Science
ademola
Oct26_stars_planets.pptxWhere we left off last time…..
Star charts useful for observing sky for different latitudes,
time of year, time of day, but…..
Completely misleading as to what you are actually observing
This is due to distance.
Distances to things in space are enormous- need a way to cope
For distances from earth to sun and other planets- hundreds of
million or a few billion miles, we defined the
astronomical unit. Earth is 1 A.U. from the sun
For the trillions or quadrillions of miles to the stars, we need something
better……………… the light year
Speed of light (or any electromagnetic radiation)
is the fastest thing in the universe. But its not
instantaneous.
Point a laser beam at the moon. It would take 1 ¼ second to get
there.
Light travels at 186,000 miles per second (300,000 km/sec)
Point a laser beam at the sun. It would take 8 minutes to get there.
Send a radio signal (same physics as light) to our spacecraft passing
Pluto. It takes about 3 hours to get there. Compare with our
fastest spacecraft, called New Horizons, going 16 km/second
took 10 years to get to Pluto.
(at that speed how long would it have taken to get to the moon?)
Definition of a light year
A light year is the distance that a beam of light can cover in 1 year.
How far is that?
Distance = rate x time
rate (=speed): 300,000 km/sec
time : 31 million (=31,000,000) seconds/year
1 light year = 31,000,000 times 300,000 =
= 3.1 x 107 times 3 x 105
= 9.3 x 1012 km 5.9 trillion miles
Closest star is 4.2 light years away (about 25 trillion miles)
When astronomers began to realize how far away stars were
The Dutch astronomer Christiaan Huygens in 1690, who by assuming our sun was like the stars and estimated the sun appeared 30,000 brighter, hypothesized that the stars were about 30,000 further from us than the sun. He was off by a factor of 10-1000, but still it was a great first attempt. He wrote
How vast those Orbs must be, and how inconsiderable this Earth, the Theatre upon which all our mighty Designs, all our Navigations, and all our Wars are transacted, is when compared to them. A very fit consideration, and matter of Reflection, for those Kings and Princes who sacrifice the Lives of so many People, only to flatter their Ambition in being Masters of some pitiful corner of this small Spot.”
taken from The Cosmic Perspective by Jeff Bennett et al.
Our sun and the stars you see in context Artist conception of looking down on the Milky Way galaxy
One of about 1 billion stars in our galaxy (and there are about a trillion galaxies!)
Our nighttime sky lies within 1000 light years (within the small circle)
About 6 quadrillion miles (i.e. 1000 x 6 trillion)
About 125,000 light years
Lets take an Astronomical Tour:
What does it mean to say our sun is an average star?
What is a star?
How are they categorized?
See text: 27.2, and 27.3 (but a problem is they presume you’ve had
The physics class which coves earlier chapters)
Lets take an Astronomical Tour:
What does it mean to say our sun is an average star?
What is a star?
something that shines by its own light: A large
glowing ball of gas
How are they categorized?
By brightness, temperature and size
There is a problem with the word “brightness” however…….
Apparent vs. Intrinsic Brightness
Sun looks brighter but that’s only because its closer.
Apparent Brightness
Intrinsic brightness refers to what it would look like if we
viewed all stars at the same distance.
Luminosity: amount of energy produced by a star
Luminosity and Temperature and Color
Conveniently, they are all related!
What happens when you turn on an electric stove?
First, feel the warmth, but no color
Second, hotter, dull red
Finally, hottest, bright red/orange
Spectrum of Colors
warm
hottest
Nail being heated by propane torch
The color of a heated
glowing object can
tell you the temperature
Black Body Radiation
Things which feel warm,
but not yet
Red are “infra-red” Hotter than blue is “ultraviolet”
degrees
What’s our sun?
What’s our sun?
Can you see why our sun is called “ordinary”?
Note: Slightly misleading in that our sun is called a “yellow star”
Has to do with what our eyes perceive- we are more sensitive to yellow than blue
5500K
Its right in the middle
What’s wrong with this picture??
Light bulbs and artists in general use a backward scheme to
describe color!!! Its purely psychological- people think
of blue as “like ice” and fire is red. We rarely see
true “blue hot” on earth (welder’s torch perhaps)
(drives me personally nuts at hardware stores!)
Main Sequence of stars: Luminosity vs. temperature
G
K
M
F
A
B
O
Note the letters: how stars
Are formally classified
Our sun sits in the middle of
The main sequence
Two images of same graph
Main Sequence of stars: Luminosity vs. temperature
G
K
M
F
A
B
O
Massive and
100-1000 X brighter
than our sun. Least
common star type
Smaller and
100-1000X dimmer
than our sun. Most
common
S
Why do stars glow?
If enough mass of gaseous hydrogen and helium are concentrated
together- nuclear reactions (convert hydrogen and helium to other
elements) can occur to emit radiation
Our sun is a 4.5 billion year old hydrogen bomb!
What are hydrogen and helium?
Hydrogen: lightest and simplest element. Most common in
universe. On earth, its bonded to earth’s crust’s most common
element, oxygen to make H2O (water)
Helium: 2nd lightest, second simplest and 2nd most common.
Not very reactive
6 out of the magnificent 7 elements
1. Iron (Fe): Earth’s core, a little in the mantle and basalt
2. Silicon: 2nd most common in earth’s crust. Makes silica and
common in granitic magma
3. Oxygen: Most common in earth’s crust.
4. Carbon: Present in rocks and the atmosphere (more on that
in a couple of weeks)
5. Hydrogen: Lightest element.
Most common in the universe. Stuff of stars
6. Helium : 2nd lightest, 2nd most common in the universe
Sun is 75% hydrogen, 25% helium, a tiny trace of heavier
elements
One more to go in a couple of weeks (nitrogen)
What is a Solar System?
A solar system is a collection of objects that are gravitationally associated with (meaning they orbit) a star
In our case, the star is the sun.
What kind of objects?
Objects in the solar system
1. 1 sun
2. 8 major planets: What are they?
a. 4 inner, rocky, terrestrial planets
b. 4 outer, gas giants (or Jovian planets)
3. Dwarf planets
4. Satellites which revolve around the
planets our moon is a satellite of Earth
5. “Junk”- stuff which isn’t spherical
comets, meteors, asteroids
Size of objects in solar system: a model
Sun has by far away most of the mass. Planets are like left over debris.
Even smaller stuff: moons, asteroids, comets too small to show up
Major Planets
Objects that orbit (revolve around) a star
and do not shine
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune My very excellent mother just served us nachos
What kind of objects? We will define
shortly
Layout of the major planets
Remember we call this A.U: Astronomical Units. Earth = 1
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
4-12X Bigger than earth
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
Near Earth in size,
or smaller
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245 988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
A size gap between Earth and Neptune ?
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.554812834224598 8 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
Close to sun
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245 988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
Big planets are further away
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
Close to sun
means hotter
Mercury is .4 AU from sun
Venus is .7 AU from sun
Mars is 1.5 AU from sun
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245 988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Looks like two groups?
further away means colder
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Gap between Inner and Outer Solar system
A gap between Mars
And Jupiter? Asteroid belt
Jupiter’s large gravity may have
Prevented a large planet from forming
?
?
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Two Types of major planets
Rocky (like Earth)
Smaller, close to sun,
warmer
Terrestrial planets
Mercury
Venus
Earth
Mars
2. Big and gassy like Jupiter
Jovian planets. (Jove is synonym for Jupiter)
Far from sun. Cold.
Jupiter, Saturn, Uranus, Neptune
What does “warm” or “cold mean?
Can water be liquid?
Gas giants are way too cold for liquid surface water
Venus is too close to the sun too hot, oceans boiled away
Mars is probably slightly too far too cold, water and dry ice no liquid
Earth is just right for liquid water the “Goldilocks Zone”
How might the Habitable Zone change for different stars?
Different stellar luminosities different habitable zones
Like a dim fire, the low mass stars would be cooler so habitable
planets (i.e. to have liquid water on surface) would need to huddle closer
A bright (luminous) high mass star would push the habitable zone much further away
Is the only possible arrangement a solar system can have?
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Only two groupings for planets? They thought so… until 25 years ago.
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Most stars have their own planets- different from our solar system: called Exoplanets
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Exoplanets are turning out different than “our” planets!
0 0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (?)
0.38709893048128347 0.7232620320855615 1 1.5236631016042781 5.2027406417112303 9.5548128342245988 19.191109625668449 30.108957219251337 39.528877005347589 0.38256506741925367 0.94888679836939482 1 0.53261210410787085 11.209156475384132 9.4493571652555666 4.007369081216682 3.883035434305425 0.18030730636563186
relative distance from Sun
relative diameter
Whats a planet, exactly?
First: must be a sphere
There is a certain size which provides enough gravity to become
a sphere
Major planets are also big enough to clear their orbits. Smaller material
often orbits them- we call those satellites.
3rd category: Icy dwarf planets like Pluto
The moon
Pluto
Pluto is big enough to be round like a planet. But
smaller than our moon separate category
Probably are lots of Dwarf Planets (we’re not sure- most are beyond the orbit of Neptune) here are 5
Dwarf Planets and Icy Moons similar in composition. Jovian planets have many: here are 4 from Jupiter
These 4 objects were the first ever discovered with a
telescope. By Galileo in 1605-1610. The “Galilean Satellites” of Jupiter.
They (like the dwarf planets) are a mix of rock and ice
And if its not a sphere?
Either a rocky asteroid or icy comet
They are too small to acquire a spherical shape
In summary: know the vocabulary and the variations
Know the 6 types of objects in our solar system
(sun, 3 types of planets, moons, non-spherical objects)
and be able to distinguish and describe each.
2. Understand terminology describing motion of objects in
the solar system. What orbits what?
3. For planets- how do they vary amongst each other?
4. Appreciate the size of the solar system and distance to
the stars
5. Difference between exoplanets and “our” planets. Is our solar
system the only kind you can have….. No!
