P7: Observing the Universe

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Presentation transcript:

P7: Observing the Universe

Convex / Converging Lenses bring light to a Focus

Power (dioptre) = 1 / Focal Length More powerful lenses have more curved surfaces

Simple telescopes have 2 converging lenses Simple telescopes have 2 converging lenses. The most powerful one being the eyepiece lens

Magnification = focal length of objective lens / focal length of eyepiece lens

Astronomical objects are so distant that light from them is effectively parallel Light on the outside of this picture is close to parallel, whereas in the centre it is more at an angle

Concave Mirror Telescopes Concave mirrors bring light to a focus In this telescope, you can think of the concave mirror as being the “objective lens” Most astronomical telescopes are this type

Ray Diagrams Extended off principal axis Label: Source Focal Points Real Image Principal Axis Extended off principal axis

Ray Diagrams Extended Source Label: Source Focal Points Real Image Principal Axis Extended Source

The larger the lens, the sharper the image Telescope must have a larger aperture than the wavelength of radiation detected to produce a sharp image. Larger aperture = less diffraction

Telescopes on Earth Major optical and infrared astronomical observatories on Earth are mostly in Chile, Hawaii, Australia and the Canary Islands

Astronomical Factors for Telescopes High altitudes – Less atmosphere above to absorb light Away from cities – Less light pollution Good number of clear nights

Non-Astronomical Factors Cost of building observatory Environmental impact Social Impact Working conditions for employees

Telescopes in Space Outside Earth’s atmosphere Avoids absorption (Gamma Rays, X-Rays don’t reach Earth’s surface) Avoids refraction of light Very expensive to setup, maintain and repair Uncertainties of Government funding for space programs (EG: Barack Obama has recently cut funding in this area to concentrate on the economy).

International Collaboration Example: Gemini Observatory in Chile Opened 2002 Collaboration between Australia and 6 other countries

Advantages to International Collaboration Cost of manufacturing can be shared Astronomers from around the world can book time on telescopes in different countries. This allows them to see stars on other sides of the Earth Pooling of expertise and equipment

Direct or Remote Access Telescopes Astronomers don’t need to travel to each telescope to be able to use it Can use telescope at convenient times EG: Schools in the UK can access the Royal Observatory over the internet

Computers and Telescopes Can locate a star and track it across the sky Image recorded digitally Computer can enhance image (eg: reduce noise) Can share images with other scientists quickly Computers allow hundreds of people from all over the world to access the same telescope

Parallax Close stars seem to move relative to others over the course of the year.

Parallax Angle Half the angle moved against a background of distant stars in 6 months.

Parallax Angle Size A smaller parallax angle means the star is further away.

Parsecs A star whose parallax angle is 1 arcsecond is at a distance of 1 parsec Calculate distances in parsecs for simple parallax angles expressed as fractions of a second of arc

Light Year / Parsec A parsec is similar in magnitude to a light year 1 Parsec = 3.26163626 Light Years Interstellar distances (distance between stars) are a few parsecs (pc) Intergalactic distances (distance between galaxies) are measured in megaparsecs (Mpc)

Intrinsic Brightness (Luminosity) Total Amount of Radiation the Star Gives Out Per Second Depends on its Temperature and its Size

Observed Brightness Looking at the night sky, 2 stars may seem to be the same brightness. However the intrinsically brighter star may be further away. If you brought the two stars together so that they were the same distance from you, one would stand out as being brighter

Cepheid Variables Cepheid variable pulse in brightness. Their Period relates to their Brightness.

Working Out Distances Using Cepheid Variables Measure the Period Use the Period to work out Intrinsic Brightness Measure the Observed Brightness Compare the Observed Brightness with the Intrinsic Brightness to get the Distance

Discovery of Other Stars and Galaxies Telescopes: Revealed that the Milky Way consists of many stars and led to the realisation that the Sun was a star in the Milky Way galaxy. Also revealed the existance of “fuzzy” objects which originally were named nebulae. Curtis v Shapely Debate: Were Nebulae objects within the Milky Way galaxy or separate galaxies outside it? Hubble: Observed Cepheid Variables in one nebula which indicated that it was much further away than any star in the Milky Way, and hence, this nebula was a completely separate galaxy.

Solar v Sidereal Day Sidereal Day 23hrs56mins Solar Day 24 hours

Different stars are seen at different times of the year

Planets move in complicated patterns relative to the “fixed” stars

Describing the Position of a Star 2 angles form Earth are needed: Angle from North to the Star. Angle from the Horizon to the Star.

Solar Eclipse: Sun blocked out Solar Eclipse: Sun blocked out. Rare because the Moon’s orbit is tilted 5 degrees. Lunar Eclipse: Moon blocked out. More common because the Earth’s shadow is so big.

Sun, Stars and Moon Sun, Stars, Moon (and Planets mostly) move across the sky from East to West. IE: everything sets in the West, not just the Sun. This is explained by the Earth’s rotation. Sun: 24 hours Stars: 23 hours 56 minutes Moon: 25 hours The Moon takes 28 days to orbit the Earth completely. It also orbits the Earth from West.

Hot Objects All hot objects emit a continuous range of electromagnetic radiation The greater the Peak Frequency (measured in Hz) the higher the temperature and intrinsic brightness. Which is why hot blue objects (high frequency) are hotter than a hot red objects (low frequency)

Ionisation Ionisation is the removal of an electron from an atom.

Electrons move within Atoms Electrons can also move between electron shells within an atom This produces line spectra Each element has a unique line spectra

Star Spectrum Star spectra contain specific spectral lines. These provide evidence of the elements in the star

Rutherford-Geiger-Marsden Experiment

Describing the Experiment Expected Results: alpha particles passing through the plum pudding model of the atom undisturbed. Observed Results: a small portion of the particles were deflected, indicating a small, concentrated positive charge (the nucleus).

The Model of the Atom Past → Present

Structure of the Atom Saturday, April 22, 2017 Page 34 - 35

The Source of the Sun’s Energy Up until the mid 19th Century (1850) it was commonly believed that the Sun was composed of some special material that had the ability to shine eternally. Advancements in the true structure of the atom led to the source of the Sun’s energy. If you could somehow force the protons present in the nuclei of hydrogen together to form helium nuclei, this would release energy as light and heat.

Nebula Nebula are clouds of dust, hydrogen and helium. These materials "clump" together to form larger clumps. More mass = more gravity = more mass attracted

Protostar Proto = Prefix meaning “first”

Compressed Gases Increased pressure Particles closer together More collisions with other particles Friction and collisions between particles increases the temperature

Decreased Volume Increased Pressure Increased Temperature

Absolute Zero The lowest possible temperature All particles/atoms stop moving completely Gas would exert no pressure

Two Competing Forces in the Formation of Protostars Pressure of Compressed Gases Gravity between the particles of gas

Two Competing Forces Something is holding these smurfs together even though they are trying to pull away from each other

Strong Nuclear Force Something is holding this Nucleus together even though the protons want to pull away from each other.

Nuclear Fusion Hydrogen fusing together to make Helium atoms. This releases lots of energy.

Structure of the Sun Core – Fusion takes place Radiative Zone – Energy transported towards the surface by photons Convective Zone – Energy transported to surface by convection Photosphere – Energy is radiated into space

When Hydrogen runs out Stars start to change.

Average size stars (like out Sun) turn into Red Giants Massive stars turn into Red Supergiants.

Red Giants and Red Super Giants Higher elements are made by just fusing more Helium nuclei together: Carbon Oxygen Nitrogen This Fusion process also releases energy What elements are living organisms made from? What element has been made in this diagram?

Red Giants Red giants lack the mass to compress the core further at the end of helium fusion. They then shrink into hot white dwarfs, which gradually cool.

Red Super Giants Fusion Continues in Red Supergiants Due to the high pressure in their core larger elements are formed

Red Super Giants Fusion stops in Red Super Giants when the core is mostly Iron (Fe)

Supernova Exlosion After the core is mostly iron, and fusions stops, a Supernova explosion occurs which ejects much of the star’s materials

Neutron Stars and Black Holes After a Supernova Explosion, the remaining material turns into a Black Hole or Neutron Star Both of these are extremely dense objects