Astonomy 10

Telescopes

“A bucket for light!”

• Refracting telescope: 

  • focuses light lenses

    • Need to be very long, with large, heavy lenses

• Reflecting telescope: 

  • focuses light with mirrors

    • Can have much greater diameters

    • Most modern telescopes

Radio Telescope

• A radio telescope is like a giant mirror that reflects radio waves to a focus

Atmosphere is trouble for all telescopes except for radio waves

IR & UV telescopes

• Infrared and ultraviolet light telescopes operate like visible light telescopes but need to be above the atmosphere to see all IR and UV wavelengths

Calm, High, Fark, Dry

• The best observing sites are atop remote mountains 

• Rapidly changing the shape of a telescope's mirror compensates from some of the effect of turbulence 

Resolution

• How much detail does the picture contain 

  • High definition = better 

• Pixel size = Wavelength/Diameter of telescope 

  • Small wavelength is better, big telescope is better 

Interferometry 

• Using an array of telescopes to act like a single large telescope 

  • A bunch of telescopes that act like a big telescope

• Involves breaking up the telescope into pieces

• Can only do it with radio waves because it does not care about the atmosphere

  • Could do in space but too expensive

• But if you were to do it in space it would work with anything

• Picture of a black hole 

  • Using radio wave

  • Black holes are not big

Adaptive optics 

• Change the shape of the telescope to compensate for the distortion of the atmosphere

James Webb Telescope

• Latest telescope 

• Planetary/galaxy birth 

• Best Infrared b/c in space = very cold

The Sun 

Nuclear Energy 

• E=MC2

• Einstein, 1905

• All mass has a lot of energy stored in it 

• Nuclear Potential Energy (core) . Luminosity ~ 10 billion years 

Chemical energy 

• Hydrogen + oxygen = H2O

• Surface of the sun is called the Photosphere

  • Relatively cold (4,000K)

  • Core is hot (10^7K)

Two types of nuclear energy: Fusion & Fission, e.g., both changing atoms so nuclear energy

Fusion 

• Putting together atoms

• What the sun and stars do

• 4H-> He+ gamma rays & neutrinos

  • Fusing Hydrogen together to make helium and it comes in gamma rays(light)

  • Nothing nuclear

• The fuel has to be very hot

• Small nuclei stick together to make a bigger one 

Fission 

• Breaking up atoms 

• Big nucleus splits into smaller pisces 

• What we do in power plants

• Atoms with a lot of protons

  • Uranium, plutonium 

  • Radioactive

Gravitational contraction 

• Provided energy that heated core as Sun was forming 

• Contraction stopped when fusion began

Chromosphere

• Not visible to the naked eye (except during solar eclipses)

• 20,000 K (hotter than the photosphere)

• Very Dynamic and active

Corona

• Outermost layer of the solar atmosphere

  • 1 million K

• Photosphere 

  • Outerlayer of the sun 

  • Visible surface of the Sun 

  • 6,000 K

  • Coldest place in the sun 

• Convection Zone

  • Boiling gas

    • “Lava lamp” “cooking Spaghetti”

  • Energy transported upward by rising hot gas

• Radiation Zone

  • Energy transported by protons 

• Core

  • Center of the sun

  • Only place hot enough to generate nuclear fusion 

  • Energy generated by nuclear fusion 

Fusion of Hydrogen - P-P reaction 

• Proton-proton reaction 

Overall reaction 

• The sun fuses hydrogen 

  • fuel

• Puts them together and makes helium 

• Then becomes a gamma ray and then a neutrino 

• Neutrinos created during fusion fly directly through the sun 

• Observations of these solar neutrinos can tell what what's in the core

  • 4H -> He + gamma rays + neutrinos

Gamma rays

• The energy comes from fusion 

• Inside the sun light is slow

  • Drunk light zone

  • Bouncing around to the surface of the sun

• By the time it reaches the surface it is no longer gamma rays 

  • Visible light 

Density 

• Density = mass/volume 

Solar Neutrino problem 

• Early searches for solar neutrinos failed to find the predicted number

• More recent observations find the right number of neutrinos, but hace changes form

  • In the sun neutrinos are faster than light 

  • Produced at the center 

  • Are not faster than light just phase through everything

Earth

• Has iron at the center

• Is mainly constructed of rock

• Has small percent of water 

Stars

• THe brightness of a star depends on both distance and luminosity

• Luminosity

  • How bright i the stat

  • Actuall brightness og intuitive brightness

    • “Absolute magnitude”

  • L=4pi R2T4

  • Brightness = (Size of star squared)(temperature of star)

• Apparent brightnes

  • How bright it seems to us

    • apparent brightness + distance = luminosity

• Two reasons why a star is so bright

  • Closest to you

  • It is actually really bright far away

One star equals the bright of 1million og the sun

Properties of Thermal Radiation

• Hotter objects emit more light per unit area at all frwuencies

• Hotter objects emit photons with a higher reqhencie

  • Red star is cold

    • O stars means hot

  • A blue star is hot

    • M stars red cold

How do we measure stellar masses 

• Eclipes 

• A orbit of a binary star system depends on strength of gravity 

Two types of star clusters 

• Open cluster 

  • Stars are everywhere 

    • O & M

    • All colors 

• Globolar clustar 

  • Stars everwhere

    • No O stars

    • O stars blew up 

    • Red an yellow

Interseller Reddening

• Stars viewed through the edges of the cloud look redder because dust blocks (shorter - wavelength) blue light more effectively than (longer-wavelength) red light 

• The longer the wavelength the easier it is to get throught the pollution 

• Infrared light reveal stars on the other side of the cloud

Planet Detection Methods

• Eclipse method 

  • Transit

  • Looking for shadows

    • Nest method

    • Bill barookie

• Doppler Method “Wobble method

  • Is the star wobobling

    • If yes, than a planet makes it wobble 

    • Found Hot jupiters

• Gravitational lensing

  • Planets can make the start background glitch

    • Microlensing

  • Gravity bends light (blackholes)

• FLoating planets