Midterm Study 2 Flashcards
Telescopes - Why are they needed?
Telescopes are needed to gather information from space. Most of the knowledge we gain from space is through light, and so a telescope needs a mirror or lens with a high diameter to capture as much light as possible to gain the most information as possible.
Seeing with just our eyes limits the information we can gather, so building larger, more powerful optic devices assist us in learning more about and from space.
Main things telescopes do:
Light gathering, magnification, resolution
Light gathering power is influenced by what?
The size/diameter of the primary mirror
Focal length of a telescope determines what?
The magnification and field of view of a telescope
What are the main types of telescopes?
Refractive and reflective
Characteristics of refractive telescopes:
use lenses where the main lens is called the objective lens;
stable against temperature variations;
cleaning the exterior lens is relatively simple;
materials affected by the refractive index;
are complicated to manufacture and thus they can reasonably only get so big
Characteristics of reflective telescopes:
uses a mirror to reflect light to the eyepiece where the main mirror is called the primary mirror;
two main types of reflectors are Newtonian and Cassegrain
Hubble Space Telescope is a reflector
There is a fundamental limit as to what you can resolve (resolution), called the Rayleigh Limit
θ=1.22λ/D
Where θ is the smallest resolvable angle in radians, λ is the wavelength in meters, and D is the diameter of the telescope’s primary mirror/lens in meters
To observe smaller objects, we need to observe at shorter wavelengths, or with bigger telescopes
To observe smaller objects, we need to observe at shorter wavelengths, or with bigger telescopes
Refractors suffer from…?
Chromatic aberration - the material effect produced by the refraction of different wavelengths of electromagnetic radiation through slightly different angles, resulting in a failure to focus. It causes colored fringes in the images produced by uncorrected lenses.
What can correct refractors’ main issues?
Achromatic and apochromatic lenses
Reflectors/mirrors suffer from…?
Spherical aberration - a loss of definition in the image arising from the surface geometry of a spherical mirror or lens.
What can correct reflectors’/mirrors’ main issues?
Parabolic or hyperbolic mirrors can correct this, but they are extremely expensive and very difficult to manufacture
Why do we put telescopes higher up on Earth?
To avoid atmospheric scintillation- Atmospheric scintillation is the twinkling of stars and other distant objects that occurs when light from those objects passes through Earth’s atmosphere. It’s caused by turbulence in the atmosphere, which bends light through the layers of the atmosphere in a process called refraction.
Low scintillation/atmospheric turbulence = ?
Better seeing
Adaptive Optics - ?
use a laser guide star to measure the deformation of the wavefront, and we deform the mirror in response to cancel out the deformed wavefront
Terrestrial Planets
- Made of rocks or metals
- Surfaces are solid
- No rings
- Very few or no moons
- Relatively small
Mercury, Venus, Earth, Mars
Jovian Planets / Giant Planets
- Gas giants: made of hydrogen and helium
- Ice giants: contain rock and ice
- No solid surface
- Support ring systems
- Multiple moons
- Immense size
Jupiter, Saturn, Uranus, Neptune
Equilibrium Temperature
the temperature at which the energy radiated by a planet exactly balances the energy absorbed by the planet
Equilibrium: Temperature and Planets
- Radiation laws accurately predict the temperature of planets without atmospheres
- Distant planets are cold mainly because of the inverse square law of light
- There is a balance of heating and cooling
Static Equilibrium
the physical state of the system, in which the components of the system are at rest and the net force acting on a system should be zero
Equilibrium
Balance
Earth-Moon System Theories
Capture Theory
moon is a captured asteroid that formed elsewhere in the solar system. Relies on some very “good luck,” and thus is not very favored.
Earth-Moon System Theories
Condensation Theory
Earth and Moon formed from the same nebula material at the same time. Doesn’t explain why they have different compositions (If this was the case, they should have near identical compositions, but they do not).
Earth-Moon System Theories
Impact Theory
Earth collided with a Mars-sized planetesimal very early on. Lots of material ejected from Earth’s crust. This theory can explain why the moon is made mostly of rock and why the Earth has a thin crust.
Solar Nebular Theory
The primary atmosphere is the gas initially captured from the disk (H + He mostly).
- This is primarily hydrogen and helium (low mass gases)
- The process by which it catches these gases is called core accretion gas capture
- Giant planets have primary atmospheres because they have been able to hold onto lighter molecules
Solar Nebular Theory
Secondary atmospheres occur around some low mass planets as they couldn’t hold their primary atmosphere and underwent volcanic outgassing (Mostly CO_2 and N_2)
- The low mass planets do not have enough gravity to keep the initial atmosphere
- Volcanoes emit heavy gases such as CO and methane; these are easier to hold on to
- Comets bring water and other volatiles to planets which evaporate and add to the second atmosphere
Solar Nebular Theory
The tertiary atmosphere of Earth is primarily due to life. It is defined by three things:
One: Minimal Carbon Dioxide
* CO_2 is locked away in carbon sinks
* The oceans
* Organic matter
* Chemical reactions in the sea
Two: Abundant Oxygen
* Oxygen O_2 is super reactive – it likes to bind to everything (most metal ores are some sort of oxide, rust is an oxide, for example)
* However, because of photosynthesis, the oxygenation rate was higher
than the oxidation rate, so the oxygen content of the atmosphere grew
Three: Ozone Layer
* Oxygen is O_3 – the bonds between the molecules are the right size to absorb UV which protects life on Earth
* However, each absorption destroys a molecule (called photodissociation)
* Ozone must be regenerated constantly – UV light breaks up O_2 which leaves a spare molecule to form ozone (because a single O is very reactive)
Problems with the Solar Nebular Theory
Tilt of the Planets
- If the planets formed from the same disk, they should have similar angles of tilts
Problems with the Solar Nebular Theory
Timescales
- At 10 million years, we know from observations that a debris disk was left
- There’s no gas – it’s just dust and planetesimals left
- But planets like Jupiter and Saturn are supposed to need 10 million years of orbiting through gas to form in this core accretion model
Core Accretion Theory of Planet Formation
- Dust and ice coagulate: Small dust grains and ices clump together to form larger particles.
- Planetesimals form: These particles stick together to form planetesimals, which are objects that are 1–100 km in size.
- Planetesimals collide: Gravity causes planetesimals to collide with each other, forming planetary embryos.
- Planetary core forms: The embryos eventually form into a planetary core or protoplanet.
- Gas accretion: If the core reaches a certain mass, it can retain hydrogen and helium gas, which leads to gas accretion.
Occultation
when one celestial object passes in front of another, blocking the view of the object behind it
Transit
celestial objects passing in front of each other, or transiting, as seen from a particular vantage point
Transit Method
A technique used to measure the size of planets by observing how they pass between Earth and their star, blocking some of the star’s light:
Observe the Transit:
- When a planet passes between Earth and its star, it blocks some of the star’s light, causing a dip in the star’s brightness. This dip is called the transit depth.
Measure the Transit Depth:
- The depth of the transit is proportional to the size of the planet. By measuring the transit depth and knowing the star’s radius, you can calculate the planet’s radius.
Measure Other Parameters:
- You can also measure the transit duration, which is how long the planet spends transiting the star. The transit duration depends on how fast the planet is moving in its orbit.
We can measure the mass and find the orbital period of planets using Newton’s version of Kepler’s 3rd Law:
P^2=(4π^2 a^3)/(G(M_Sun+M_planet))
If the mass of the Sun so much larger than the planet then:
P^2≈(4π^2 a^3)/(G(M_Sun))
OR
M=(4π^2 a^3)/(GP^2 )
Where M is mass, a is the semi-major axis of the orbiting object’s orbit, G is Newton’s Gravitational Constant, and P is the orbital period of the orbiting object.
Occultation Timing
〖Diameter〗_planet=V_orbital×t_occultation
Giant Planet Characteristics
- When looking at these planets, we do not see their surfaces, we see their atmospheres
- No abrupt transition from atmosphere to ground
- Atmosphere merges into liquid ocean, then to liquid or solid core
- Atmospheres are thousands of km thick
Other random related shit
* Uranus and Neptune are blue because methane is good at absorbing longer wavelengths of light (red)
* Their color appears blue because that is the wavelength of the light that is reflected
Giant Planets
Days and Seasons
- The giant planets all have very fast rotation rates – a day lasts between 9 and 17 hours
- Rapid rotation causes oblateness – difference between the equatorial and polar radii divided by the equatorial radii
**Obliquity **
Planet tilt (is a major factor in planet seasons)
oblateness=(R_equatorial - R_polar)/R_equatorial
Giant Planets
Clouds
- Jupiter has strong dark bands (belts)
and light bands (zones) - There is a long-lasting giant storm
(Great Red Spot) - Red spot is in southern hemisphere,
rotates anticlockwise - anticyclonic
behavior, high pressure - There also are many smaller storms
- The colors indicate complex chemistry
- Saturn has a similar band structure to Jupiter, but it is less pronounced
- Saturn has violent storms and a feature like Earth’s jet stream
- Infrared observations show details of structure on Uranus
- There is weak bonding on both Uranus and Neptune
- There are small, scattered bright or dark clouds
- These planets have transient large storms (Great Dark Spot on Neptune)
JWST
JWST Primary Mission
Study cosmic history and its phases primarily using its powerful infrared telescope.
Looks at the first galaxies and stars in the universe.
JWST
JWST Secondary Missions
Study our solar system and celestial bodies to determine origin and composition further, and compare them with exoplanets and other extrasolar celestial objects.
Transmission spectroscopy - look at these exoplanets’ atmospheres and examine the starlight filtered through them to learn about their chemical compositions
Examine physical and chemical properties of other stellar and planetary systems to provide insight into their formation
JWST
JWST Details:
- Largest and most powerful space telescope ever constructed
- International collaboration between NASA, ESA, CSA, and many scientists and engineers from around the world, from companies, countries, organizations, etc. (14 countries)
JWST
JWST Engineering Details:
Primary Mirror Size: 21.3 feet (6.5 meters)
Mirror Shape/Composition: 18 gold-plated hexagonal individually deployable segments
Sunshield: Five-layer deployable sunshield the size of a tennis court
Instruments: Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and Near-Infrared Imager and Slitless Spectrograph (NIRISS) with Fine Guidance Sensor (FGS)
Wavelengths: Visible Light, Near Infrared, Mid Infrared (0.6 - 28.5 micrometers)
Travel Distance: 1 million miles (1.5 million kilometers) from Earth
Location in Space: Orbiting the Sun around Lagrange point L2
