Luminosity is the energy that is being emitted/radiated by a star each second.

Brightness is the amount of energy that is emitted by a star each second that reaches an observer at a certain distance. The amount of energy radiated by a star that is received by an observer at a distance.

Light can be both but not a mixture. It can be a particle or a wave.

Light is a wave that is a mix of electric and magnetic energy, changing together. It can be seen as a wave in the ocean - reinforcing and calceling each other's effects in complex patters. And like ocean waves passing through a narrow inlet into a bay, light passing through an opening does not travel in a straight line, but spreads out.

Light is quantized; that is, it comes in discrete packets. Light is made of particles called PHOTONS - packets of energy/information. When photons enter your eye, they produce the sensation of light by striking your retina like microscopic bullets, releasing their energy and causing a chemical change in your photoreceptor cells.

wavelength vs. frequency

How are they related?

 Wavelength is the distance between two successive wave peaks or valleyes. Color is a representation of wavelength. Ex: Range of visible light: 7000 A - 4000 A (Red - Violet)

Frequency is the number of "cycles" per second that pass a given point. Measured in Hertz(Hz) where 1 Hz = 1 cycle/second.

Speed = wavelength (x) frequency

Long wavelength = Low frequency
Short wavelength = High frequency

Thermodynamic rules - an object behaves as a blackbody if it is:

1. an object that reflects NO light shining upon it.

2. an object that absorbs ALL light that falls upon it

3. an object that emits light as a result of its temperature only.

-blackbodies are not necessarily black

- stars are approximately blackbodies, so they can use this to measure the the size of stars in space based on their brightness.

A REFLECTING telescope uses a mirror to collect and focus light. A REFRACTING telescope uses a lens to collect and focus light.

Mirros are generally much less selective in the wavelengths of electromagnetic radiation they reflect, allowing much broader wavelength coverage with a single telescope.

Reflecting telescopes involve a curved mirror being able to focus light rays reflected from it. Glass can be polished to such a smoothness that the electromagnetic waves therefore can be brought together in sharp focus.

Refracting telescopes focus light by bending the rays. A lens that is just the right shape can collect light over the entire lens area and bend it so that it arrives at a focus behind the lens, creating an image. Bending occurs when light travels from air into water or glass. Light is bent b/c speed changes as it enters matter, generally slowing in denser material. This decrease in speed of light arises from its interaction with the atoms through which the electromagnetic waves move. (Think of right side of car driving into mud and the car curving to the right).

Problems with refracting telescopes: They are very heavy lenses that cannot be built on a large scale and they need to be very long to bring the light to a focus.

Advantages of reflectors: Larger diameter-more light-gathering ability. It can have many different focal points.

A spectrometer is a device for making a spectrum by spreading light out into its component wavelengths.

Photometers measure the total amount of light received from a celestial object over a chosen range of wavelengths.

Brightest stars visible=1st magn.
Next fainter stars=2nd magn.
Next fainter stars=3rd magn.
.......
Faintest stars visible=6th magn.

-A diff. of 5 magnitudes is a difference of 100 times in brightness. (Ex: 6th magn. stars are 100 times fainter than 1st magnitudes)

-The more negative #, the brighter the object.

The apparent magnitude of a star at a distance of 33 light years. It is related to the amount of energy the star is emitting (its luminosity).

Apparent Magnitude is the star's brightness as it appears from earth. Absolute magnitude is the apparent brightness of a star if viewed from a distance of 32.6 light years away.

Binary stars are two or more stars in a common orbit around each other.

-The stars are gravitationally bound together.

-The stars orbit a common center of mass.

-Can be complicated multiple star systems.

-The stars usually formed together as a multiple system (made at the same time, not a single star split apart).

Radius of the star is proportional to:

Luminosity of a star/surface temp of the star.

(Tells us the size of the star)

The apparent angular shift of a "nearby" object with respect to distant background objects due to the observer's own motion.

-The further away the star is, the smaller the shift (parallax).

OBAFGKM (Oh, Be A Fine Girl, Kiss Me.)

O-M=Hot-Cool

O 0-9 --- very few lines shown

B 0-9

A 0-9 --- mostly H lines shown

F 0-9

G 0-9 --- many metals shown

K 0-9                                 

M 0-9 --- metals and molecules