Astronomy Chapter 1-5 Definitions

Midterm 1

Inter Stellar Media (IMS)

The matter that exists in the space between star systems in a galaxy, consisting of gas, dust, cosmic rays, and magnetic fields.

Large-scale structures

The observable ‘organization’ of galaxies.

Bow Shock

The observable process of particles slamming into the ISM.

Speed of light, c

300,000 Km/s

Baryonic matter

all the ‘tangible stuff’ in the universe. About 4% of the universe.

Dark matter

Makes up 22% of the universe. Responsible for the expansion of the universe.

Dark energy

Makes up 70% of the universe. Responsible for the expansion of the universe.

Astronomical unit, AU

Average distance from the Earth to the Sun. 1.496 X 10^8 km.

Light Year, ly

The distance light travels in a years time. 64,000 AU

Parsec, pc

3.26 ly

Asterism

The patterns (stick figures) on the sky.

Constellation

One of the 88 (unequal) regions of the sky. Any star within the boundary of a constellation belongs to said constellation.

Angular size

The angle an object subtends (spans) across the sky. Degrees.

Arcminute, arcmin, ‘

One degree = 60 arcminutes.

Arcsecond, arcsec, “

One arcminute = 60 arcseconds

Parallax

The apparent shift of an object relative to the background

Stellar parallax (p)

½ the total shift of a parallax.

Angular separation on Sky (equation)

= Physical separation / distance

Stellar parallax (equation)

1 / distance

Distance (equation)

= 1 / stellar parallax

The Earths angle of inclination is…

23 ½ degrees from vertical.

Precession

The wobble of the Earths axis over long periods of time.

Mean solar day

(what we’re used to) 24:00:00. Average amount of time between astronomical noon.

Sidereal Day

The amount of time it takes the Earth to spin once on its rotation axis. 23:56:00

The Earth moves ___ degrees in its orbit per day.

1 degree

The celestial sphere

An imaginary sphere in the sky, which the stars lie on.

Equinoxes

The points where the ecliptic & celestial equator intersect.

Vernal Equinox

The equinox where the Sun is travelling northwards (March 21)

Autumnal Equinox

The equinox where the Sun is travelling southwards (Sept 21)

Summer Solstice

The point where the ecliptic is the farthest north of the celestial equator. (june 21)

Winter Solstice

The point where the ecliptic is the farthest south of the celestial equator. (Dec 21)

Declination, dec

The celestial equivalent of latitude, measuring an object's angular distance north or south of the celestial equator. Measured in degrees.

Right Ascension, RA

The celestial equivalent to longitude, measured in time.

Circumpolar Stars

Stars that never rise nor set.

Magnitude Scale

Six brightness groups, from 1-6, brightest to dimmest.

Apparent visual magnitude, m

Stellar brightness expressed in the magnitude scale.

Flux

A measure of the light energy from a star that hits one square metre in one second.

Diffraction

Light will spread out like a wave as it passed through a narrow opening.

Blackbody Radiation

The radiation emitted by an opaque object.

Wave-particle Duality

The way in which light acts like both a wave and a particle depending on the situation.

Light is referred to as a ___ wave

Electromagnetic

Atmospheric window

The wavelength region where our atmosphere is transparent 

Primary lens

The large lens where the light comes into in a refracting telescope.

Eyepiece lens

The second lens on a refracting (or any) telescope.

Focal length

The distance between a lens and its focus.

Chromatic aberation

Lenses focus light of different wavelengths at slightly different spots, resulting in blur.

Charge-coupled devices (CCD’s)

A better newer alternative to using film in telescopes.

In active optics…

the shape of the mirror is continuously modified to compensate changes in the mirror shape due to gravity, thermal effects, etc.

In adaptive optics…

motorized supports adjust the shape of a mirror in the light-p[ath on much shorter timescales (thousnads of times a second)

Perfect blackbody

an object which absorbs all wavelengths of EM radiation.

Stefan-Boltzmann Law

the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature

Rules for atoms (theres four):

1. Electrons can only occupy certain specific locations (or states)

2. Each location can only have a limited number of electrons

3. An e^- at a specific location always has a specific energy. Since only specific locations are allowed, only specific e^- energies are allowed

4. An e^- can jump from one location to another only by gaining or losing a specific amount of energy

Balmer Series

For hydrogen, when an e- jumps levels and gives-off or absorbs photons corresponding to visible light, the energy level jumps are called this

The H_a transition corresponds with ___ light

green

the 3 notes on hydrogen atoms:

1. Absorption is only possible if the photon has exactly the rigfht amount of energy

2. Emitted photons have energy equal to exactly the energy difference between the final and the initial e^- levels. 

3. Each atom only has its own unique arrangement of energy levels, therefore each atom will only emit or absorb photons with distinct energies (wavelengths).

Emission line spectra

When e^- in an atom jump from HIGH energy to LOW, they spit out photons.

Absorption line spectra

When e^- in atoms jump from LOW energy to HIGH, they absorb photons.

Kirchhoff’s 3 Laws

1. A hot object, or a hot dense gas produces a continuous spectrum

2. A low density gas in front of a hotter source of continuous emission produces an absorption line spectrum.

3. A hot gas of low density gas produces an emission line spectrum.

The photosphere

the visible surface of the sun

Random Walk

The seemingly random movement of a photon moving from the centre of the sun to the outside, although random, it is moving towards the outside gradually and surely. This process takes millions of years, although light moves really fast, the gradual drift takes a long time.

Convection

Gas rising and sinking in the Sun

Redshift

If the wavelength is longer than expected

Blue shift

If the wavelength is shorter than expected

Radial velocity

Velocity along our line of sight

Proper motion

Motion perpendicular to our line of sight