Unit 2 Flashcards
Instruments, solar system, atmosphere, etc.
What forms the image in a telescope?
The objective (lens or mirror)
What magnifies the image in a telescope?
The eyepiece
What are the two main types of telescopes?
Refractor (the objective is a lens)
Reflector (the objective is a mirror)
What kind of telescope is the Newtonian telescope?
Reflector
What type of telescope did Galileo use?
Refractor
What are the three “powers” of a telescope?
Light-gathering power
Resolving power
Magnifying power
What does better light-gathering power mean?
You can see dimmer objects
What is the aperture of a telescope?
The diameter of the objective
What is light-gathering power measured by?
The area of the objective
What does better resolving power mean?
You can better see details
What is resolving power measured by?
The resolution of the instrument as an angle (theta R)
On Earth, what is our resolution limited by?
The turbulence of the atmosphere (~0.5”)
What are some solutions to the limitations of our resolving power on Earth?
1) Go to space
2) Correct the image with adaptive optics (Lazer beams)
What does better magnifying power mean?
Objects look bigger
What is magnifying power measured by?
Angular magnification (the ratio of focal lengths of he objective and eyepiece respectively)
What is the rule of thumb for magnification of telescopes?
The maximum magnification is twice the diameter of the objective in milimeters.
What are the different types of electromagnetic radiation from high wavelength to low wavelength?
Radio waves Microwaves Infrared Visible Ultraviolet X-rays Gamma rays
What types of objects emit electromagnetic radiation?
All objects
What are the two rules that govern the spectra of various objects?
1) if an object is hot, the peak of it’s spectrum will occur at a small wavelength (bluer)
2) hotter objects emit more (per unit surface) (Stephane’s Law)
What instrument do astrophysicists use to measure the spectra of an object?
Spectrometer
Which electronic transition series constitutes the visible spectrum?
Balmer Series
Which part of the electromagnetic spectrum constitutes the Lyman series?
Ultraviolet
Which part of the electromagnetic spectrum constitutes the Paschen series?
Infrared
What are the terrestrial planets?
Mercury, Venus, Earth, Mars
Why have terrestrial planets lost most of their atmosphere?
They are hotter (closer to the sun)
They have a smaller gravity (less mass)
What are the Jovian planets?
Jupiter, Saturn, Uranus, Neptune
What are some properties of the Jovian planets?
Gaseous Giants Made mostly of H and He Cold Many satellites Rotate around themselves fast
Which is denser: Terrestrial planets or Jovian planets?
Terrestrial (has much less H and He)
What is another name for asteroids?
Minor planets
What EM waves does our atmosphere block?
Most except visible light and radio waves
What is another name for spectral power?
Radiance (or Intensity)
What can the spectrum of light tell us about objects?
Temperature, chemical composition, velocity, etc.
What is a blackbody?
A body that does not reflect light but emits some based on it’s temperature of equilibrium
When an object is moving towards Earth is the resulting redshift positive or negative?
Negative (it will be a blue shift)
Why is Pluto an exception to the the planets (and was this called a kuipler object)?
It looks like a terrestrial planet but very cold, very elliptical orbit that is inclined, and a member of the kuipler belt.
Where are asteroids located?
Between Mars and Jupiter
What sis the largest asteroid?
Ceres
What are asteroids made of?
Rock and ice (some organic compounds)
Where are comets located (generally)?
Oort’s cloud
What are the two tails of a comet?
Gas tail and dust tail
What is special about our moon?
It is quite large compared to it’s planet
Does the moon have a magnetic field?
No
Is the moon denser or less dense than Earth?
Les dense
Is the moon denser or less dense than Earth?
Les dense
What planet does the satellite Io belong to?
Jupiter
What is special about Europa?
- Covered by fractured ice
- Probably has an ocean of liquid water underneath.
What is Ganymede?
The largest of the Galilean moons
What is the name of the largest moon on Saturn?
Titan
How does Titan look?
Rocky surface with a thick atmosphere (made mostly of nitogen).
What is special about Triton (a moon of Neptune)?
It has retrograde motion (rotation is opposite to the rotation of it’s parent planet)
Has gesyers of boiling liquid nitrogen
A kuipler belt object captured by Neptune?
What determines the temperature of a planet?
The distance from the star that warms it,
But also the planet’s albedo and green house effect
What is the albedo of a planet?
The percentage of light that is reflected back into space
What is the green house effect of a planet?
The percentage of light that is trapped by the planet’s atmosphere
What does the Boltzmann distribution consist of?
A graph of # of molecules (on the y-axis) and velocity representing the statistical distribution particles at various velocities.
What is the v rms ?
The root mean square of the velocities of the particles that is related to the temperature.
What is brightness and what does it depend on?
Rate at which we receive energy
Depends on the luminosity and the distance
What is luminosity what is it a physical property of?
Rate at which a star emits energy
A physical property of a star
How much does luminosity range in stars?
About 10 billion times (10^-4 to 10^6)
How does the spectrum of a star tell us it’s surface temperature?
The position of the peak wavelength tells us the temperature
What does Wien’s law tell us?
That hotter stars have a peak at lower wavelengths
What is the full sequence of spectral types from hot to cold?
OBAFGKM (oh, be a fine girl, kiss me)
What do stronger absorption lines tell us?
It is either a really hot or cold star
What is the most direct way of determining the distance from stars?
Trigonometric parallax (change in angular position caused by displacement of the observer)
What is a parsec measured by?
The distance at which a star would have a parallax of 1 arcsecond
How do we calculate the size of a star?
With luminosity and temperature
What is the flux of a star?
The energy emited per second and per square meter (Stefan’s law)
How do we measure the chemical composition of stars?
Absorption lines
What determines the chemical composition of stars?
Their “stellar populations” (generation)
Describe population I stars.
Most common stars
Found in the disks of galaxies
Contain some elements heavier than He
Describe population II stars.
Found in galactic halos
Very poor in elements heavier than He
Describe population III stars.
Not found yet
Should only contain H and He
How do we determine the motion of a star relative to us?
The position change of the absorption lines over time (Doppler effect)
In a binary system, how do we determine the mass?
By measure the velocities from Doppler shifts and finding the mass using Kepler’s third law
If a star has a mass lower than 0.08 times time mass of the Sun, what do we call it?
A brown dwarf (failed star)
What does the HR diagram plot?
Various stars based on their luminosity and surface temperature
When a star stars running out of fuel, it leaves the main sequence to become a ___ or a ___.
Giant or supergiant
How can we determine the main sequence lifetime (Tms)?
It is the energy available over the rate at which energy is consumed (luminosity)
The luminosity is proportional to the fourth of the mass.
The amount of energy available is proportional to the mass.
Thus the Tms is inversely proportional to the third of the mass.
What is the Corona of a star?
The outer layer of the sun composed of gas
What are the two fundamental balances stars need to not ex/implode?
Hydrostatic equilibrium (outward pressure = inward pressure) Rate of energy emitted (L) = rate of energy produced
What is hydrogen burning?
The FUSION of hydrogen ions into helium
Happens to all main sequence stars
What is the rate of nuclear reactions of a star effected by?
The mass of the star
Why is iron not be fused into something else (generally) in stars?
Most stars are not massive enough to reach Fe fusion
But most importantly, iron has the largest absolute binding energy (meaning can reaction that separates the nucleus will use more energy than outputted when rejoined)
Where does the energy come from when H is fused into He?
The mass of the resultant He is less than the original H ions. (The mass deficit)
Write the nuclear equation of the first step of the pp chain
1H^+ + 1H^+ –> 2H^+ + e^+ + v + energy
What category of particle do the proton and the neutron fall under?
Nucleons
What does the start of pp chain require?
Two Hydrogen nuclei hitting together (one turning into a proton) and creating a deuterium nucleus, a positron (to be soon annulated with an electron), a neutrino and energy released
What is the reaction in the pp chain that fuses He?
1H^+ + 2H^+ + 3He^++ + released energy
What is another method of fusing He for energy in a star (other than the pp chain)?
The CNO cycle (uses carbon as a catalyst for H burning)
Describe the CNO cycle.
A carbon 6+ ion hits a H+ ion releasing gamma radiation and nitrogen 7+, this can either decay back to carbon or fuse with a H+ into oxygen 8+ which decays into N^7+ which splits into a carbon 6+ and He^2+
Why is the CNO cycle only used in stars of higher temperature?
The carbon 6+ and hydrogen + repel each other and thus need higher temperatures to collide. At this point the CNO cycle is much more efficient than the pp chain.
When the hydrogen of a star is used, what does it try to fuse at first but decays back into helium and what does I succeed in fusing after?
It tries to fuse two 4He^++ into 8Be^4+ but it is unstable so it fuses instead three 4He^++ into 12C^6++
What ia special about Io?
Smallest Galilean moon
Covered by lava
Heated up by the tidal force exerted by Jupiter
