|
Ch. |
|
Truth
|
| 1 |
Space is full of material.
|
Space is relatively empty.
|
| 1 |
You cannot add (5 x 107) +
(6 x 108).
|
Each part is a number, so
the two parts can certainly be added. To do so, write each term
so that all terms have the same exponent. |
| 1 |
We understand most of what
there is to know about the Universe. |
We have a lot to learn.
|
| 2
|
The equant is at the center
of the deferent. |
The equant is part of a
Ptolemaic Universe and is on the other side of the center of
the deferent (a circle) from the Earth. |
| 2 |
Copernicus knew about ellipses.
|
Everything in Copernicus's
ideas was circular. |
| 2 |
Copernicus's explanation
for retrograde motion works only for the outer planets. |
It works for the inner planets
too. |
| 3
|
Kepler's law for moons around
a planet has the same constant as for planets around the Sun.
|
Newton derived the form
of Kepler's law that includes the mass of the central object;
the constant relating period squared and distance cubed includes
this mass, so it depends on what the central object is. |
| 3 |
The relation between period
and distance for a planet's moons doesn't tell us anything special.
|
The relation between period
and distance for a planet's moons gives us the planet's mass.
|
| 4
|
All radiation is harmful.
|
Radiation includes ordinary
light. |
| 4 |
Spelling: infared |
Spelling: infrared |
| 4 |
Spelling: Kirchoff |
Spelling: Kirchhoff |
| 4 |
Spelling: absorbtion |
Spelling: absorption |
| 4 |
Spelling: lense |
Spelling: lens |
| 4 |
Telescopes are mostly used
to magnify things. |
Telescopes are mostly used
to collect light, so we can view fainter things. |
| 5
|
The Hubble Space Telescope
takes images only in visible light. |
Hubble is sensitive in the
ultraviolet and infrared. |
| 5 |
X-rays and radioactivity
have always been known. |
Roentgen discovered x-rays.
Becquerel discovered radioactivity. Marie Curie isolated new,
strongly radioactive elements. |
| 6
|
Twinkling results from stars
changing in brightness. |
Twinkling is caused in the
Earth's atmosphere. |
| 6 |
Polaris is the brightest
star in the sky. |
Polaris is not a particularly
bright star; it is merely easy to find and at a key location.
|
| 6 |
Changes in the Earth's distance
from the Sun causes the seasons. |
The seasons are caused by
the tilt of the Earth's axis, and the Earth's distance from
the Sun is irrelevant. |
| 6 |
A set of stars is a constellation.
|
Constellations are regions
of the sky, including space between and past the stars we see.
|
| 6 |
The Sun is a convenient
timekeeper to help us observe the stars. |
Our watches use solar time,
which differs by 4 minutes a day from sidereal time. |
| 6 |
The Moon is only up at night.
|
The Moon is often up in
the daytime. |
| 7
|
The dark side of the Moon
faces away from us. |
The dark side of the Moon
is the side away from the Sun, and it faces us at new Moon.
Do not confuse "dark side" with "far side." |
| 7 |
Small rocky planets are
found close to the main star of a solar system and gas giants
beyond. |
The discovery of giant planets
close in to distant stars has forced us to rethink our ideas.
|
| 7 |
All planets rotate in the
same direction. |
Three planets rotate backward
with respect to the other planets and to the sense of their
orbital motion. |
| 7 |
Most of the known planets
are in our solar system. |
Far more planets are known
outside of our solar system than inside. |
| 8
|
The tidal force is the gravitational
force. |
The tidal force is the difference
between the gravitational force at one place and the gravitational
force at another place. |
| 8 |
The tidal force varies with
the square of the distance. |
The tidal force varies with
the cube of the distance. |
| 8 |
The high tide on Earth is
below the Moon. |
High tides occur both on
the side of Earth facing the Moon and on the opposite side.
|
| 8 |
Spring tides occur in the
spring. |
"Spring" means to spring
up, and spring tides occur each month. |
| 8 |
Only the Moon causes tides.
|
The Sun also causes tides
on Earth, but they are weaker than tides caused by the Moon.
|
| 8 |
The ozone hole is permanent.
|
The ozone hole forms over
the south pole in its springtime, lasts a couple of months,
and then disappears. |
| 9
|
The Moon is too far away
to analyze its composition. |
The Moon is made out of
rock, with composition discovered by the Apollo missions. |
| 9 |
We can see all parts of
the Moon from Earth. |
Only about 5/8 of the Moon
ever faces us. |
| 9 |
The Moon's far side is always
dark. |
The Moon's "far side" faces
away from us but is sometimes dark and sometimes light. The
dark side is merely the face that is not being hit by sunlight.
|
| 10
|
Mercury is all very hot.
|
Some parts of Mercury are
permanently shaded and are cold. Water ice may even be present.
|
| 10 |
We know a lot about Mercury.
|
We don't even know what
half of it looks like. |
| 11
|
Venus's atmosphere is like
Earth's. |
Venus is hot enough to melt
lead and has 100 times the Earth's surface pressure. |
| 11 |
Spacecraft discovered that
Venus is very hot. |
We know from radio waves
received on Earth that Venus is very hot. |
| 11 |
Spacecraft discovered that
Venus's atmosphere is 96 percent carbon dioxide. |
We learned the composition
of Venus's atmosphere from Earth. |
| 11 |
Radar from spacecraft can
study the clouds. |
Radar at the wavelengths
used at Venus penetrates the clouds and studies only the surface,
unlike terrestrial weather radar. |
| 12
|
Mars is not much farther
than the Moon, so astronauts can go there without much more
difficulty than the Apollo program. |
Mars is, even at its closest,
200 times farther than the Moon, so it is much more difficult
to get to. |
| 12 |
We are certain that life
never arose on Mars. |
Most scientists agree that
no signs of life have been found, but the evidence for liquid
water on Mars leaves many hopeful. |
| 13
|
Jupiter's moons are hard
to see. |
Even binoculars or a very
small telescope can show moons orbiting Jupiter. |
| 13 |
Jupiter is much like Earth.
|
Jupiter dominates the Solar
System, and its size and mass give it many properties very different
from Earth's. |
| 13 |
Only Saturn has rings. |
Jupiter and, as we shall
see, Uranus and Neptune also have rings. |
| 14
|
The probe on Cassini will
go into Saturn's atmosphere. |
The probe on Cassini will
go into the atmosphere of Saturn's moon Titan. |
| 14 |
Saturn's rings are solid.
|
Saturn's rings are composed
of individual chunks of rock and ice. |
| 15
|
Uranus's rings have always
been known. |
Uranus's rings were discovered
only two decades ago. |
| 15 |
We have a lot of material
on Uranus and its moons. |
We've had only one flyby:
Voyager 2. We couldn't image even half of each moon. |
| 16
|
Neptune's Great Dark Spot
is a permanent feature. |
Neptune's Great Dark Spot,
discovered by Voyager 2, disappeared a few years later. |
| 16 |
Neptune is so cold that
it is uninteresting. |
Neptune has more weather
than Uranus; Triton is a fascinating moon. |
| 17
|
Pluto is the 9th planet
because it always orbits outside Neptune. |
Pluto is the 9th planet
because the semimajor axis of Pluto's orbit is larger than that
of Neptune. |
| 17 |
Pluto is a big planet, like
the other outer planets. |
Pluto is much smaller than
Earth; so small that its planethood has been challenged. |
| 17 |
Pluto was discovered because
of its effect on the orbit of Neptune, then the outermost planet
known. |
Tombaugh's search was based
on Uranus, since Neptune's orbit was not sufficiently well known.
In any case, Pluto has so little mass that its effect on either
of those bodies is not measurable. |
| 18
|
The planets discovered around
other stars can be photographed. |
It will be decades before
we can image these planets. |
| 18 |
Other solar systems also
have small, rocky planets close in and Jupiter-like planets
in Jupiter-like orbits. |
Other solar systems often
have Jupiter-like planets very close in. |
| 19
|
The orbit of Halley's Comet
extends outward equally to either side of the Sun. |
Because the elliptical orbit
has the Sun at one focus, and because the focus is close to
one narrow end of the ellipse, a comet's orbit extends much
farther to one side. |
| 19 |
A comet's tail trails behind
the comet. |
Comet tails point away from
the Sun, even if they go ahead of the comet. |
| 20
|
Shooting stars are stars.
|
Shooting stars are interplanetary
dust burning up in our atmosphere. |
| 20 |
The asteroid belt is densely
packed. |
Distances between asteroids
are very great, unlike in the movies. |
| 20 |
The Kirkwood gaps have spacings
that are fractions of a planet's orbital radius. |
The Kirkwood gaps arise
at spacings that correspond to orbits that are simple fractions
(1/2, 1/3) of the period of Jupiter. |
| 20 |
Asteroids are not a hazard
for us on Earth. |
The odds are that asteroids
hit the Earth with some long-term (though rare) regularity and
do great damage. |
| 21
|
We know the best frequencies
at which to listen for messages from extraterrestrials. |
It is unclear that we can
correctly guess frequencies that unknown extraterrestrials might
choose. |
| 22
|
All parts of the Sun, as
seen from Earth, have the same spectrum. |
The photospheric spectrum
is in absorption and the chromospheric and coronal spectra are
in emission. |
| 22 |
The Sun has parts that are
solid. |
The Sun is gaseous throughout.
|
| 22 |
The Sun emits only yellow
light. |
The Sun emits radiation
all across the spectrum, with yellow-green as the strongest
color. |
| 22 |
The Sun shines because gas
is burning there. |
Burning is a chemical process,
while the Sun and stars shine by nuclear processes (fusion).
|
| 23
|
There are always sunspots
on the Sun. |
At solar minimum, there
may be weeks without sunspots. During the Maunder minimum, there
were decades without sunspots. |
| 23 |
Red spots on the edge of
the Sun are flares. |
Often these objects are
prominences, which are much cooler than flares. |
| 24
|
All stars are the same color.
|
The colors of stars show
their temperatures. |
| 24 |
All red things in the sky
are cool. |
Red stars are cool, since
we are seeing continuous radiation, but emission line sources
that show red Ha can be hot. |
| 24 |
Stars shine because of spectral
lines. |
Continuous radiation comes
mostly from the negative hydrogen ion. |
| 24 |
The Balmer series is a hydrogen
atom with electrons jumping to and from energy level 2. |
The Balmer series is the
set of spectral lines from hydrogen observed in the visible.
(The misconception actually describes the Bohr atom.) |
| 24 |
The Bohr atom has 5 levels.
|
The Bohr atom has an infinite
number of levels. |
| 25
|
A bright star is close to
us. |
It can be intrinsically
very dim but close. |
| 25 |
A dim star is far from us.
|
It can be intrinsically
bright but far. |
| 25 |
5 magnitudes is 100 times
brighter, so 10 magnitudes is 200 times. |
Multiply factors. 10 magnitudes
is 100 x 100 = 10,000 times brighter. |
| 25 |
Stars are fixed in the sky.
|
Many stars have measurable
proper motions. |
| 26
|
Most stars are single. |
Most stars are multiple.
|
| 26 |
All stars have the same
mass. |
For main-sequence stars,
stars of greater luminosities have greater masses. |
| 26 |
Stars are steady in brightness.
|
Many stars vary in brightness.
|
| 26 |
Stars are too close to bother
about if we want to learn about cosmology. |
Important cosmological measurements
depend on accurate knowledge of stars, such as Cepheid variables.
|
| 26 |
Stars are all made of the
same stuff. |
The proportions of the elements
are quite different in younger and older stars. |
| 27
|
Stars don't change and live
forever. |
Stars evolve from birth
to death. |
| 27 |
Stars follow the same evolutionary
path. |
Evolutionary tracks depend
on mass. |
| 27 |
Radioactivity has always
been known. |
Radioactivity was discovered
just over 100 years ago and was named by Marie Curie. |
| 27 |
Stars shine from the carbon
cycle. |
Stars, like the Sun, shine
from the proton-proton chain. |
| 27 |
Fe III is three-times-ionized
iron, etc. |
Fe III is twice-ionized
iron, etc. |
| 27 |
We can always feel high
temperatures. |
High temperatures mean fast-moving
particles, which we feel only if there are many of them. |
| 28
|
Planetary nebulae have to
do with solar systems. |
Planetary nebulae are gaseous
and have nothing to do with planets. |
| 28 |
White dwarfs and dwarfs
are the same. |
A white dwarf is the dead
hulk of a burned-out star and is found in the lower left of
the H-R diagram, while "dwarf" refers to a normal star on the
main sequence. |
| 28 |
Brighter stars are bigger.
|
Almost all stars are mere
points on images; brighter stars may appear bigger on film because
of effects of overexposure on the film. |
| 29
|
Stars are placid. |
Some stars explode violently.
|
| 29 |
Supernovae are exploding
single stars. |
Type I supernovae explode
because they are in binary systems and matter from a companion
flows onto a white dwarf. |
| 29 |
We get only radiation from
stars. |
Sometimes we get particles,
such as neutrinos or cosmic rays. |
| 30
|
Pulsars are stars that pulsate.
|
Although pulsation was briefly
considered, we now know that pulsars rotate rather than pulsate.
|
| 30 |
Pulsars have constant pulse
rates. |
Radio pulsars slow down;
x-ray pulsars speed up. |
| 30 |
Neutron stars are detected
only as pulsars. |
At least one non-pulsing
neutron star has been found. |
| 31
|
Black holes can't be seen
or detected. |
We can see x-rays and other
radiation emitted just outside the black hole, and we can also
detect gravitational effects. |
| 31 |
Black holes suck in matter,
as do vacuum cleaners. |
Black holes of millions
of solar masses don't have strong gravitational pull outside
their event horizons. |
| 31 |
Einstein's general theory
of relativity set the speed of light as a limit. |
Einstein's general theory
is a theory of gravity; the speed of light as a limit was set
by the special theory 10 years earlier. |
| 31 |
Black holes and black bodies
are the same. |
A black body is any radiating
body whose emission follows Planck's law. Black holes are the
result of strong gravity, as described here. |
| 32
|
We can see the center of
our galaxy. |
The center of our galaxy
is hidden from visible light by dust. |
| 32 |
We can measure directly
how far away the center of our galaxy is. |
We must use indirect methods
to detect the size of our galaxy since we can only measure parallaxes
for less than 1000 light years. |
| 32 |
Galaxies have spiral arms
because they spin and draw out material. |
The spiral arms we see are
probably illusions caused by density waves. |
| 33
|
Interstellar space is invisible.
|
Gas and dust can prevent
us from seeing far through the interstellar space. |
| 33 |
The Balmer series is the
strongest set of spectral lines of hydrogen. |
21-cm
radiation, from a split in the lowest energy level of hydrogen,
arises from a more fundamental state of hydrogen than the Balmer
series. The Lyman series lines are very strong, though cannot
be seen through our atmosphere. |
| 33 |
Hydrogen molecules in space
are easy to detect. |
Only from above the atmosphere
have we been able to study hydrogen molecules. |
| 34
|
Spiral nebulae are in our
Galaxy. |
The "spiral nebulae" turn
out to be galaxies comparable to our own. |
| 34 |
Galaxies evolve along the
Hubble tuning-fork diagram. |
Once formed, in the absence
of interaction, galaxies retain their Hubble type. |
| 34 |
Ellipticals and spirals
formed at the same time. |
It seems that many ellipticals
formed from collisions of spirals. |
| 34 |
Galaxies are individual
in space. |
Most galaxies are in clusters.
|
| 34 |
We are limited in size of
telescopes by the need for the parts to be connected. |
Interferometers can have
parts scattered over the world or in space. |
| 35
|
The Universe is static.
|
The Universe is expanding.
|
| 35 |
The Universe expands unpredictably.
|
There is a simple relation
between velocity and distance. |
| 35 |
The Universe expands smoothly.
|
There are slight deviations
from uniform expansion caused by mass concentrations. |
| 35 |
We can readily measure distances.
|
It is hard to measure distances.
|
| 35 |
The Universe is mostly ordinary
matter. |
The Universe may be mostly
dark matter, which is invisible. |
| 35 |
An accelerating Universe
is the same as an expanding Universe. |
In an accelerating Universe,
distant objects are receding more rapidly than in a uniformly
expanding Universe. |
| 36
|
Galaxies are the farthest
things in the Universe. |
Certain quasars are the
farthest things in the Universe. |
| 36 |
Quasars are farther than
galaxies. |
We now know of some galaxies
as far as many quasars. |
| 36 |
Quasars are like pulsars.
|
Quasars are events in the
centers of galaxies; pulsars are stellar. |
| 36 |
Sloan and 2dF map only the
positions of objects in the sky. |
Sloan and 2dF measure redshifts,
giving distances, in addition to positions. |
| 36 |
Objects at the same distance
can have different redshifts. |
Essentially all astronomers
think that Hubble's law holds for both quasars and galaxies.
|
| 36 |
Apparent velocities of parts
of quasars indicate motions faster than the speed of light,
violating Einstein's special theory of relativity. |
The apparent superluminal
velocities can be explained as projection effects in matter
moving close to, but less than, the speed of light. |
| 37
|
Galaxies and clusters of
galaxies expand as the Universe expands. |
Galaxies and clusters of
galaxies remain the same size, though they grow farther away
from each other. |
| 37 |
It is obvious that matter
cannot be created out of nothing. |
We have been able to rule
out the steady-state theory, but the rate invoked for the creation
of matter is too low to rule out straightforwardly. |
| 37 |
The big-bang theory is doubted
by a significant number of astronomers. |
Essentially all astronomers
have concluded that the big-bang theory is valid. Only a handful
of astronomers are not convinced. |
| 37 |
We can see back to the big
bang. |
The Universe was dense and
opaque about 300,000 years after the big bang, and we cannot
see further back in any part of the spectrum. |
| 37 |
The cosmic background radiation
(CBR) is uniform. |
The CBR has a dipole anistropy,
which shows on the largest scale, and, when that is removed,
shows small-scale anistropies. |
| 37 |
The CBR's Planck curve shows
two or three peaks. |
All Planck curves have only
one peak; the two or three peaks associated with the CBR have
to do with the graph of fluctuation size. |
| 38
|
The vertical axis of the
graph of a Planck curve is temperature. |
The vertical axis is intensity,
or energy given off, while the horizontal axis is wavelength.
Each temperature corresponds to a different Planck curve on
these axes. |
| 38 |
We know the full list of
particles that make up our Universe. |
We are discovering new particles
all the time in particle accelerators. |
| 38 |
Protons and neutrons are
the most fundamental particles. |
Protons and neutrons are
made of quarks, as are all other "baryons." |
| 38 |
Electrons are made of quarks.
|
Electrons are fundamental
particles, and along with muons and tau particles, they are
called "leptons." |
| 38 |
The elements always existed.
|
Hydrogen and helium were
formed right after the big bang, and other elements were formed
later in stars or supernovae. |
| 38 |
The Universe has always
been expanding at about its current rate. |
Most cosmologists think
that the Universe underwent a period of inflation. |