A belt about 16° wide around the sky centered on the ecliptic, containing 12 constellations
Wien’s Law of Radiation
The wavelength, max, at which a blackbody emits the greatest amount of radiation is inversely proportional to its temperature (T). max =0.3/T
One half of the apparent change in the star’s angular position,
which is used to calculate the distance of the star.
The velocity of a star with respect to the sun
A stream of energetic electrically charged particles that flow out from the Sun.
The amount of the Sun’s energy that falls per second on Earth’s
outer atmosphere, about 1400 watts per square meter (126 watts per square foot). Changes in the solar constant might drastically change Earth’s climate and atmosphere.
Tremendous, short-lived, explosive outburst of light and material.
Bright cell that looks like rice grain the photosphere.
Coronal Mass Ejection
Most energetic eruption of material from the solar corona.
Elementary particles predicted to be produced in
nuclear reactions in the core.
Dark, relatively cool blotches in the bright photosphere.
Astronomical Unit (AU)
The astronomical unit (AU) is the average distance between
the Earth and the Sun, about 150 million km (93 million miles) (officially 149,597,870 km).
The changes that take place in stars as they age/ The life cycle of stars.
Birth of a star
1) Gravitational contraction of a cloud of gas and dust
2) Rise in interior temperature and pressure
3) Nuclear fusion
A superdense, gravitationally collapsed mass from which no light,
matter, or signal of any kind can escape.
An enormous collection of stars and gas and dust held together in space by the force of gravity.
Galaxies in which the clouds of gas and dust are much more dense.
A galaxy that has a relatively small brilliant nucleus with broad emission lines in its spectrum.
A galaxy with luminosity that can be explained as the composite of a collection of many individual stars.
A very energetic and distant active galactic nucleus that shows the largest redshift known
Radiograph shows two large patches emitting radio waves on opposite sides of a visible galaxy located between them.
The branch of science concerned with the origin, present structure, evolution, and the final destiny of the universe.
A galaxy’s velocity of recession (v) is directly proportional to its distance away from us (d). The formula is v=Hd where H is called the Hubble constant. The Hubble constant is very important because it gives the rate at which the galaxies are receding or the rate at which the universe is expanding. It is the basis for estimating the size and age of the universe.
On a sufficiently large scale, the universe is homogeneous and isotropic at any given time.
Theory for the formation of the solar system stating that all of the planets revolve around the Sun in the same direction and the orbits of all planets lie nearly in the ecliptic plane.
Irregular, rocky bodies that orbit the Sun, mostly between the orbits of Mars and Jupiter.
Wrote a book describing heliocentric model of planetary motions, which was published in 1543, the year he died.
First used a telescope for astronomical work and discovered the phases of Venus, advocate of the heliocentric model
Determined his three laws of planetary motion empirically from observational data.
Formulated the three fundamental laws of motion and the universal law of gravitation.
Described a geocentric view of the universe in the “Amagest” about A.D. 150
Observed and recorded planetary motions for almost 20 years, created a model of the solar system in which the Sun and Moon revolve around the Earth, and the other five planets revolve around the Sun
The electronic spectrum [from shortest wavelength (highest energy) to longest wavelength]
Gamma Rays, X-Rays, Ultraviolet Radiation, Visible Light, Infrared Radiation, Radio Waves
Wavelength = Speed of wave/ Frequency
Purpose of a spectograph
To separate and record the individual wavelengths in a beam of light.
The three advantages of using a radio telescope
1) It reveals radio sources
2) It shows radio sources that are hidden from sight behind interstellar dust clouds in the Milky Way galaxy, and it also works in cloudy weather and daytime
3) It shows radio sources that are located beyond our power of optical viewing.
How is a star’s spectrum formed?
Stars are blazing balls of gas where many kinds of atoms emit light of all colors. This light, emitted from the star’s surface, passes through the star’s outer atmosphere. There, atoms of each element absorb their characteristic wavelengths, so a pattern of dark lines crosses the continuous band of colors—the star’s spectrum
Why are the bright (dark) spectral lines of light emitted from (absorbed by) the atoms of an element unique to that element?
Each spectral line is light of a particular wavelength
emitted (or absorbed) by the atom when one of its electrons jumps between a higher and a lower energy level (orbit). Each element has its own unique set of allowed electron orbits, so each element has its own characteristic set of spectral lines.
Two windows (spectral ranges) in the Earth’s atmosphere for observational astronomy
Visible light and radio waves
The main advantages of giant telescopes for research
The superior light-gathering power and resolving power.
The two factors that are the most important in a telescope’s performance
The size and quality of the main mirror or lens (also a stable mount is essential.)
The advantage of sending telescopes up in a spacecraft
A spacecraft takes the telescope beyond the Earth’s obscuring atmosphere, and it is possible to observe gamma ray, X-ray, and ultraviolet sources that cannot be observed on the ground. There is no atmospheric blurring or radio interference, so a space telescope can work at is practical limit of resolving power
Characteristics of red giants
Red giants are relatively cool but luminous; hence, they must have a large surface area radiating energy.
Characteristics of white dwarfs
White dwarfs are relatively hot but faint; hence, they must have a small surface area radiating energy into space.
Three reasons why modern astronomers study the Sun
1) The Sun is a free, nonpolluting, almost inexhaustible source of present and potential future energy.
2) The Sun is the only star close enough to observe in detail, so astronomers use it to determine what other stars like.
3) Changes in the Sun’s energy output affect Earth’s climate, atmosphere, and weather, as well as power-transmission and communications systems.
Observation of the sunspot cycle
The sunspot cycle is watched carefully from Earth as an indicator of solar activity. The sun is most active, with greatest outbursts of energy and radiation, during the years when sunspots are most numerous. It is least active in the years of sunspot minimums.
Four ways that a flare and unusually big blasts of solar wind can affect the Earth’s environment
1) Increased hazardous radiation
3) Magnetic storms
4) Atmospheric storms
How do astronomers check a theory of stellar evolution?
They predict what changes in luminosity and temperature should take place in stars as they age. Then they compare these theoretical tracks of evolution on H-R diagrams with H-R diagrams for groups of real stars.
The main source of energy for a main sequence star that shines into space
The nuclear fusion reactions in the core ( where hydrogen is converted into helium)
What determines the length of time it takes for stars of the same initial chemical composition to evolve?
When will the Sun leave the main sequence?
When all the available hydrogen fuel in its core is used up so that it no longer has an internal energy source
Is the space behind the “horse’s head” really empty of stars?
No. The “horse’s head” is a dark nebula. It is a relatively dense concentration of interstellar matter whose dust absorbs or scatters starlight and hides stars that are behind it from our view.
The main shapes of galaxies in the Hubble classification scheme
Elliptical, spiral, and irregular.
All contain old stars, so all must be equally old, therefore they cannot represent successive stages of galaxies’ evolution
The most popular explanation for the colossal energy output of active galaxies
A very massive object, probably a black hole, is at the galaxy’s center.
How do cosmological models differ from religious explanations of the universe?
Cosmological models do not give a supernatural cause or meaning to physical events, but try to explain these events using only the laws of nature and mathematics.
The two basic observations that can help decide the ultimate fate of the universe
1) The rate of change of the Hubble constant with time
2) Density of matter and energy in the universe
Cosmological significance of cosmic background radiation
The microwave radiation striking Earth from all directions in space and provides strong evidence for the Big Bang model. It appears to be the redshifted remnant of the radiation created in the Big Bang.
The main contribution of an inflationary universe model to the Big Bang theory
A brief phase of incredibly rapid expansion shortly after the Big Bang could explain how an explosive beginning could result in both the homogeneity of the cosmic background radiation and the large-scale structure of the observable universe.
The members of the solar system
One star, our sun, orbited by planets, moons, asteroids, comets, Kuiper Belt objects, and interplanetary gas and dust
The main difference between a planet and a dwarf planet
Mass. A planet has enough mass to clear the region around its orbit and a dwarf planet does not
What keeps the planets orbiting the Sun?
A combination of planet’s forward motion and their motion in toward the Sun under the Sun’s gravity
Famous visible features of the planets
Mars-Polar ice caps
Jupiter-Great Red Spots
Saturn- Rings (Five)
Why is Venus inhabitable and unable to be visited?
1) Poisonous carbon dioxide atmosphere
2) Much too hot (up to 900° F);
3) A crushing atmospheric pressure over 90 atmosphere.
Three observations that support the theory of plate tectonics (continental drift)
1) Similar plant and animal fossils are found along coastlines of South America and West Africa
2) These coastlines seem to fit together;
3) No rocks from the bottom of the Atlantic Ocean near the coastlines are older than about 150 millions years.
Why do some constellations only appear in the sky during certain seasons?
Because of the Earth’s revolution around the Sun (meaning the Sun will sometimes hide those stars because of its position relative to the Earth.)
Apparent vs. true brightness
Apparent brightness deals with how bright a star appears to be to the human eye, while true brightness doesn’t deal with the long distance and instead considers all stars’ luminosities at the same distance of 10 parses away and helps us to find the size of a star when we use parallax.
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with Earth. All objects in the observer’s sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.
Solar day vs. sidereal day
The solar day is about 4 minutes longer than a sidereal day because, while Earth rotates on it axis, it also moves along in its orbit around the Sun. Earth must complete slightly more than one whole turn in space before the Sun reappears on your meridian.
Use lens to reflect light (Problems of spherical aberration and chromatic aberration)
Use mirrors to reflect light (Newton’s idea)
Blackbody radiation curve
Somewhere in the range 900K to 1000K, the blackbody spectrum encroaches enough in the the visible to be seen as a dull red glow. Most of the radiated energy is in the infrared.
The Hertzsprung-Russell Diagram is a graphical tool that astronomers use to classify stars according to their luminosity, spectral type, color, temperature and evolutionary stage
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. Chemically, about three quarters of the Sun’s mass consists of hydrogen, while the rest is mostly helium. The remainder consists of heavier elements, including oxygen, carbon, neon and iron, among others. It is a G-type main sequence star and a supergiant.
A comet is an icy small Solar System body that, when passing close to the Sun, heats up and begins to outgas, displaying a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind upon the nucleus of the comet. They are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus
The Oort cloud (named after the Dutch astronomer Jan Oort) is a hypothesized spherical cloud of predominantly icy planetesimals that may lie roughly 50,000 AU, or nearly a light-year, from the Sun.
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks (“occults”) the Sun. This can happen only at new moon, when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy.Since looking directly at the Sun can lead to permanent eye damage or blindness, special eye protection or indirect viewing techniques are used when viewing a solar eclipse. A total solar eclipse lasts for only a few minutes at any given place, due to the smaller size of the moon’s shadow.
A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra (shadow). This can occur only when the Sun, Earth, and Moon are aligned (in “syzygy”) exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a full moon. They lasts for a few hours and are safe to view without any eye protection or special precautions, as they are no brighter (indeed dimmer) than the full moon itself.
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The “electromagnetic spectrum” of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.
Oscillating electrons emit radiation and create light
Fixed wavelengths emitted. Based on Bohr model, wherein electrons switch to lower orbitals in atoms
Certain wavelengths left out (Image of rainbow with black ‘absorption’ lines). Certain chemicals/elements cause the selection/exclusion of particular wavelengths (Some elements absorb a few waves of light, leaving the others to be emitted)
Stuff we cannot see that causes gravity. Makes up 23% of the universe. Doesn’t emit electromagnetic radiation or absorb it.
Migration of planets
Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite’s orbital parameters, especially its semi-major axis. Planetary migration is the most likely explanation for hot Jupiters, extrasolar planets with jovian masses, but orbits of only a few days.
Regions of a star
Atmosphere, photosphere, limb, chromosphere, corona, interior, radiation zone, and convection zone