. In this review, I summarize the importance of proper motions for Local Group science, and I describe the current and future observational approaches and facilities available to measure proper motions. I highlight recent results on various Milky Way populations (globular clusters, the bulge, the metal-poor halo, hypervelocity stars, and tidal streams), dwarf satellite galaxies, the Magellanic Clouds and the Andromeda System.

We describe an innovative statistical approach for the ab initio simultaneous analysis of the formation history and morphology of the large-scale structure of the inhomogeneous Universe. Our algorithm explores the joint posterior distribution of the many millions of parameters involved via efficient Hamiltonian Markov Chain Monte Carlo sampling. We describe its application to the Sloan Digital Sky Survey data release 7 and an additional non-linear filtering step. We illustrate the use of our findings for cosmic web analysis: identification of structures via tidal shear analysis and inference of dark matter voids.

We live in a universe filled with galaxies with an amazing variety of sizes and shapes. One of the biggest challenges for astronomers working in this field is to understand how all these types relate to each other in the background of an expanding universe. Modern astronomical surveys (like the Sloan Digital Sky Survey) have revolutionised this field of astronomy, by providing vast numbers of galaxies to study. The sheer size of the these databases made traditional visual classification of the types galaxies impossible and in 2007 inspired the Galaxy Zoo project (www.galaxyzoo.org); starting the largest ever scientific collaboration by asking members of the public to help classify galaxies by type and shape. Galaxy Zoo has since shown itself, in a series of now more than 30 scientific papers, to be a fantastic database for the study of galaxy evolution. In this Invited Discourse I spoke a little about the historical background of our understanding of what galaxies are, of galaxy classification, about our modern view of galaxies in the era of large surveys. I finish with showcasing some of the contributions galaxy classifications from the Galaxy Zoo project are making to our understanding of galaxy evolution.

Arguably two of the most important questions in Astrophysics today are: what is the Universe made of? and, how do galaxies form and evolve? Quite astonishingly we know only the properties of < 5% of the mass in the Universe (the atoms we are made of), while the nature of the dominant mass component (the dark matter) remains elusive. However, because of its abundance, dark matter is a significant driver of both the dynamics of stars and galaxies and of their formation and evolution.

The President of the IAU, Prof. Robert Williams, welcomed the delegates and members to this first business session of the General Assembly. The President invited the General Secretary, Dr. Ian Corbett, to start the business session.

The standard Bayesian model formalism comparison cannot be applied to most cosmological models as they lack well-motivated parameter priors. However, if the data-set being used is separable, then it is possible to use some of the data to obtain the necessary parameter distributions, the rest of the data being retained for model comparison. While such methods are not fully prescriptive, they provide a route to applying Bayesian model comparison in cosmological situations where it could not otherwise be used.

Type Ia supernovae remain one of Astronomy's most precise tools for measuring distances in the Universe. I describe the cosmological application of these stellar explosions, and chronicle how they were used to discover an accelerating Universe in 1998 - an observation which is most simply explained if more than 70% of the Universe is made up of some previously undetected form of ‘Dark Energy’. Over the intervening 13 years, a variety of experiments have been completed, and even more proposed to better constrain the source of the acceleration. I review the range of experiments, describing the current state of our understanding of the observed acceleration, and speculate about future progress in understanding Dark Energy.

Erosive collisions among planetary embryos in the inner solar system can lead to multiple remnant bodies, varied in mass, composition and residual velocity. Some of the smaller, unbound debris may become available to seed the main asteroid belt. The makeup of these collisionally produced bodies is different from the canonical chondritic composition, in terms of rock/iron ratio and may contain further shock-processed material. Having some of the material in the asteroid belt owe its origin from collisions of larger planetary bodies may help in explaining some of the diversity and oddities in composition of different asteroid groups.

The capture and disruption of stars by supermassive black holes (SMBHs), and the formation and coalescence of binaries, are inevitable consequences of the presence of SMBHs at the cores of galaxies. Pairs of active galactic nuclei (AGN) and binary SMBHs are important stages in the evolution of galaxy mergers, and an intense search for these systems is currently ongoing. In the early and advanced stages of galaxy merging, observations of the triggering of accretion onto one or both BHs inform us about feedback processes and BH growth. Identification of the compact binary SMBHs at parsec and sub-parsec scales provides us with important constraints on the interaction processes that govern the shrinkage of the binary beyond the “final parsec”. Coalescing binary SMBHs are among the most powerful sources of gravitational waves (GWs) in the universe. Stellar tidal disruption events (TDEs) appear as luminous, transient, accretion flares when part of the stellar material is accreted by the SMBH. About 30 events have been identified by multi-wavelength observations by now, and they will be detected in the thousands in future ground-based or space-based transient surveys. The study of TDEs provides us with a variety of new astrophysical tools and applications, related to fundamental physics or astrophysics. Here, we provide a review of the current status of observations of SMBH pairs and binaries, and TDEs, and discuss astrophysical implications.

KMOS is a multi-object near-infrared integral field spectrograph built by a consortium of UK and German institutes for the ESO Paranal Observatory. KMOS completed commissioning at the ESO VLT in Spring 2013 and was made available to the user community from Oct 2013. We present the unique capabilities of KMOS for 3D galaxy surveys and report on the on-sky performance verification measured during three commissioning runs on the ESO VLT in 2012/13 and some of the early science results.

The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected with a test statistic (TS) greater than 25 using the first 4 years of data. The 3LAC includes 1591 AGNs located at high Galactic latitudes, |b| > 10 (with 28 duplicate associations, thus corresponding to 1563 gamma-ray sources among 2192 sources in the 3FGL catalog), a 71% increase over the second catalog based on 2 years of data. A very large majority of these AGNs (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. The general properties of the 3LAC sample confirm previous findings from earlier catalogs, but some new subclasses (e.g., intermediate- and high-synchrotron-peaked FSRQs) have now been significantly detected.

In 1811, François Arago observed the disk of the Sun with his “lunette polariscopique”. From the absence of detectable polarization compared with his laboratory observations of glowing solids, liquids, and flames he concluded that the Sun's visible surface is an incandescent gas. From this beginning, thanks to orders of magnitude technology improvements, a remarkable amount of what we know about the physics of the Sun has continued to flow from solar polarimetry. This short review compares some selected polarimetric discoveries with subsequent recent observations to illustrate the tremendous progress of solar polarimetry during the last two centuries.

Studies of molecular clouds and young stars near the sun have provided invaluable insights into the process of star formation. Indeed, much of our physical understanding of this topic has been derived from such studies. Perhaps the two most fundamental problems confronting star formation research today are: 1) determining the origin of stellar mass and 2) deciphering the nature of the physical processes that control the star formation rate in molecular gas. As I will briefly outline here, observations and studies of local star forming regions are making particularly significant contributions toward the solution of both these important problems.