UNIT 5: Astronomy
➢ Comet - loose collections of ices, dust, and small
rocky particles that originate in the outer reaches of
the solar system
➢ Asteroids and meteoroids - composed of rocky
and/or metallic material with compositions somewhat
like the terrestrial planets.
◦ small bodies (planetesimals) remaining from the
formation of the solar system, making them about
4.6 billion years old
◦ They are distinguished according to size:
▪ Asteroids are larger than 100 meters in
diameter
▪ Meteoroids have diameters less than 100
meters.
➢ Venus - brightest planet in the sky, has a thick, heavy
atmosphere composed of 97 percent carbon dioxide,
a surface of relatively subdued plains and inactive
volcanic features, a surface atmospheric pressure 90
times that of Earth’s, and surface temperatures of
475° C (900° F)
◦ rotates in the opposite direction of the other
planets (retrograde motion) at an agonizingly slow
pace
◦ composition of the Venusian interior is probably
similar to Earth’s.
◦ Venus’ weak magnetic field means its internal
dynamics must be very different. Mantle
convection is thought to operate on Venus, but
the processes of plate tectonics, which recycle
rigid lithosphere, do not appear to have
contributed to the present Venusian topography
➢ Stellar evolution
we can learn a great deal of information about the
relationships among the sizes, colors, and
temperatures of star
➢ Titan – Saturn’s Moon
◦ are the only satellites in the solar system known
to have substantial atmospheres.
➢ Evidence for an expanding universe came from the
study of red shifts in the spectra of galaxies. Edwin
Hubble concluded that the observed red shifts, later
called cosmological red shifts, were the result of the
expansion of space. This evidence strongly supports
the big bang model of an expanded universe. One
question that remains is whether the universe will
expand forever or gravitationally contract in the “big
crunch
➢ Impact crater - Depressions that are the result of
collisions with bodies such as asteroids and comets.
➢ Orion nebula - a well-known emission nebula that is
bright enough to be seen by the naked eye
◦ It is located in the constellation Orion in the sword
of the hunter.
➢ Chromosphere - The first layer of the solar
atmosphere found directly above the photosphere
➢ H-R Diagram - Einar Hertzsprung and Henry Russell
independently studied the relationship between the
true brightness (absolute magnitude) of stars and
their respective temperatures. Their work resulted in
the development of a graph, called a Hertzsprung–
Russell diagram (H-R diagram), that employs these
intrinsic stellar properties. By studying H-R diagrams,
➢ Hipparchus (2nd century B.C.) - Probably the
greatest of the early Greek astronomers
◦ best known for his star catalogue.
◦ determined the location of almost 850 stars,
which he divided into six groups according to their
brightness. (This system is still used today.)
◦ Measured the length of the year to within minutes
of the modern value and developed a method for
predicting the times of lunar eclipses to within a
few hours
➢ Constellations – 5,000 years ago people began
naming the configurations of stars, called
constellations, in honor of mythological characters or
great heroes.
◦ Today, 88 constellations are recognized that
divide the sky into units
➢ Cosmologist - a scientist who studies the field of
cosmology,which is the branch of astronomy and
physicsthat focuses on understanding the largescalestructure, origin, evolution, and ultimate fate
ofthe universe.
➢ Spectroscopy - Study of spectra
◦ Types of galaxies
▪ Spiral
▪ Elliptical
▪ Irregular
➢ The extremely narrow band of electromagnetic
radiation we can see (which is labeled as visible light)
is sometimes referred to as white light
◦ White light consists of an array ofwaves having
various wavelengths, a fact easily demonstrated
with a prism.
➢ Earth’s rotation can be measured in two ways, making
two kinds of days.
◦ Mean solar day - timeinterval from one noon to
the next,which averages about24 hours.
◦ Sidereal day - the time it takesfor Earth to make
one complete rotation with respect to a star other
than the Sun, a period of 23 hours, 56
minutes,and 4 seconds.
➢ Kuiper Belt - Named in honor of astronomer Gerald
Kuiper, who predicted its existence, the
◦ hosts comets that orbit in the outer solar system,
beyond Neptune.
The face of the moon ➢ Jovian planet - The Jupiter-like planets: Jupiter,
Saturn, Uranus, and Neptune. These planets have
relatively low densities
◦ VS Terrestrial Planets are categorized by:
▪ Location
▪ Size
▪ Density
➢ Jovian vs Terrestrial Planet Atmosphere
▪ differ with temperature and gravity
➢ Ecliptic - The yearly path of the Sun plotted against
the background of stars
➢ Galaxies – collections of interstellar matter, stars, and
stellar remnants that are gravitationally bound
➢ Oort Cloud - Named for Dutch astronomer Jan Oort
◦ consists of comets that are distributed in all
directions from the Sun, forming a spherical shell
around the solar system
➢ Three Main types of Bright Nebulae
◦ Emission
◦ Reflection
◦ Planetary
➢ Two Types of Terrain of Lunar Surface
◦ Dark Lowlands or Maria - appeared smooth,
resembling seas on Earth
▪ The Apollo 11 mission showed conclusively
that the maria are exceedingly smooth plains
composed of basaltic lavas.
▪ These vast plains are strongly concentrated
on the side of the Moon facing Earth and
cover about 16 percent of the lunar surface
◦ Highly Cratered Highlands or Terrae- resemble
Earth’s ontinents, so the first observers dubbed
them terrae (Latin for “land”).
▪ now generally referred to as the lunar
highlands because they are elevated several
kilometers above the maria.
▪ Rocks retrieved from the highlands are
mainly breccias, pulverized by massive
bombardment early in the Moon’s history.
◦ The arrangement of terrae and maria result in the
legendary “face” of the “man in the moon
➢ Solar Prominence - a large, bright feature extending
outward from the Sun's surface.
◦ anchored to the Sun's surface in the photosphere,
and extend outwards into the Sun's hot outer
atmosphere, called the corona.
➢ Solar Flare - brief outbursts that normally last an hour
or so and appear as a sudden brightening of the
region above a sunspot cluster.