AS103 Astronomy Exam 2

Planets’ orbits are

elliptical with the sun at a focus

The line between a planet and the sun sweeps out

equal areas in equal times

A complete orbit has P^2 = a^3, where P and a represent

sidereal orbital motion (yr) and semi major axis (Au) (conservation of angular momentum)

Newton’s first law

an object’s velocity will remain constant if there is no net external force acting on it

Newton’s second law: the acceleration of, mass of, and net force on an object are related as (equation) 

acceleration = net force / mass (F = ma)

Newton’s third law

the action and reaction forces between two bodies are equal in magnitude and opposite in direction. ΣF12 = -F21

Why do we say that an object traveling at constant speed on a circle is accelerated, even though its speed is not changing?

its direction of motion is changing. acceleration is a change in velocity and velocity is speed and direction

SB law says

total emission is proportional to T^4

Wien’s law says

different temperatures peaks at a wavelength is inversely proportional to the temperature

What is special about the Kelvin/absolute scale?

kelvin has zero temperature at minimum molecular kinetic energy. As cold as you can get. Energy is proportional to temperature. (more convenient)

What is conservation of energy

initial energy = final energy

Equation that relates initial and final energy of system (e- jumps from level 3 to level 1)

E1 + E = E3

Why is it possible to use the emission/absorption spectra of atoms to identify what element the atoms are?

the spectra (the photons) are unique to each element or chemical compound

What is the biggest obstacle to Earth-bound viewing in astronomy?

the atmosphere

Why are telescopes placed in high locations?

to get above some of the atmosphere. (less absorption)

Why are telescopes placed in remote locations?

darker, less light pollution (reflection)

What are two main types of telescope mounts

Altitude-azimuth, equatorial

How is alt-az aligned

zenith aligned

How is equatorial mount aligned

polar aligned

Which mount can carry the most weight

altitude-azimuth

Which mount is easier to use for taking pictures

equatorial

Rank eye, photo film, CCD based on sensitivity, linearity, data analysis

poor: eye, good: film, excellent: CCD

If you increase the diameter of telescope 3 times, by what factor does the image brightness change

9. B α D^2 … B’/B = (3D)^2 / (D)^2 = 9

If you increase the diameter of telescope 3 times, by what factor does the image resolution change

3. R α D … R’/R = 3D/D = 3

Rank the importance of magnification, brightness, and resolution

brightness=1, resolution=2, magnification=3

Is magnification improved by a larger diameter?

no

Is brightness improved by a larger diameter?

yes

Is resolution improved by a larger diameter?

yes

Mathematical relation to diameter (magnification)

none (D^0)

Mathematical relation to diameter (brightness)

D^2

Mathematical relation to diameter (resolution)

D^1

Which telescope (reflector or refractor) performs better with construction

reflector

Which telescope (reflector or refractor) performs better with spherical aberration

they perform the same

Which telescope (reflector or refractor) performs better with chromatic aberration

reflector

Which telescope (reflector or refractor) performs better with atmospheric transmission

they perform the same (relates to location)

Which telescope (reflector or refractor) performs better with light pollution

they perform the same (relates to location)
equation relating wave speed (v), frequency (f), and wavelength (lambda)?

Why do we sometimes speak of light as rays and sometimes as "electromagnetic waves"?

they can behave as particle and have magnetic field. Light travels in a straight line

Why do we have to use the absolute temp scale in describing blackbody radiation

because this scale is based on thermal energy

What are the two processes used by lenses and mirrors to focus light and create an image?

reflect and refract

What countermeasures can we employ against things that make for poor viewing

high, dry, and dark places

parts of a wave diagram

Electromagnetic spectrum diagram

blackbody diagram

photon emission/absorption diagram

equal areas equal times diagram

object traveling around sun diagram

object traveling in a circle diagram

diagram of refractor

diagram of reflector