Unit 1 (Chapters 1-4)

Question 1

What direction does the decimal move in scientific notation if exponent is + or -?

Answer 1

x10^- = move decimal to the left
x10^+ = move decimal to the right

e.g. 43x10^-6 = 0.000043
e.g. 573x10^+9 = 573,000,000,000

Question 2

Define the following terms:
- Solar system
- planets
- stars
- Dwarf planet
- Extra solar planets
- Galaxy

Answer 2

• Solar System: the sun, its family of planets, and some smaller bodies such as moons, asteroids etc.
• Planets: spherical non-luminous bodies that orbit a star ad reflect light
• Stars: Self luminous balls of hot gas
• Dwarf Planets: a body which meets some but not all the qualities of a plant
• Extra solar planets: families of planets that orbit stars besides the sun
• Galaxy: a great cloud of stars, gas, and dust held together by the combined gravity of all its matter

Question 3

How big is an Astronomical unit? How big is a light year?

Answer 3

An AU is equal to 150 million km.
A ly is equal to 63 000 AU

Question 4

What are the order of the plants from the sun

Answer 4

Sun, mercuiry, venus, earth, mars, jupiter, saturn, uranus, neptune

Question 5

What are the basic characteristics of a galaxy? What about our galaxy?

Answer 5

A galaxy is made up of stars, gas, and dust held together by the combined gravity of all its matter.

It can range in size from 1000ly to 300 000 ly

Can contain 1 trillion+ stars

There are billions of galaxies in the universe

The Milky Way galazy is ~80 000 ly

Question 6

What is the relative timeline of our universe?

Answer 6

Big Bang: ~14 billion years ago
First stars: ~ 13.5 billion years ago
Our solar system: ~ 4.6 billion years ago
First life on earth: ~ 3.4 Billion years ago
First life on land: ~400 million years ago
Dinosaur extinction: ~65 million years
First human like creature: ~4 million

Question 7

What is a constellation?

Answer 7

It is a group of stars

The constellations named within western culture originated in the civilizations of Assyria, Babylon, Egypt, and Greece ~3000 years ago

Question 8

How many constellations are there and how does this relate to asterisms?

Answer 8

The International astronomical union has established 88 official constellations with carefully defined boundaries that make up the night sky.

Asterisms are less formally defined groupings of stars which are not considered official constellations (e.g. the big dipper)

Question 9

How are stars organized within a constellation?

Answer 9

Stars within a constellation are organized via the Bayer’s designation where the Greek Alphabet and the genitive form of the constellation’s name are used. The brightest star in the constellation is the alpha and then they are ordered by brightness

Question 10

How is star brightness measured?

Answer 10

Star brightness is measured using the magnitude scale which has 6 classes from magnitude 1 (brightest) to 6 (least bright)

Magnitude only measures visible light and is measured in Apparent visual magnitude or Mv

Question 11

What is Flux and Flux ratio? What are their uses?

Answer 11

Flux is the light energy from a star that hits a collecting area of 1 square meter in 1 second

A flux ratio will tell you how many times brighter a star is based on their magnitude . It can also be used to find the difference in magnitude between 2 stars.

Question 12

Which direction does the earth rotate and which direction does it APPEAR to rotate?

Answer 12

Rotates eastward but appears to rotate westward.

Question 13

What are zenith and nadir?

Answer 13

Zenith: above your head
Nadir: below your feet

Question 14

What is the celestial equator?

Answer 14

the points between the apparent pivot points (north celestial pole and south celestial pole)

The north point and south point are the points on the horzian that are closest to the celestial poles, the west and east points are halfway between the north and south

Question 15

How is the distance between celestial objects measured?

Answer 15

Angluar distance is used to measure the distance between two objects.

Angular distance is measured in arc minutes (1/60 of a degree) or arc seconds (1/60 of an arc minute)

Angular distance can also be used to measure angular diameter, the distance of an object from one edge to another

Question 16

What is precession? How does this relate to earth’s orbit?

Answer 16

Precession is when the weight of the top of a rotating object makes its axis sweep out like the shape of a cone.

For example: the earth moves in a cone shaped orbit because a combination of the twisting axis and rotation of the earth. The axis twists Because earth’s axis is tipped at 23.4 degrees from vertical and the earth’s bulge around the middle is pulled by the gravity of the sun and moon which twists the earths axis upright relative to it’s origin.

Earth’s precession takes about 26 000 years

Question 17

What causes day/night and seasons?

Answer 17

Earths rotation (turning on it’s axis) causes day and night.

Earths revolution (motion around a point outside the body) around the sun causes seasons
- Seasons are caused by the sun’s movement from the southern to the northern half of the sky.

Question 18

What is the ecliptic? How are they related to the equinoxes and solstices?

Answer 18

Ecliptic is the path of the sun against the background of the stars.

The sun appears to move eastward across the sky and travels about 1 degree every 24 hours

Equinox is when the celestial equator and ecliptic cross at either the southern point (Autumnal Equinox) or the northern point (Vernal Equinox)

Solstices are when the sun is at either the most Northern point of the ecliptic (Summer solstice) or the most southern point of the ecliptic (winter solstice)

Question 19

What are morning and evening stars?

Answer 19

Morning stars are planets visible at sunrise and evening stars are planets visible at sunset.

Question 20

What is the Milankovitch Hypothesis?

Answer 20

This hypothesis suggests that small changes in the shape of Earth’s orbit and axis inclination along with a subtle effect of precession could combine to influence the earth’s climate a cause ice ages.

Ocean temperature measures historically show strong evidence for this theory but also suggest that there is more involved that we don’t yet know.

Question 21

What is a local group?

Answer 21

It is our group of galaxies near by. The milky way and Andromeda galaxy are the 2 largest members of the local group.

The local group is part of a larger ensemble of galaxies in the Virgo Cluster

Question 22

Describe the moon’s orbit around Earth.

Answer 22

The moon revolves counter clockwise, moving 13degrees in 24 hours.

It’s orbit is tipped at 5degress so it is always near the ecliptic.

The same side of the moon is always facing the earth.

Question 23

Describe the Lunar Phase Cycle and key phases to remember.

Answer 23

The lunar phase cycle is the changing appearance of the moon as it revolves around the earth. Only portions of the sunlit area are visible from earth.

Key Phases:
- New moon: the moon is between the sun and the earth so the sun illuminates the far side of the moon (this is when the moon is least visible)
- Full moon: the earth is between the moon and the sun so the side visible from earth is fully lit (this is when the moon is most visible.
- Waxing moon: this is when the is moving from new moon to full. it takes 14 days and includes the phases new moon, waxing crescent, first quarter, waxing gibbous, and full.
- Waning moon is when the moon is going from full to new.
It takes 14 days and includes the phases full, waning gibbous, third quarter, waning crescent, and new moon.

Question 24

What is the difference between the sidereal period and the synidic period

Answer 24

Sidereal period: how long it takes the moon to circle the sky once and return to it’s original position relative to the stars (27.3 days)

Synidic Period: how long it takes for a complete cycle of lunar phases (29.5 days)

Question 25

What are the 2 parts of a shadow and how do they cause a lunar eclipse?

Answer 25

A shadow has two parts 1. Umbra: the region of total shadow 2. Preumbra: the edge of light creating a partial shadow. The umbra of earth's shadow is 3x longer than the distance of the moon and 2.5x the diameter of the moon. When the moons orbit carries it through the earth's umbra, it causes a total lunar eclipse. As the moon moves into the preumbra, it dims, and then it enters the umbral shadow and goes dark, before re-entering the preumbra and then returning to full brightness. Lunar eclipses only occur on full moons and happen 1-2 times a year. They tend to last about 6 hours with 1 hour and 45 minutes being in the actual umbra

Question 26

What affects the darkness of a total lunar eclipse?

Answer 26

Three factors - location in the umbra, the more central the darker it is - earth atmosphere, the more cloudy, the darker it is - earth;s atmosphere dust, the more dust, the darker it is.

Question 27

What is the difference between a partial and preumbral lunar eclipse?

Answer 27

Partial: the moon only partially passes through the umbra. Preumbral: the moon only passes through the preumbra.

Question 28

What is a solar eclipse? What are the different kinds?

Answer 28

When the moon moves between the earth and the sun. Only occurs during a new moon. Can last up to 7.5 minutes but usually only lasts 2-3. - A total solar eclipse is when the moon covers the disk of the sun completely - a partial solar eclipse is when the moon only covers part of the disk of the sun. Whether you see a total or partial solar eclipse depends on your location on earth. If you are in the path of totality (the track of the moon's shadow during an eclipse) you will see a total solar eclipse, if you are outside this path you will only see a partial eclipse. - there is also the annular eclipse where the moons umbral shadow (due to multiple factors) is not large enough to reach earth therefore a ring of light is visible around the sun.

Question 29

What is the diamond ring effect?

Answer 29

During a total solar eclipse, the ring of the corona and a bright spot of the photosphere are visible and resemble a large diamond ring.

Question 30

What are the conditions for an eclipse?

Answer 30

Each month the moon crosses the ecliptic twice (at nodes) Eclipses only happen when the sun is near one of these nodes When the sun and moon are at the same node and the moon is new, we get a solar eclipse When the sun and moon are at opposite nodes and the moon is full, we get a lunar eclipse.

Question 31

What is Archaeoastronomy?

Answer 31

the study of astronomy of ancient peoples.

Question 32

Where did Greek astronomy start and what role did they play in the formation of astronomy? What key beliefs did they have which affected their astronomy?

Answer 32

The Greeks derived astronomy from the Babylon and Egypt. They removed religion and astrology from the study and added logic and reason (but no scientific method) They believed - in a geocentric universe where the earth was the centre of the universe - they believed that the universe and the human mind were both rational therefore the human mind could understand the universe

Question 33

What role did Pythagoras, Philolaus, Plato, Aristotle, Hipparchus, and Ptolmy play in astronomy?

Answer 33

- Pythagoras: suggested things in nature were governed by geometric and mathematical relations - Philolaus: first to suggest the earth is in motion - Plato: suggested the uniform circular motion idea; the idea that the perfect heavens could move only by constant motion along a circular orbit - Aristotle: operated on first principles, the idea that something could be obviously true and not need explanation and therefore could be the starting point for rational thought. Led to lots of problems in thoery becasue some "first principles" were that the earth is the centre of the universe, the heavens are perfect etc. - Hipparchus: created the first star catalogue and discovered precession - Ptolmy: transferred Aristotle's universe into a sophisticated mathematical model.

Question 34

What was the copernican Revolution?

Answer 34

Was proposed that the universe was heliocentric with a rotating earth. This explained the motion of the planets. This model still used Plato's ideas of uniform circular motion but the hypothesis was otherwise correct.

Question 35

What was Tycho's contribution to astronomy?

Answer 35

developed a highly accurate way to measure star and planetary positions

Question 36

What are Kelper's three laws of planetary motion?

Answer 36

1. The orbits of the planets are ellipses with the sun at one focus 2. the line from a planet to the sun sweeps over equal areas in equal intervals of time 3. A planet's orbital period squared is proportional to it's average distance from the sun. A very accurate way to describe planetary motion and are still used today.

Question 37

What were Galileo's key discoveries?

Answer 37

- the moon has imperfections - there exist stars that can only be seen with telescopes - the FOUR Gililean moons of jupiter - Sunspots - Venus goes through a complete set of phases which means it must rotate around the sun.