Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Astro 18 > Module 4 > Flashcards

Module 4 Flashcards

1
Q

What is the primary focus of the chapter on Celestial Timekeeping and Navigation?

A

To explore the apparent motions of the Sun, Moon, and planets to understand timekeeping and navigation by the stars.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What defines a sidereal day?

A

The time it takes for any star to go from its highest point in the sky one day to its highest point the next day, approximately 23 hours 56 minutes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does a solar day differ from a sidereal day?

A

A solar day is based on the time it takes for the Sun to make one circuit around the local sky, averaging 24 hours, which is about 4 minutes longer than a sidereal day.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a synodic month?

A

The time it takes for the Moon to complete a cycle of phases from one new moon to the next, influenced by Earth’s motion around the Sun.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the duration of a sidereal month?

A

About 27.3 days, which is the true orbital period of the Moon relative to distant stars.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What defines a tropical year?

A

The time from one March equinox to the next, approximately 20 minutes shorter than a sidereal year.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the significance of Earth’s axis precession?

A

It changes the orientation of Earth’s axis and affects the locations of equinoxes and solstices, causing a 20-minute difference between tropical and sidereal years.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a planet’s synodic period?

A

The time from one alignment of a planet with the Sun in our sky to the next similar alignment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are conjunction and opposition in planetary motion?

A

Conjunction is when a planet aligns with the Sun, and opposition is when it is opposite the Sun in the sky.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Do Mercury and Venus ever appear directly in front of the Sun?

A

Yes, but only rarely during inferior conjunction, creating a transit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is apparent solar time?

A

Time based on the Sun’s actual position in the local sky, measured using a sundial.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is mean solar time?

A

An average time that accounts for variations in the solar day length, reading 12:00 at the average time the Sun crosses the meridian.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Fill in the blank: The length of a solar day varies throughout the year, averaging _____ hours.

A

24

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

True or False: The length of a sidereal year is longer than a tropical year.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does the term ‘sidereal’ refer to?

A

Related to the stars.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do we define a day in astronomical terms?

A

By Earth’s rotation, typically thought of as 24 hours but actually about 4 minutes short.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the average duration of a synodic month?

A

About 29.5 days.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What happens to the positions of the equinoxes and solstices over time?

A

They shift due to Earth’s precession, affecting the synchronization with the seasons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the length of the sidereal year?

A

About 365.25 days.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Fill in the blank: The apparent solar time is measured by the position of the Sun using a _____ .

A

sundial

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the difference between a solar day and a sidereal day primarily attributed to?

A

Earth’s orbit around the Sun requiring additional rotation to align with the Sun.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the significance of the Mayan calendar in relation to planetary periods?

A

It was based in part on the apparent motions of Venus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the average time between transits of Venus?

A

Pairs occur 8 years apart, with more than a century between the second of one pair and the first of the next.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the range of time a clock set to mean solar time may read compared to a sundial?

A

From about 17 minutes before noon to 15 minutes after noon

This corresponds to a range of times from 11:43 a.m. to 12:15 p.m.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is a major advantage of mean solar time over apparent solar time?
Mean solar time is more convenient because a reliable clock can always tell you the mean solar time ## Footnote Apparent solar time requires a sundial, which is not useful at night or in cloudy conditions.
26
How does mean solar time vary?
It varies with longitude due to Earth's rotation ## Footnote For instance, clocks in New York are 3 hours ahead of those in Los Angeles.
27
What significant change occurred on November 18, 1883, regarding timekeeping?
The railroad companies agreed to a new system that divided the United States into four time zones ## Footnote This led to the establishment of standard time.
28
What is standard time based on?
Standard time is generally the mean solar time in the center of a time zone ## Footnote Local mean solar time within a 1-hour-wide time zone typically does not differ by more than half an hour from standard time.
29
What is daylight saving time?
A time adjustment that is 1 hour ahead of standard time ## Footnote It is observed in most of the United States between the second Sunday in March and the first Sunday in November.
30
What is Greenwich Mean Time (GMT) commonly referred to in modern contexts?
Universal Time (UT) or Coordinated Universal Time (UTC) ## Footnote GMT is also known as 'Zulu time' in aviation.
31
What is the purpose of leap years in the calendar system?
To keep the calendar synchronized with the tropical year ## Footnote A leap year has 366 days, adding an extra day (February 29) every four years.
32
Who introduced the Julian calendar and when?
Julius Caesar in 46 B.C. ## Footnote The Julian calendar included the concept of the leap year.
33
What significant adjustment did Pope Gregory XIII make to the calendar in 1582?
He eliminated 10 days from October 1582, making October 15 the day after October 4 ## Footnote This adjustment realigned the calendar with the March equinox.
34
What is the exception to the leap year rule in the Gregorian calendar?
Leap years are skipped in century years unless the year is divisible by 400 ## Footnote For example, 2000 was a leap year, but 2100 will not be.
35
What coordinates are used to locate objects on the celestial sphere?
Declination (dec) and right ascension (RA) ## Footnote These coordinates are similar to latitude and longitude on Earth.
36
What is the celestial equator equivalent to on Earth?
Earth's equator ## Footnote Lines of declination are parallel to the celestial equator.
37
What does right ascension measure?
The angle measured in hours east of the March equinox ## Footnote A full circle of the celestial equator corresponds to 24 hours of right ascension.
38
What is the right ascension of the star Vega?
18 hours 35 minutes east of the March equinox ## Footnote This translates to about 279° east of the March equinox.
39
What is sidereal time?
Time based on the positions of stars relative to the meridian ## Footnote It differs from solar time, which is based on the Sun's position.
40
How is the hour angle (HA) defined?
The time since an object last crossed the meridian ## Footnote For example, if a star crossed the meridian 3 hours ago, its hour angle is 3 hours.
41
What is the relationship between right ascension and the meridian crossing time?
All objects with the same right ascension cross the meridian at the same time ## Footnote This means that right ascension helps predict when an object will be visible.
42
What is the hour angle (HA) of an object on the celestial sphere?
The time since it last crossed the meridian.
43
If a star crossed the meridian 3 hours ago, what is its hour angle?
-3 hours.
44
What is the local sidereal time (LST) based on?
The hour angle of the March equinox.
45
When is the local sidereal time 00:00?
When the March equinox is on the meridian.
46
What does the local sidereal time equal when stars are crossing the meridian?
The right ascension (RA) of those stars.
47
What is the relationship among an object's current hour angle, local sidereal time, and right ascension?
HA = LST - RA.
48
True or False: Sidereal clocks tick through 24 hours of sidereal time in one solar day.
False.
49
How much shorter is a sidereal day compared to a solar day?
About 4 minutes.
50
In the example, what is the local sidereal time if the solar time is 9:00 p.m. on the March equinox?
9 hours.
51
What does the Sun's right ascension change by approximately each month?
About 2 hours.
52
At the North Pole, what is the altitude of a star equal to?
Its declination.
53
What type of stars are circumpolar at the North Pole?
Stars north of the celestial equator.
54
What happens to stars with declination > 0° at the equator?
They rise north of due east and set north of due west.
55
At latitude 40°N, how is the altitude of the north celestial pole determined?
It is 40° above the horizon.
56
Fill in the blank: The celestial equator crosses the meridian at an altitude of _____ for any latitude.
90° minus your latitude.
57
What is the effect of Earth's varying orbital speed on solar days?
It can cause solar days to be longer or shorter than 24 hours.
58
What is an analemma?
A visual representation of the difference between apparent solar time and mean solar time.
59
What is the maximum difference between apparent solar time and mean solar time?
Up to 17 minutes.
60
What is the declination of the Sun at the March equinox?
0°.
61
What is the celestial equator's path through the local sky at any latitude?
It extends from due east to due west, crossing the meridian at an altitude of 90° minus latitude.
62
How does the declination of a star affect its path at different latitudes?
It determines the angle at which it rises and sets.
63
What happens to the length of a solar day around the times of the solstices?
It is slightly longer than average due to the Sun's motion being entirely eastward.
64
What can affect the actual length of a solar day?
Earth's varying orbital speed and the tilt of Earth's axis.
65
What are circumpolar stars at latitude 40°N?
Stars with declination greater than 40° ## Footnote These stars cross the meridian twice each day.
66
How do stars with declination greater than 0° behave at latitude 40°N?
They rise north of due east, set north of due west, and cross the meridian north of the celestial equator by an amount equal to their declination.
67
What is the altitude at which a star with declination greater than 20° crosses the meridian at latitude 40°N?
70° in the north ## Footnote This is because the star is 20° past the zenith.
68
What is the declination limit for stars to rise above the horizon at latitude 40°N?
Stars with declination less than -50° never rise above the horizon.
69
How do stars with negative declinations behave at latitude 40°N?
They rise south of due east, set south of due west, and cross the meridian south of the celestial equator.
70
What fraction of a star's daily circle is above the horizon if it lies on the celestial equator?
Exactly half ## Footnote This means they are above the horizon for about 12 hours.
71
How does the amount of time stars with positive declinations are above the horizon compare to those with negative declinations at latitude 40°N?
Stars with positive declinations are above the horizon for more than 12 hours, while those with negative declinations are above for less than 12 hours.
72
What is the Sun's path on the equinoxes at latitude 40°N?
The Sun rises due east, crosses the meridian at altitude 50° in the south, and sets due west.
73
At latitude 40°N, what is the altitude of the Sun at the June solstice?
Higher than 50° ## Footnote The exact altitude depends on the Sun's declination.
74
At latitude 40°N, what is the altitude of the Sun at the December solstice?
Lower than 50° ## Footnote This results in shorter daylight hours.
75
What special latitudes are defined by the Sun's path through the sky?
Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S)
76
What occurs at local noon on the June solstice at the Tropic of Cancer?
The Sun reaches the zenith.
77
What happens to the Sun's path at the Arctic Circle on the June solstice?
The Sun skims the northern horizon at midnight.
78
What is the latitude of the Arctic Circle?
66.5°N
79
How can you determine your latitude using Polaris?
By measuring the altitude of Polaris.
80
What does a measurement of Polaris at 17° indicate about your latitude?
Your latitude is between 16°N and 18°N.
81
How do you determine your longitude using local solar time?
By comparing it to Greenwich time.
82
If it is 1:00 p.m. locally and 3:00 p.m. in Greenwich, what is your longitude?
30°W
83
What is the effect of Earth's atmosphere on the visibility of the Sun at the poles?
It bends light, making the Sun appear slightly above the horizon even when it's below it.
84
What is the Sun's angular size effect when it sets?
It sets gradually rather than at a single moment.
85
What are the implications of the Sun's path for equatorial regions?
They do not have four seasons and experience rapid dawn and brief twilight.
86
What does longitude 30°W represent?
A specific position west of the Prime Meridian ## Footnote Longitude is measured in degrees east or west of the Prime Meridian.
87
How can you determine your longitude using local time?
By comparing your local time to the time in Greenwich ## Footnote If your local time is ahead of Greenwich, you are east; if behind, you are west.
88
What celestial object can help determine your longitude at night?
Stars ## Footnote You can compare the positions of stars in your local sky to their known positions at Greenwich.
89
What is an astrolabe?
A tool for measuring angles in the sky ## Footnote Invented by the ancient Greeks and improved by Islamic scholars.
90
What modern device is used for precise angle determinations in celestial navigation?
Sextant ## Footnote Incorporates a small telescope for sightings.
91
What is the difference between true north and magnetic north?
True north is geographic; magnetic north is influenced by Earth's magnetic field ## Footnote A compass points to magnetic north, which can differ from true north.
92
What do you need to navigate precisely with a compass?
A special map that accounts for local magnetic variations ## Footnote Magnetic maps are available at camping stores.
93
What celestial coordinates are important for navigation?
Coordinates of stars and the Sun ## Footnote Required to determine their paths through the local sky.
94
What is a cross-staff or Jacob's staff?
A simple tool for measuring angles in celestial navigation ## Footnote Used by medieval sailors as an alternative to astrolabes.
95
What is required to determine your longitude during the day?
A clock set to universal time ## Footnote Helps compare local apparent solar time to Greenwich time.
96
What historical problem did sailors face regarding longitude?
Difficulty determining longitude accurately before accurate clocks were invented ## Footnote Latitude was easier to determine than longitude.
97
What significant prize was offered by the British government in the 18th century?
A monetary prize for solving the problem of accurate longitude measurement at sea ## Footnote John Harrison won the prize in 1761.
98
How does the Global Positioning System (GPS) function?
Uses satellites to determine positions relative to Earth ## Footnote Satellites function like artificial stars, transmitting signals to receivers.
99
What is the risk to traditional celestial navigation methods today?
They are in danger of becoming a lost art due to GPS technology ## Footnote Amateur clubs are working to keep these skills alive.
100
Fill in the blank: An astrolabe's faceplate consists of a rotating star map and _______.
horizon plates for specific latitudes
101
True or False: Celestial navigation is less reliable than using a compass.
False ## Footnote Celestial navigation is generally more reliable for determining direction.

Astro 18 (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions