AS101

What is the astronomical unit used for?

Used to measure distances greater than the distance between the Earth and the moon

What is the length of one astronomical unit?

The distance between the Earth and the Sun

Is the astronomical unit changing?

Since the universe is expanding, the astronomical unit is changing in distance very slowly

How many stars does the Milky Way contain?

100x10^9 stars

What is the Milky Way's diameter?

80 000 light years

Is the Milky Way a typical spiral galaxy?

Yes but it is larger than most

What is a supercluster?

A cluster of galaxy clusters

Why do superclusters form?

Galaxies are not uniformly distributed in the universe and most are drawn together in groups and clusters with groups containing up to some dozens of galaxies and clusters hold several thousand galaxies

What are filaments?

The largest structures in the universe

What are cosmic voids?

The vast empty spaces between filaments

What is the diameter of a cosmic void?

Typically, cosmic voids have a diameter of 11 to 150 megaparsecs

What are super voids?

Large voids defined by the absence of rich super clusters

What is the difference between cosmic voids located in high-density environments than ones located in low-density environments?

Cosmic voids located in high-density environments are smaller than cosmic voids in low-density environments

What are constellations?

Regions of the sky containing a star pattern

Which language is used to denote a star's brightness?

Greek

What does α mean?

The brightest star

What does β mean?

The second brightest star

How is the brightness of stars measured?

Astronomers use the magnitude scale which states that the larger the magnitude, the fainter the star

What is the apparent visual magnitude?

The brightness of a star as seen by human eyes on Earth

What is flux?

The measure of the flow of energy out of a surface such as a star

What is the celestial sphere?

An imaginary sphere surrounding the Earth with celestial objects attached

What is the cause of the westward motion of the sky?

The eastern rotation of the Earth

What does the appearance of the sky depend on?

The observer's location on Earth

What are astronomical distances measured in on the celestial sphere?

Degrees

What is zenith?

The point directly above the observer

What is nadir?

The point on the celestial sphere directly below the observer, opposite of the zenith

What is rotation?

The motion around an axis passing through a rotating body

What is revolution?

The orbital motion about a point located outside the orbiting body

What is precession?

The slow change in orientation of the Earth's axis of rotation over thousands of years (260 000 years to be exact)

What are seasons caused by?

The changes in the amount of solar energy that Earth's northern and southern hemispheres receive at different times of the year

What is the ecliptic?

The sun's apparent path around the sky

Which direction does the Sun appear to move on the celestial sphere?

West to east

Which direction does the Sun appear to move in the sky?

East to west

What is the celestial equator?

The imaginary line around the sky directly above Earth's equator

What are the North and South celestial poles?

Points on the celestial sphere directly above Earth's North and South poles

When does the summer solstice occur?

Twice yearly, when one of Earth's poles has its maximum tilt towards the sun

What is Earth's maximum axial tilt toward the sun during the summer solstice?

23.44°

What is the Sun's declination from the celestial equator during the summer solstice?

23.44°

Does the side of the moon facing the Earth change?

No, the moon always keeps the same side facing Earth

What is the orbital period of the moon around the Earth?

27 days

What is the length of a moon phase?

29.5 days

Does everyone see the same moon phase on the same day?

Yes

How do the Northern and Southern hemispheres' views of the moon differ?

They see the moon oriented differently with respect to the horizon and they see the moon apparently upside-down with respect to each other

How many moon phases are there?

8

What would change if the Moon was in a perfectly circular orbit, a little closer to the Earth, and in the same orbital plane?

There would be total solar eclipses every new moon

Why does the Moon's shadow usually miss Earth?

Because the Moon's orbit is tilted at more than 5° to the Earth's orbit around the Sun

When can a solar eclipse occur?

Only when the Moon is close enough to the ecliptic plane during a new moon

What is the umbra?

The region of a shadow that is totally shaded

What is the penumbra?

The portion of a shadow that is only partially shaded

What happens to the Moon during a lunar eclipse?

It becomes darkened as it moves through Earth's shadow

Why does the Moon darken and turn copper-red?

Because of sunlight refracted through Earth's atmosphere

What coordinate system does the celestial sphere use?

A coordinate grid similar to the longitude and latitude system used on Earth

What are stellar coordinates?

The angular distances of an object on the celestial sphere and they describe locations of celestial objects in the sky

What is declination?

The angular north-south distance measured from the celestial equator and is measured in degrees

What is right ascension?

The angular east-west distance measured from the vernal equinox

What is a solar day?

The average time between successive crossings of the Sun on the local meridian

What is a sidereal day?

The time between successive crossings of any star on the local meridian

What is a sidereal month?

The time for the moon to orbit Earth once relative to any star

What is a sidereal year?

The time for the Earth to complete one full orbit around the Sun relative to any star

What is a synodic month?

The time for a completion of lunar phases and is about 19.5 days

What is a tropical or solar year?

The time between successive spring equinoxes

How did ancient people of central Africa predict seasons?

They observed the Moon

What is the Stonehenge located in England?

An ancient site that may have served as an observatory, completed in 1550 BCE

What were Babylonians known for in astronomy?

They were some of the most meticulous record keepers as recorded detailed observations of the visible planets and recorded a solar eclipse

What did China record in astronomy?

China is responsible for the earliest known record of a supernova explosion in 1440 BCE and the record of another supernova explosion in 1054 CE

Where was the home of Minoan astronomers?

The island of Crete

What did Minoan astronomers know of?

They knew about fractions, number sequences, math operations, and were knowledgeable of the constellations and their movements in the sky

How did Minoan astronomers heat water in the king's palace?

They used mirrors

Did Minoan astronomers use solar and planetary calendars?

Yes

How many planets did Minoan astronomers know of?

5

How did Minoan astronomers predict when their women would give birth?

They used the orbit of Venus

Did Minoan astronomers know of the equinoxes?

Yes

What calculator is also used to depict the periodic motion of Jupiter?

A Minoan calculator

How many days are needed for Venus to come up to a conjunction?

584 days

With the Minoan calculator, what is 265 equal to?

9 months, which is the time before the birth of a baby

What were the Greeks responsible for from 900 BCE to 0 CE?

They were among the first to develop models and scientific methods to explain their observations of the universe

What did Thales of Miletus do?

He correctly predicted a solar eclipse

What did Pythagoras suggest?

That the Earth is a sphere and not flat

What did Eratosthenes calculate?

The Earth's circumference

Who contributed to the knowledge of astronomy from 0 CE to 1500 CE?

Astronomers from Greece, the middle east, and India

Who was Hypatia?

A female astronomer and mathematician and was the director of the observatory in Alexandria

Who was Aryabhata?

An Indian astronomer and mathematician known for Aryabhatiya

What did Aristotle believe motion in the perfect heavens was caused by?

The rotation of spheres carrying objects around in uniform circular motion

When did Claudius Ptolemy give mathematical form to Aristotle's model?

140 CE

What did Claudius Ptolemy add to the geocentric principle?

Off centre circles and variable speeds to better predict the motion of the planets

What did ancient Greek philosophers and astronomers believe?

That heavenly objects moved on circular paths at a constant speed, with Earth motionless at the centre of the universe

What did Ptolemy create?

An elaborate geometrical and mathematical model to explain details of the observed motions of the planets, while assuming Earth is motionless at the centre of the universe

What did Nicolaus Copernicus propose?

A heliocentric model of the universe, he was the first to do so

Who was Tycho Brahe?

A Danish nobleman and astronomer that built an observatory and spent 20 years measuring the positions of the stars and planets

What did Johannes Kepler discover?

The three laws of planetary motion, which include:

o The orbits of the planets are ellipses with the Sun at one focus

o A line from a planet to the Sun sweeps over equal areas in equal amounts of time

o A planets orbital period squared is proportional to its average distance from the sun cubed

What happened to Galileo Galilei in 1616?

Cardinal Bellarmine ordered him to cease public debate about models of the universe

What happened to Galileo Galilei in 1633?

Galileo was condemned for refusing to obey an order to halt his defense of Copernicus' model

When did Isaac Newton make most of his discoveries?

During 1665 and 1666

Which laws did Isaac Newton discover?

Using the work of Kepler and Galileo, Newton discovered three laws of motion and the law of gravity

What is speed?

The rate at which an object moves

speed = distance/time

What is acceleration?

The rate of change of velocity with time

acceleration = velocity/time

What does the gravitational force of attraction between two objects depend on?

The product of the masses of the two objects

What is inverse square relation?

A rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases

What are tides caused by?

Small differences in gravitational force

What is spring tide?

An ocean tide of large range that occurs at full and new moon