General

• Mass of celestial bodies like star is calulated from a relation between its luminosity and spectral stuff ??

• Distant stars are useful for navigation

  • They are so distant that their change in position is not that visible from earth
  • Nearby stars which are close enough for their position change to be visible are not used to guide navigation

• Degrees of freedom (science): number of parameters that may be changed independently

  • Eg: X and Y coordinates in XY-plane

• 6 degrees of freedom

  • Left-right
  • Up-down
  • Forward-backward
  • Roll: angle change sideways
  • Yaw: angle change in horizontal plane
  • Pitch: angle change in vertical plane
  • https://en.wikipedia.org/wiki/Six_degrees_of_freedom

• From the earth, planets appear to move from east to west

  • Because of earth's rotation
  • All stars rise in the east because it's earth that is rotating, not the stars

• Position of planets like mars change because unlike moon, its rotation is not mainly focused on the earth

• Andromeda galaxy

  • Galaxy closest to Milky way
  • The only galaxy observable with naked eye

• Skymap

• Big stars die out faster

• Low-mass stars live longer

  • Low-mass stars are like 'fossils of universe'
  • There are such stars whose life expectancy from now is more than the current age of universe

• Sagan quote: "we're all stardust"
• Some stars 'eat' other stars
  • https://www.space.com/symbiotic-stars-eat-each-other-beyond-milky-way
• Mass of sun:
  • Observe luminoisty and temperature => mass derivable
  • HR-diagram
  • https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram
• Original elements = just H and He
  • All other elements are result of star explosions??
  • High mass elements are formed in star cores (and shell of stars??)
• Binary stars
  • System of two stars that are gravitationally bound to and in orbit around each other. Usually visible as single star to naked eye.
  • Orbits of the two start are dependent on each other ??
  • Eg: Sirus (A and B)
• First stars in the universe
• Sub-atomic particles:
  • Neutrino: Thought to be mass-less
  • Positron: Particles of anti-matter
    • Electron with positive charge
• Gamma rays
  • Most energetic in the light spectrum
  • Deadly to humans
• Main sequence: a stage in the life of a star

• Categories of stars based on temperature (coolest to hottest): M, K, G, F, A, B, O
  • Spectral class from Morgan-Keenan (MK) system
  • Sub-categories are numbers ∈ [0,9]
  • Corresponds to spectral type ??
• Categories of stars based on luminosity: 0 to VII (Roman numerals)
  • Luminosity class
• Eg: Sun is G2V
  • G2: temperature
  • V: Luminosity class
• Chandrasekhar limit = approx 1.4 solar mass
  • Maximum mass of a stable white dwarf

Solar system:

• Saturn:
  • Has rings
  • Most number of moons: 146 moons
• Jupiter
  • Biggest planet
  • 95 moons: Including Europa, Io, Callisto
• Mercury and Venus have no moons
  • Due to sun being more powerful
  • https://spaceplace.nasa.gov/how-many-moons/en/

Misc:

• Useful apps: SkyMap, stellarium

Constellations

• Constellations are groups of stars

• Orion:

  • 'The hunter'
  • Characteristic 'belt': a line of three stars
  • Red star to the left of the 'belt': Betelgeuse (Thiruvathira)
  • Bright star to the right of the 'belt': Rigel

• Gemini

  • Near Mars
  • Brightest stars: Castor and Pollux (twins)
  • Castor, Pollux and Mars form a triangle with the twins as the base

Telescope

• Usually kept pointing north
  • Allows 5 degrees of freedom this way ??
• Spectroscopy
• Reflective
• Refractive
• Space telescope
  • Stable environment. No abrupt temperature changes or cloudy skies.
  • Eg: Hubble (sent by Discover space shuttle)
  • Eg: Chandra (by NASA, not ISRO. Deployed by Columbia space shuttle)
  • Eg: Spitzer (deactivated in 2020)
  • Eg: Webb

Gravitational force

From Newton's law of universal gravitation:

      m₁m₂
F = G ----
       r²

G is the gravitational constant with an approximate value of 6.67 * 10⁻¹¹ m³.kg⁻¹.s⁻²

+-----+             +-----+
|  m₁ | → F₁   F₂ ← |  m₂ |
+-----+             +-----+

   |         r         |     
   +-------------------+     

Sun

• Sun is a low mass star.
• A yellow dwarf
  • https://spaceplace.nasa.gov/all-about-the-sun/en/
• A day of sun: 25-36 earth days (depending on the location in sun)
• Star that's closest to Earth
• Sun's atmosphere = corona
  • https://spaceplace.nasa.gov/sun-corona/en/
• Solar wind
• Solar cycle
  • Around 11 years
  • Starts and ends at Solar minimum
  • Middle part = Solar maximum, when there are most sun spots
  • A complete solar cycle => sun's poles switch places
  • https://spaceplace.nasa.gov/solar-cycles/en/
• Sun spots
  • Dark spots
  • Dark because they are cooler
  • Caused due to strong magnetic fields
• Solar flares
  • A sudden explosion
  • A big enough solar flar can disrupt radio communication on earth
• Solar mass = mass of sun
  • A standard unit of mass in astronomy

nebula
|
v
|
main sequence
|
v
|
red giant
|
v (explode)
|
supernova ---------------->---------------+
|                                         |
v (remnant ∈ [1.4, 3] solar mass)         v (remnant > 3 solar mass)
|                                         |
neutron star                              black hole
|
v
|
white dwarf
|
v (cools)
|
black dwarf

       +------+ <-     
earth  | moon | <-  sun
       +------+ <-            

+------+ <-     
| moon | <-  sun
+------+ <-            

            earth