Revision Notes Astronomy - Concepts Of The Universe (PHYS295): courses, PDF

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Lecture 7 – Exp-Solar Planets Three Key Properties of Solar System:   

Size and composition of terrestrial versus Jovian planets Geometry of the planets orbits Size of the terrestrial versus Jovian planet orbits

Nebula Hypothesis: A diffuse, roughly spherical, slowly rotating nebula begins to contract and as a result, a flat, rapidly rotating disk forms. (Called the Kelvin-Helmholtz contraction) Terresital Planets – accretion of dust into planetesmials and then larger protoplanets Jovan Planets – Core accretion of gases onto rocky-ice core. Planets around other stars only assumed until 1995. Now detected by astrometric method (look for the motion of the star (wobbles) about the center of mass), the radial velocity method (Look for the periodic Doppler shifts in the star's spectral lines as it moves about the center of mass), the transit method (look for the drop in the star's brightness as an exoplanet cuts across its disk along our line of sight). Kepler Mission – determine abundance of terrestrial and larger planets in habitable zone, there shapes, sizes, densities and properties. Kepler – 185 (first earth size planet in habitable zone) Gravitational Microlensing- because light rays are bent when they pass close to a massive object, light from a distant source may be focussed by a closer object to producing a sudden brightening. When a small nearby star passes directly between the Earth and a more distant star, the smaller object's gravitational field acts as a lens to bend and focus the light. Miller/Urey Experiment – put molecules which were believed to represent the major components of the early earth’s atmosphere and put them into a closed system. Ran continuous electric current through it as to represent early earth conditions. Organic carbon compounds produced that are essential to cellular life. Lecture 9 – Impact Threat Torino Scale expresses the hazard and probability of collision with earth in diagrammatic form. Large asteroids are rarely a threat. However objects the size of a small car hit a few times a year. Most asteroids are found in circular orbits between mars and Jupitaer however recently discovered the Amors, the Atens and the Apollos all Near Earth Objects. Comets are small icey bodies which orbit the sun in highly elliptical paths Tunguska – 1908, seismic tremors circled the globe, blast inject millions of tons of dust intothe atmosphere resulting in cooler temperatures across the globe. 80 m diameter meteorite.

Water on Mars Has there been water? Riverbeds and gullies indicate that water ran, at least briefly, across the surface of Mars. A hundred times more water may have flowed annually through a large channel system known as Marte Vallis than passes through the Mississippi River each year, according to estimates. If you have veins, then you have had water that has some sort of rock-forming mineral solution that has dissolved in the water, transported somewhere else and then deposited again.       

Tharisis Glaciers(high plains) potentially past glaciers as shown by location and shape of simulated glaciers with the actual deposits of Tharirsis The Valleys (mariner valley) Mesas Dendritic Valleys Seepage (undermining material causing erosion above site of seepage) Ice impacts (central holes not peaks, bed ejects, impact into fluid material) Normally 1m deep and lower

How long did it exist for and when? Where did it go? Vast deposits of water appear to be trapped within the ice caps at the north and south poles of the planet. Each summer, as temperatures increase, the caps shrink slightly as their contents skip straight from solid to gas form, but in the winter, cooler temperatures cause them to grow to latitudes as low as 45 degrees, or halfway to the equator. Lecture 10 - Stars Gamma, X-ray, UV, Visible, Infrared, Micowave, Radio X-rays and gamma rays are produced by matter which is heated to millions of degrees (cosmic explosions, collisions). Ultraviolet – to study these wavelengths, high altitude balloons, rockets and orbits are used. Only young massive stars and very old stars, bright nebulae, white dwarfs, active galaxies and quasars shine brightly in UV. Infrared –primarily heat radiation ( can penetrate thick regions of dust in apce and is therefore used to peer into star forming regions into the central areas of our galaxy) Radio Waves (during day and night can be detected, used to study first detection of left over radiation from big bang) Distance:  

Direct method (stellar parallax) Standard candles (objects of known luminosity)

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Standard rulers (objects of known size)

Parallax is the apparent displacement of an object because of a change in the observers point of view. Distance (pc)=1/parallax angle (arcseconds) Luminosity – Energy emitted by a star per second (measured in Watts) Apparent brightness – amount of energy that passes each second through a square meter Inverse square law (W/m2) 𝑏=

𝐿 4𝜋𝑑 2

We can determine the luminosity of a star from its distance and apparent brightness. For a given distance, the brighter the star the more luminous the star must be. For a given apparent brightness, the more distant the star, the more luminous it must be to be seen at that distance. Magnitude scale, used to denote the brightness of stars. Hipparchus divided the stars into classes dependant on their brightness. 6 so called magnitudes, 1st order brightness, 6th just visible, each magnitude twice the brightness of the following. (ALL APPARENT) Apparent magnitude is measure of a stars appartent brightness as seen from Earth Absolute magnitude is the apparent magnitude a star would have it were located 10parsec from earth. (measure of a stars luminosity). Stars colour is directly related to its surface temperature Weins Law: peak wavelength(microns)=2900/T(k) Astronomers can accurately determine the surface temperature of a star by carefully measuring its colour. OBAFGKM – Oh be a fine girl, kiss me 0-9 attatched O is the hottest Note: now LT have been added for even lower surface temperatures of brown dwarfs Star composition – mostly ¾ Hydrogren, ¼ Helium and...