Galaxy Types/Big Bang/Sun and Moon

Question 1

The vast majority of observed ____________ fall into two general classes: spirals and elliptical.

Answer 1

Galaxies. In addition, a small minority of galaxies are classed as irregular.

Question 2

Our own galaxy (the Milky Way) and M31 (the Andromeda Galaxy) are both typical ______________ galaxies.

Answer 2

Spiral. A spiral consists of a nucleus, a disk, a corona, and spiral arms. Interstellar material is usually observed in the arms of spiral galaxies and bright emission nebulae are present. Other famous spiral galaxies include M81 - Bodes Galaxy (left image below) and M33 - Traingulum Galaxy (right image):

Question 3

While more than two-thirds of the most conspicuous galaxies in the sky are spirals, there are many dwarf galaxies which fall into the class of ______________ galaxies.

Answer 3

Elliptical. Elliptical galaxies are spherical or ellipsoidal systems which consist entirely of stars with no trace of spiral arms.

Question 4

The distribution of ________________ in a typical elliptical galaxy shows that while it has many stars concentrated toward its center, a sparse scattering of stars extends for very great distances and merges imperceptibly into the void of intergalactic space.

Answer 4

Light. This scattering of outlying stars makes determining the total size of an elliptical galaxy difficult. The fact that elliptical galaxies are not disk-shaped shows that they are not rotating as rapidly as the spirals.

Question 5

Elliptical galaxies have a much greater range in size, mass, and _______________ than do the spirals.

Answer 5

Luminosity. The rare giant ellipticals, such as M87, are more luminous than any known spiral. Below is a photo of M87; the light in the upper left is of the stars that make up the galaxy, while what you see extending away from that light towards the lower right is a jet of matter ejected from the galaxy, possibly due to a black hole:

Question 6

Elliptical galaxies range in size from the giants (such as M87 mentioned in the last question) to __________, which are believed to be the most common kind of galaxy.

Answer 6

Dwarfs. There are so few bright stars in this type of galaxy that even its central regions are transparent. The total number of stars, however, may be as many as several million. Below is a pic of M110, a dwarf elliptical galaxy and the last object to be added to the Messier catalog:

Question 7

About three percent of the brightest appearing galaxies in the northern sky are classified as _____________.

Answer 7

Irregular. They show no trace of circular or rotational symmetry. Their appearance is irregular and chaotic:

Question 8

The continuity of the morphological forms of galaxies along classification sequences suggests that these different forms might represent stages of _______________ for galaxies.

Answer 8

Evolution. Elliptical galaxies may always have been elliptical, but they may have had supergiant stars when they were young. Spirals may never become elliptical, but eventually their spiral arms may disappear when virtually all of their interstellar matter is converted into stars. However, the evolution of galaxies is still speculative due to the youth of Astronomy.

Question 9

______________ of galaxies can be roughly classified into two categories: regular clusters and irregular clusters.

Answer 9

Clusters. Almost all galaxies may be members of groups of clusters. Clusters of galaxies are now regarded as fundamental condensations of matter in the universe.

Question 10

The ______________ clusters have spherical symmetry and show marked central concentration.

Answer 10

Regular. They tend to be very rich clusters and most of them probably contain at least a thousand members. The regular clusters have structures resembling those of globular star clusters. Regular clusters consist almost entirely of elliptical galaxies.

Question 11

The _____________ clusters, sometimes called open clusters, have a more formless appearance and possess little or no spherical symmetry or central concentration.

Answer 11

Irregular. The irregular clusters sometimes have several small sub-condensations and resemble loose swarms of small clusters. They contain all kinds of galaxies — spirals, elliptical, and irregulars. Irregular clusters are more numerous than the regular clusters and range from rather rich aggregates of more than a thousand galaxies to small groups of a few dozen members or less.

Question 12

The cluster of galaxies to which our galaxy belongs is called the __________ group.

Answer 12

Local. The Local Group comprises over thirty-five galaxies. The two most massive galaxies of the Local Group are the Milky Way and the Andromeda Galaxy.

Question 13

Beyond the Local Group, at distances of a few times its diameter, we find other similar small groups of ____________.

Answer 13

Galaxies. The nearest rich cluster of neighboring galaxies is the Virgo cluster, so named because it is in the direction of the constellation Virgo. Comprising approximately 1,300 member galaxies, the cluster forms the heart of the larger local Local Supercluster, of which the Local Group is an outlying member.

Question 14

Considerable matter exists in _______________ space that is not associated with a galaxy or cluster.

Answer 14

Intergalactic. It is assumed that such matter exists outside any specific area for three reasons: If galaxies have formed from gas and dust, some of this pre-galaxian material could well have been left over; individual, rapidly moving stars occasionally escape from galaxies and from star clusters; and collisions or tidal interactions between galaxies could sweep interstellar matter from them.

Question 15

A theory about the origin and development of the universe is called a _______________.

Answer 15

Cosmogony. This study refers to theories of the creation of the universe (cosmos). It differs from cosmology in that cosmology is the science of the universe; cosmology includes cosmogony, but it seeks to do much more–explain the composition of the universe and the laws governing it, while cosmogony seeks to simply explain how the universe came to be.

Question 16

The term ______________ embraces not only cosmogony, but also the content and organization of the universe.

Answer 16

Cosmology. Cosmology is a study of the universe as a whole–what happened in its past and what will happen in the future.

Question 17

The ____________ velocity of galaxies is the component of relative velocity that lies in the line of sight.

Answer 17

Radial. Remember that velocity consists not only of speed, but also of direction. The radial velocity of a galaxy is its velocity in the line of sight, or in other words its speed straight towards you or away from you. Evidence from the radial velocities of the galaxies acknowledges that the universe is expanding. The first radial velocities of galaxies were measured by V. M. Slipher at the Lowell Observatory.

Question 18

The more distant a galaxy, the greater, in direct proportion, its speed of _______________, as determined by the shift of its spectral lines to the longer (or red) wavelengths.

Answer 18

Recession. By the 1930’s, M.L. Humason and Edwin Hubble had begun to photograph spectra of fainter galaxies and found that in general, the fainter and smaller a galaxy appeared, the higher was its redshift. This was then interpreted to mean that the more distant a galaxy, the higher its speed of recession–in other words, the faster it’s moving away from us. This finding is known as the law of red shifts; it is often simply referred to as Hubble’s Law.

Question 19

The currently most widely accepted theory for how the universe was formed is the ______ ________ theory.

Answer 19

Big Bang. According to the Big Bang theory, the universe started around 12 to 14 billion years ago. There are other theories which have been espoused by big name scientists, but currently the Big Bang theory is the most commonly accepted and well-known explanation for how the universe came to be.

Question 20

In the Big Bang theory, everything originated from a single tiny, infinitely dense and hot and massive point known as a ______________.

Answer 20

Singularity. Inside of this singularity was contained all of the matter and energy of the universe, which means nothing (not even space) existed outside of it. This singularity then expanded into the universe as we know it today.
Note that at the core of each black hole is also thought to exist a singularity. A singularity simply refers to a point of infinite density and infinitesimal (immeasurably small) volume. It is imagined that in a singularity, space and time would become infinitely distorted.

Question 21

There are three main ideas which are seen as supporting evidence by proponents of the Big Bang theory. The first is that according to Hubble’s Law, the universe is ______________.

Answer 21

Expanding. As you recall, Hubble discovered that the light coming from almost all galaxies is redshifted (only about 100 galaxies have been recorded which are blueshifted), which he interpreted to mean that they are moving farther away and that the universe is expanding. This would suggest that at one time the universe was compacted.

Question 22

The second big idea seen to support the Big Bang theory was the discovery of ________ radiation.

Answer 22

Cosmic Microwave Background (CMB) radiation. In 1948, three scientists Gamow, Alpher, and Herman predicted that based on the idea that the universe started out hot and dense, and proceeded to expand and cool, that there should be some kind of relic radiation left over spread out throughout the universe.
In 1965, two radioastronomers, Penzias and Wilson, discovered what is cited today as one of the most compelling pieces of evidence of the Big Bang–microwave radiation with a temperature of about 2.7K that uniformly pervades the entire observable universe. This radiation, known as CMB radiation, is interpreted to be the left over heat from the Big Bang.

Question 23

The third idea used to support the Big Bang theory is the idea of Big Bang _______________, which suggests that the universe should mainly consist of light elements such as helium.

Answer 23

Nucleosynthesis. The idea of Big Bang Nucleosynthesis is that within the first few minutes of the Big Bang, temperatures and densities were high enough that protons and neutrons floated as free particles–not bound up in atoms. For the first fifteen minutes or so, these particles underwent nuclear fusion, forming light elements such as helium and hydrogen (a specific type of hydrogen called deuterium).
The idea is that there were only a few minutes for these reactions to occur because the universe was expanding rapidly–temperature and density were dropping. So, there was no opportunity for heavier elements to form. Therefore, the universe should consist almost entirely of light elements. Investigation shows that indeed, the older an object is in space, the less heavy elements it contains, but even really old objects contain at least 25% helium.
The gist is, the abundance of light elements such as Helium (almost 25% of matter in the universe) and Hydrogen (about 3/4 of all matter) is seen as one of the big three pieces of evidence to support the Big Bang theory.

Question 24

The gravitational attraction of the moon and sun, acting on the Earth, has two consequences that arise because the Earth is not a perfect __________ but rather an ablate spheroid.

Answer 24

Sphere. Since the Earth is not exactly spherical, its curvature varies with location.

Question 25

The shape of the Earth and the _______________ pull of the moon and the sun cause two phenomena: the tides and precession.

Answer 25

Gravitational.

Question 26

The differential gravitational forces of the moon’s attraction on different parts of the Earth with respect to its center are called __________ forces.

Answer 26

Tidal. The areas of the Earth facing the moon have a higher gravitational pull than those away from the moon. This pull causes the Earth to slightly distort, rising up and down and tilting as a fluid surface, causing the sea level changes. The pics below show the same bay at high tide and at low tide:

Question 27

The _______ also produces tides on the Earth, although it is less than half as effective a tide-raising agent as the moon.

Answer 27

Sun. Actually, the gravitational attraction between the sun and the Earth is about 150 times as great as that between the Earth and the moon. However, the sun is so distant that it attracts all parts of the Earth with almost equal strength. The moon is close enough for its attraction on the near side of the Earth to be substantially greater.

Question 28

When the sun and moon are lined up (at a full moon), the tides produced are greater than normal and these are called _________ tides.

Answer 28

Spring. The spring tides are the highest tides that the Earth experiences. Of these high tides, the highest occur at those times during a full moon when the moon is closest to the center of the Earth.

Question 29

When the moon is at its first or last quarter, the tides produced by the sun partially cancel out the tides of the moon and these are called _________ tides.

Answer 29

Neap. The neap tides are lower than usual on the Earth.

Question 30

The Earth is not perfectly spherical and its equatorial diameter is twenty-seven miles greater than its _________ diameter.

Answer 30

Polar. A perfect sphere would have the same diameter at all points.

Question 31

_______________ is a slow, conical motion of the Earth’s axis of rotation caused by the gravitational torque of the moon and the sun on the Earth’s equatorial bulge.

Answer 31

Precession. The Earth’s rotation axis is not fixed in space; it is moving like the top of a wobbly top as illustrated by the animation below. Of course by human standards, this conical motion is imperceptible–with a precession period of 26,000 years, it takes 26,000 years for the Earth’s axis to do a full rotation.
Another way to look at this is that right now the North Star is Polaris, but in 13,000 years the star Vega will be approximately at the North Celestial Pole. Then in 26,000 years, the pole will be pointing in the same direction again–back at Polaris.

Question 32

The twenty brightest stars as seen from Earth are classified in that manner because they have high ______________ and/or are nearby.

Answer 32

Luminosity. Those stars are: Sun, Sirius, Canopus, Arcturus, Alpha Centauri, Vega, Rigel, Procyon, Achernar, Betelgeuse, Hadar (Agena), Capella A, Altair, Aldebaran, Capella B, Spica, Antares, Pollux, Fomalhaut, and Deneb.

Note that many people mistakenly think that Polaris, the North Star, is the brightest star in the sky, when it’s actually #48 on the list. Sirius is the brightest star after the sun.

Question 33

A visual grouping of five galaxies of which four form the first compact galaxy group ever discovered is called the ______________ ______________.

Answer 33

Stephan’s Quintet. This group was discovered by Edouard Stephan in 1877 and is one of the most studied of all the compact galaxy groups.

Question 34

The length 206,265 AU (astronomical units) is defined as a _____________.

Answer 34

Parsec. A parsec is 206,265 AU, which is about 30 trillion kilometers (19 trillion miles) or 3.262 light years. The name parsec stands for “parallax of one second of arc” and the concept is based on trigonometry.
A parsec is too big of a unit to use within our solar system, which is only around 1/2600th of a parsec across. Typically you would describe the distance between nearby stars in parsecs, kiloparsecs for the distance between parts of a galaxy or within galaxy groups, and megaparsecs for distances between galaxy clusters.

Question 35

_____________ is the change of angular position of two observations of a single object relative to each other as seen by an observer, caused by the motion of the observer.

Answer 35

Parallax. This is the apparent shift of an object against the background that is caused when the observer changes positions. When standing in one place it looks one way; if the observer moves, the background changes and the object looks different. The below graphic shows a simple demonstration of how the same star would look different when the Earth is in two different parts of its orbit around the sun:

Question 36

____________ are highly magnetized rotating neutron stars which emit a beam of detectable electromagnetic radiation in the form of radio waves.

Answer 36

Pulsars. The radiation can only be observed when the beam of emission is pointing towards the Earth. Most pulsars actually are detectable only by their radio radiation–they release too little visible light to be seen with the human eye.
Because neutron stars are very dense objects, the rotation period and the interval between observed pulses are very regular.

Question 37

A ____________ is an extremely bright and distant active galactic nucleus–the very bright center of a distant galaxy powered by a black hole in the galaxy in which it’s located.

Answer 37

Quasar. Quasars were first identified as high redshift sources of electromagnetic energy including radio waves and visible light. They are considered the most distant objects discovered by astronomers, so far away that their light takes billions of years to reach the Earth. For this reason, the study of quasars gives astronomers a glimpse into the early stages of the universe.
They radiate enormous amounts of energy and are the most luminous objects ever detected, some being as much as a trillion times brighter than our sun. The currently accepted definition is that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy.

Question 38

____________ occurs when the frequency of a photon of light is shifted towards the red end of the electromagnetic spectrum.

Answer 38

Redshift. A shift towards the red end of the spectrum indicates lower energy, which means longer wavelength. As you have learned earlier, one instance in which redshift is observed is when a light-emitting object (such as a distant galaxy) is moving further away. As it moves away, the wavelength of the light is stretched out, causing the light to shift towards red. On the other hand, if the source of the light were moving closer, blueshift would result as the wavelength of the light gets compressed (higher energy, higher frequency, lower wavelength)

Question 39

_______________ redshift is caused by the expansion of the universe

Answer 39

Cosmological. As the light is moving from its point of emission (i.e. a distant galaxy) to the point of detection (i.e. Earth), the fact that the universe is expanding and the space between the point of emission and detection is increasing results in an increase in the wavelength of the light (lower energy, a shift towards red).

Just picture the light, which is taking millions of years to arrive at your telescope, is being stretched as the universe it is passing through is stretching. This will obviously result in a longer wavelength.

Question 40

A ________________ black hole has a mass of up to tens of billions of solar masses.

Answer 40

Supermassive. It is believed that all galaxies contain supermassive black holes at their galactic centers. Two supermassive black holes can co-exist in the same galaxy for a certain amount of time.

Question 41

The ___________ mass is a standard way to express mass in astronomy and is used to describe the masses of other stars and galaxies.

Answer 41

Solar. Solar mass is equal to the mass of the sun, about 332,950 times the mass of the Earth. The accepted symbol and value for solar mass is:

Question 42

A __________ ________ is the distance light travels in a vacuum in one year.

Answer 42

Light year (LY): A light year is equal to exactly 9,460,730,472,580.8 km (9 trillion kilometers), about 5,878,625,373,183.61 statute miles (6 trillion miles), or about 0.3066 parsecs.

Question 43

Venus, Earth, and Mars possess conditions under which there can be remote speculation of living organisms and of these three, only __________ offers conditions compatible with the existence of higher forms of plant or animal life as we know them.

Answer 43

Earth. The possibility of life processes unknown to us cannot be ruled out. With the possible exception of vegetation on Mars, we have no knowledge of any life on other planets of the solar system.

Question 44

Life may abound in the universe or it may be unique to the __________.

Answer 44

Earth. It is not known exactly how life began on our own planet. Therefore, we have no objective means of assessing the probability of life beginning elsewhere or the likelihood of the critical steps of evolution which may lead to intelligent beings.