Untitled Flashcards Set

What is Alpha Centauri

-Our nearest Neighbors

a triple star system

Measuring distances to neighbors

-We use parallax

-Nearest neighbors are a handful of lightyears away 

Size of proxima centauri-

The closest star to the Earth is Proxima Centauri, 4.24 light years away

Making sense of distance-

If the sun were the size of a golf ball, in Snoqualmi,e alpha centauri would be a pea iAnchoragege Alaska

How long would the voyage take

-Even the fastest spacecraft would take a millennium to reach Alpha Centauri 

- space is very empty, stars are very far apart 

-As of now, it is closer to 165-155 AU away

-Proxima is 252,964 AU away

Itt would take 74,000 years to reach Proxima Centauri 

The nearest stars

-The only stars in the centauri system are within 5 light years 

-Centaury A and B form a binary star system

-Proxima Centauri orbits around them 

Which stars make up the solar neighborhood

-The solar neighborhood is the collection of stars within 15 light years of the sun

-only about 4 stars per 1000 cubic meters

-Most main sequence stars are faint, cold red dwarfs 

Stars like the sun are relatively rare 

This means we must search outside our planetary systems to find stuff

-The Milky Way is the diffuse band of light across the sky 

-The center and gas in the plane of the galaxy 

- The galactic bulge is a roughly spherical population

-Most bulge stars are older than those near the sun

-10 gyr old almost as old as the universe

-Nearly 200 billion stars in the Milky Way most of them are M-type bulge 

Measurement Tools of the Astronomer

Test Review

3

rd Law: P^2 = d^3

2

nd Law & 1st Law Inverse Square Law:

Light diminishes with

distance from source

Parallax view: the variation in angle that occurs

when viewing a nearby object from different

places.

• Importance of parallax: Danish astronomer

Tycho Brahe reasoned that the distance of

the object may be determined by measuring

the amount of parallax. A smaller parallax

angle meant the object was further away.

The apparent

change in the

location of an

object due to the

difference in

location of the

observer is called

parallax.

Their views

differ because

of a change in

position

relative to the

mountain

Because the parallax of the “star” was too small to

measure, Tycho knew that it had to be among the other

stars, thus disproving the ancient belief that the “heavens”

were fixed and unchangeable.

Brightness to Distance

❖ If you know the apparent brightness, you

know its luminosity (total energy output per

second)

❖ b = L /(4d

2

)

❖ Comparing to the Sun, can determine

distance to star

• Parallax is denoted by ‘p’.

• Distance (d) is measured in parsec.

• d = 1 parsec = the distance at which a star has a

parallax (p) of 1 arc second.

1 parsec = 3.26 light years.

Also d = 1/p

Closest star, Proxima centauri, p = 0.772 arc

seconds. Hence distance ‘d’ in parsec is

d = 1/p = 1/0.772 = 1.3 parsec = 4.2 light years

• Limitations on stellar parallax method

• 1. p = 0.01 arc seconds from Earth. So max.

distance = 100 parsecs

• 2. Hipparcos, p = 0.001 arc seconds. So max.

distance = 1000 parsecs.

• Other distance methods.

Limitation to using parallax

• Eventually, the parallax shift will no longer

be measurable.

• This is because the distance is too great for

the effect to be observed.

Electromagnetic Radiation

● There are only two long range forces

– Electromagnetism

– Gravity

● This is how we must observe the distant Universe

● Only now beginning to be able to observe

gravitational waves

● Most of our observations come from

electromagnetic radiation.

What Generates Electromagnetic Waves?

● Thermal radiation: Hot things glow.

● Heat causes atoms to rattle about in an object

● Atoms contain charged particles (electrons, protons)

● Accelerating charged particles emit electromagnetic

radiation.

Electromagnetic Radiation

● Electromagnetic radiation

from a source is in the form

of waves

● Both Electric and Magnetic

components

● Wave travels at speed of

light

Waves

Speed

wavelength

frequency

Electromagnetic Waves

● (speed) = (wavelength) x (frequency)

– But speed is fixed (all EM waves travel

at the speed of light)

– So given frequency, you can know the

wavelength and vice ver

● Higher frequency – more energy

● Higher amplitude – more energy

● But EM waves come in bundles (`photons')

with fixed amplitude

Electromagnetic Waves

● Light is one facet of the entire electromagnetic spectrum

● Our eyes have dedicated cells which are sensitive to

electromagnetic radiation in this range

● Eyes most sensitive to yellow light – this is where the sun

emits the peak amount of energy

Electromagnetic Waves

TV Antenna

VHF: ~200 MHz; wavelength~60”

UHF: ~575 MHz; wavelength~20”

15”

CB Radio Antenna

~27 MHz; wavelength~ 36 ft

~9'

Satellite TV dish

~12 GHz; wavelength ~9”

~4.5”

Inverse Square Law

● Electromagnetic (and most other

kinds) of radiation obey the Inverse-

Square Law

● Intensity of radiation (brightness)

falls off with the square of the

distance

– Doubling the distance to

something makes it appear

four times as dim (1⁄4 as bright)

– Tripling the distance makes it

appear nine times as dim (1/9

as bright)

– etc.

Kepler’s Breakthrough

• Kepler used Brahe’s data to develop three

laws that could be used to describe

planetary motion.

• All of the laws are based upon an

understanding of the ellipse.

After Tycho Brahe’s death,

Johannes Kepler (pictured here

with Tycho in the background)

used Tycho’s observations to

deduce the three laws of

planetary motion.

Planetary Motion and Orbits

• Kepler's first law states that

planets follow elliptical orbits,

with the Sun at one focus of

the ellipse. The figure below

illustrates Kepler's first law as

well as how an ellipse is

drawn.

• Newton was able to show

mathematically that, because

the force of gravity decreases

with the inverse square of the

distance, or 1/r

2

, closed orbits

must have the form of

ellipses or circles.

2014 Pearson Education, Inc.

The amount of elongation in a planet’s orbit is defined as its

orbital eccentricity. An orbital eccentricity of 0 is a perfect

circle while an eccentricity close to 1.0 is nearly a straight line.

In an elliptical orbit, the distance from a planet to the Sun

varies. The point in a planet’s orbit closest to the Sun is

called perihelion, and the point farthest from the Sun is

called aphelion.

Planetary Motion and Orbits

• Kepler's second law

relates speed and

distance. It states

that as a planet

moves in its orbit, it

sweeps out an

equal amount of

area in an equal

amount of time.

This is shown in the

figure below.

2014 Pearson Education, Inc.

KEPLER’S THREE LAWS OF PLANETARY MOTION

LAW #1. The orbit of a planet around the Sun is an ellipse with the

Sun at one focus.

Planetary Motion and Orbits

• Kepler's second law follows from the fact that

the force of gravity on a planet pulls directly

toward the Sun and, as a result, exerts zero

torque about the Sun.

• Since no torque acts on a planet, angular

momentum must be conserved.

• Newton was able to show that conservation of

angular momentum is equivalent to Kepler's

equal-area law.

2014 Pearson Education, Inc.

KEPLER’S THREE LAWS OF PLANETARY MOTION

LAW #2: A line joining the planet and the Sun sweeps out equal

areas in equal intervals of time.

Planet moves faster

in its orbit when

closer to the Sun.

Planet moves slower in

its orbit when farther

away from the Sun.

Planetary Motion and Orbits

• Kepler's third law relates the distance of a planet

from the Sun cubed and its orbital period

squared are proportional to one another, the

time it takes for the planet to complete one orbit.

• Simplified equation p^2 = d^3 – period squared

= distance from orbiting object cubed

2014 Pearson Education, Inc.

KEPLER’S THREE LAWS OF PLANETARY MOTION

LAW #3: The square of a planet’s sidereal period around the Sun is

directly proportional to the cube of its semi-major axis.

This law relates the amount of time for the planet to complete one orbit

around the Sun to the planet’s average distance from the Sun.

If we measure the orbital periods (P) in years and distances (a) in

astronomical units, then the law mathematically can be written as P2 = a3

.

Our Solar Neighborhood

❖ Our closest star other than the Sun – Proxima Centauri in the

Alpha Centauri triple-star complex – approximately l.y.

❖ Barnard’s Star next closest star farther out of the Centauri complex

Keplers first law tells us what?

Keplers second law tells us what about planetary orbit?

What does parsec tell you about a star?

What is an AU? 

Which types of light have more energy than visual light?

Electromagnetic radiation includes visible light as well as other types of radiation like radio waves, microwaves, and X-rays

All electromagnetic radiation travels at the speed of light (about 3 x 10^8 m/s) in vacuum, regardless of its frequency

The energy of electromagnetic radiation is directly proportional to its frequency - higher frequency means higher energy

Different parts of the electromagnetic spectrum have different uses and effects, from radio communications to medical imaging to heating food

Compare the parallax angles - the star with the larger parallax angle is closer to Earth

Step by step explainer

Parallax angle is the apparent change in position of a star when viewed from different points in Earth's orbit

The larger the parallax angle, the closer the star is to Earth

Star B has a parallax angle of 0.0037 arcseconds, which is larger than Star A's 0.0025 arcseconds

Therefore, Star B must be closer to Earth

Radio- Really

Microwave- Mad

Infrared- Insects 

Visable light- Violate

Ultraviolet- Urchin

X Ray- Xylophones with

Gamma Ray- Gay Racoons