Astro 1010 - Exam 2 Study Guide

Scalars possess magnitude and a unit.
- Examples:
  - Mass (e.g., $5$ kg)
  - Time (e.g., $12$ seconds)
  - Speed (e.g., $15$ m/s)

Vectors possess magnitude, unit, and direction.
- Examples:
  - Displacement (e.g., $9$ miles to the west)
  - Velocity (e.g., $60$ miles/hour in the negative direction)
  - Acceleration (e.g., $10$ m/s $^2$ downward)

Linear acceleration: Speeding up or slowing down along a straight line.
Centripetal acceleration: Moving in a circle (direction of velocity changes).
Acceleration due to Earth's gravity: Approximately $10$ m/s $^2$ (downward). All objects accelerate at this rate as they fall, neglecting air resistance.

1st Law (Law of Inertia): Objects maintain constant velocity unless acted upon by an outside force.
2nd Law: $F = ma$ , where $F$ is force, $m$ is mass, and $a$ is acceleration.
3rd Law: For every force on one object, there's an equal and opposite reaction force on another object.
Law of Gravity: $F = G \frac{m<em>1 m</em>2}{r^2}$ , where every mass gravitationally attracts every other mass. The gravitational force decreases as the distance between them increases. $G$ is the gravitational constant, $m<em>1$ and $m</em>2$ are the masses of the two objects, and $r$ is the distance between their centers.

False statement.
Earth's gravity keeps the moon in orbit, proving gravity exists in space.
Astronauts in orbit experience weightlessness because they are constantly falling around the Earth, not because of a lack of gravity.

Caused by the moon's gravitational pull being stronger on the near side of the Earth than the far side.
Spring tide: Sun and moon work together to enhance tides (during new and full moon).
Neap tide: Sun and moon work against each other to decrease tides (during first and third quarter moon).

Conserved quantity for a spinning object.
Momentum cannot be created or destroyed for an object, only transferred to/from another object.

Wavelength: Distance from max-to-max or min-to-min.
Frequency: How many cycles a wave goes through in a given time interval. Measured in Hertz (Hz = 1/second).
Wave speed = wavelength x frequency
Wave energy increases with higher frequency.

In order of increasing energy and frequency / decreasing wavelength: radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma-rays.
Radio waves: low energy, low frequency, long wavelength.
Gamma-rays: high energy, high frequency, short wavelength.
All are forms of light; visible light is only special because humans use it to see.
The speed of light is constant in a vacuum, and nothing can go faster than the speed of light in a vacuum. In non-vacuum, light travels more slowly. How much light is slowed down in a transparent material is defined by its index of refraction, $n$ ( $n = c/v$ ), where $c$ is the speed of light in a vacuum and $v$ is the speed of light in the material.

Mass energy: Energy contained in physical objects.
Kinetic energy: Energy of motion.
Thermal energy: Energy of heat.
Gravitational potential energy: Energy of objects lifted high above the ground.
Radiant (or radiative) energy: Energy of light.
Energy is conserved: It can be transformed or transferred, but the total amount of energy in the universe is constant.

Hotter objects emit the most intense light (brighter light) at shorter wavelengths and higher frequencies (more blue light) than cooler objects. However, a hotter object will emit more light at all wavelengths than a cooler one.

Emission: Hot matter converts thermal energy into radiant energy.
Absorption: Matter absorbs radiant energy of light and heats up.
Transmission: Light passes through matter (like a window). Light always refracts (changes speed and direction) when transmitted.
Reflection: Light bounces off matter (like a mirror).

Continuous spectra: Caused by a hot, dense object.
Emission spectra: Caused by a hot gas.
Absorption spectra: Caused by the light from a hot, dense object passing through a cool gas.

The chemical composition of an object.
Due to the Doppler Effect:
- Blueshift: Object is moving toward us.
- Redshift: Object is moving away from us.
- Spectral line broadening: Object is rotating.

Atomic number: Number of protons in an atom. Defines the element.
Atomic mass number: Number of protons + neutrons in an element. Defines the isotope.
Molecules: Multiple atoms held together by the attraction of positive and negative electric charges.
Just like light, matter has both wave-like and particle-like properties.

Curved lenses use refraction to gather light rays to a focal point.
Human eyes are lens-based; they focus light to the retina. The iris controls how much light enters the pupil and reaches the retina.
Digital cameras mimic the structure of the eye in many ways.

Angular resolution: Ability to see fine detail. Better angular resolution allows smaller angles to be seen.
- Larger telescopes have better angular resolution.
- Angular resolution can be improved with Adaptive Optics (AO) systems that compensate for atmospheric blurring (the "twinkle" of stars).
- Angular resolution can be improved with interferometry, in which multiple telescopes work together to produce a single image.
Light-gathering area: Ability to collect more light and therefore see fainter objects. Larger telescopes have better light-gathering power.
Magnification: Ability to make an image appear larger than normal. Depends on the size of the telescope + the eyepiece used.
Telescopes are either refracting (lens-based) or reflecting (mirror-based). Common reflecting telescope designs include the Cassegrain, Newtonian, and Nasmyth/Coude focus models.

Radio, visible, the near-infrared, and the near-ultraviolet can pass through Earth's atmosphere and reach the ground. Most of the infrared, most of the ultraviolet, gamma-rays, microwaves, and x-rays are absorbed or scattered as they pass through Earth's atmosphere; we need space telescopes to make observations at these wavelengths.

Radio: Arecibo and Greenbank
Infrared: SOFIA and James Webb
Visible and ultraviolet: Hubble
X-rays: Chandra and XMM-Newton
Satellite TV dishes are miniature radio telescopes.
Other than light, astronomers observe gravity waves in addition to particles such as neutrinos and cosmic rays.