(E) Topic 6 - Celestial Observation

Question 1

What is the definition of Celestial sphere?

Answer 1

An imaginary sphere around Earth where all the celestial objects lie

Question 2

What is the definition of Celestial poles?

Answer 2

Earth’s poles that are projected outwards to the sky

Question 3

What is the definition of Celestial equator?

Answer 3

Earth’s equator that is projected outwards to the sky

Question 4

What is the definition of Zenith?

Answer 4

The Zenith is the point directly above the observer’s head. 90° perpendicular to the ground.

Question 5

What is the definition of Culmination?

Answer 5

The star is at its greatest altitude and therefore highest in the sky (potentially the best time to observe)

Question 6

What is the definition of Circumpolarity?

Answer 6

When a star never sets below the horizon from a certain latitude.

Question 7

What is the definition of Cardinal points?

Answer 7

One of the four main points of the compass

Question 8

What are the factors affecting visibility? (and some examples of each)

Answer 8

• Rising and setting
• Seeing conditions (steadiness of the atmosphere)
• Transparency of the atmosphere (recent rain removes dust particles)
• Weather conditions (presence of cloud)
• Landscape (trees and high buildings)

Question 9

Cones are sensitive to…

Answer 9

Colour (when the light is bright enough)

Question 10

Rods are sensitive to…

Answer 10

Light intensity

Question 11

Name 2 naked eye techniques

Answer 11

Averted vision and dark adaptation

Question 12

How long does it usually take for eyes to become dark-adapted?

Answer 12

20-30 minutes

Question 13

What is averted vision?

Answer 13

Looking slightly to the side of the object

Question 14

Why do we use averted vision?

Answer 14

CONES ARE NOT ACTIVATED IN DIM LIGHT

The rod cells in our eyes are located on the outside of the optical axis. If we look slightly to the side of an object, it allows light to fall onto the rods and the object can be seen better.

Question 15

What is dark adaptation ideal for?

Answer 15

Night vision

Question 16

When is the best time to observe celestial objects?

Answer 16

When close to culmination

Question 17

Which scale is seeing conditions measured by?

Answer 17

The Antoniadi Scale

Question 18

What is the definition of a star’s hour angle?

Answer 18

The time (in hours and minutes) since the object was last crossing the observers meridian

Question 19

Equation for calculating hour angle

Answer 19

Hour angle = local sidereal time - right ascension

Question 20

What is the local sidereal time of an observer equivalent to?

Answer 20

The right ascension of a star that lies on the observers meridian at a given moment in time

Question 21

Whats NCP/SCP an abbreviation of?

Answer 21

Northern/Southern Celestial Pole

Question 22

Altitude of NCP is equal to…
And what does this mean with Polaris?

Answer 22

Altitude of NCP/SCP = observers latitude

Therefore

Altitude of Polaris = observers latitude

Question 23

What’s the definition of a star’s polar distance?

Answer 23

The angular distance of a star from the NCP

Question 24

What is polar distance also known as?

Answer 24

Co-declination

Question 25

What’s the declination of the NCP?

Answer 25

+90 degrees

Question 26

How do you calculate polar distance?

Answer 26

Polar distance = 90 degrees - declination

Question 27

What are upper and lower transit?

Answer 27

The points at which a star crosses the local meridian

Question 28

Upper transit is also when a star…

Answer 28

Culminates

Question 29

Diurnal

Answer 29

Daytime

Question 30

Nocturnal

Answer 30

Nighttime

Question 31

In what direction do the Sun and stars appear to move across the sky?

Answer 31

In an east to west direction

Question 32

In what direction does the Earth rotate?

Answer 32

Anti-clockwise (west to east direction)

Question 33

What is the hour angle calculation used to determine?

Answer 33

Shows how long it will take for a star to transit your local meridian