6 Celestial Observation

Question 1

How many constellations are there?

Answer 1

88 constellations

Question 2

What are asterisms?

Answer 2

Asterisms are unofficial, popular patterns of bright stars that have a close likeness to their name. Examples include ‘The Plough’ in Ursa Major or Orion’s Belt

Question 3

What is an open cluster of stars? (Give an Example)

Answer 3

A group of stars that are roughly the same age and formed in the same giant molecular cloud. An example is the Pleiades

Question 4

What are constellation pointers? (Give an Example)

Answer 4

Pointers from constellations that point to another star or celestial object. An example is The Plough which points to Polaris and the ‘handle’ arc to Arcturus

Question 5

What is an optical double star?

Answer 5

Two stars that appear to have merged from our perspective

Question 6

What is declination?

Answer 6

Declination is the projection of latitude onto the celestial sphere; it is measured in degrees (+&-signs indicate N or S)

Question 7

What is Right Ascension?

Answer 7

Right Ascension is the East-to-West coordinate system. Right ascension is measured from the first point of Aries; it is measured in hours and minutes where 1 hr=15° and 1 min=0.25°

Question 8

What is Azimuth?

Answer 8

The Azimuth is a bearing from due north moving round eastwards to the point on the observer’s horizon directly under the star; it ranges from 0° to 360° back to 0° again

Question 9

What is Zenith and Nadir?

Answer 9

The Zenith is the point directly above the observer

The Nadir is the point directly below the observer

Question 10

What is your Meridian?

Answer 10

Your Meridian is the great arc passing through the celestial poles, as well as the zenith and nadir of an observer’s location.

Question 11

What is Diurnal Motion?

Answer 11

Diurnal motion is when a star reaches its highest point (culminate) when they are due south as they cross the observer’s meridian and later set in the west.

Question 12

How long does it take for the Earth to rotate once?

Answer 12

23hrs 56 mins

Question 13

What is a Sidereal day?

Answer 13

A sidereal day is how long it takes for the Earth to rotate in accordance with the stars

Question 14

What is a Solar Day?

Answer 14

A Solar Day is the time it takes for the Earth to rotate around its axis so the Sun appears in the same position in the sky

Question 15

How long is a Solar Day?

Answer 15

24 hrs

Question 16

Why does a Solar day occur?

Answer 16

A Solar day occurs because, during the time it takes for the Earth to rotate 360°, the Earth also moves around the Sun by 1° so it needs to rotate for a further 4 mins to align back to the same point as the Sun

Question 17

How can you tell the local sidereal time (LST) using Right Ascension?

Answer 17

Local Sidereal time is the time the Right Ascension of a star that lies on the observer’s meridian at a given moment in time. An example is if a star with RA= 14 h 45 mins lies on an observers meridian, the LST is 14:45

Question 18

What is a star’s hour angle?

Answer 18

A star’s hour angle is the time since the celestial object was last crossing the observers meridian
or
the angular distance on the celestial sphere measured westward along the celestial equator from the meridian to the hour circle passing through a point

Question 19

How do you calculate a star’s hour angle?

Answer 19

Hour Angle = Local Sidereal Time - Right Ascension

Question 20

What does the Hour Angle tell you?

Answer 20

If the Hour Angle is negative, its value tells an astronomer how long it will take before the star or celestial object will be crossing their meridian

Question 21

What is the NCP?

Answer 21

The NCP is the North Celestial Pole. It is the equivalent of a North Pole in the celestial sphere. Polaris is located within 0.8° of the NCP

Question 22

What is Altitude?

Answer 22

The Altitude of a star measures the angle between the horizon, you, and the celestial object

Question 23

What is the Celestial Equator?

Answer 23

The Celestial Equator is the hypothetical sphere which contains the stars ‘painted’ on the inside

Question 24

What is the Ecliptic?

Answer 24

The Ecliptic is an imaginary circle on the Celestial Sphere that represents the apparent path of the Sun during the year.

Question 25

How can you work out the observer’s latitude?

Answer 25

Altitude of NCP (or SCP) = observer’s latitude

Altitude of Polaris = observer’s latitude

Question 26

What is Polar Distance?

Answer 26

Polar Distance is the angular distance of a star from the NCP

Question 27

How do you work out Polar Distance?

Answer 27

Polar Distance = 90° - Declination

Question 28

How can you also figure out polar distance?

Answer 28

The small circle that a star traces out during a sidereal day has a radius equal to its polar distance

Question 29

What is Upper Transit?

Answer 29

When a celestial body passes your meridian at its highest point. The Upper Transit is when a star culminates

Question 30

What is Lower Transit?

Answer 30

Lower transit is when a celestial body passes your meridian at its lowest point

Question 31

How can you calculate altitude?

Answer 31

Altitude = Latitude ± Polar Distance

at upper and lower transits

Question 32

What are Circumpolar Stars?

Answer 32

Circumpolar stars are stars the remain visible at all times and do not set below the horizon

Question 33

How can you determine if a star is circumpolar?

Answer 33

For a star to be circumpolar:

90° - Declination < latitude of the observer

Question 34

What does Orion’s belt point to?

Answer 34

Towards the left, it points to Sirius. To the right, it points to Aldebaran then the Pleiades.

Question 35

What does the Square Of Pegasus point to?

Answer 35

It points to the Andromeda Galaxy and Fomalhaut

Question 36

How can you describe a meteor when viewed?

Answer 36

A short, bright streak of light in the sky, lasting a few seconds

Question 37

What do nebulae look like when observed?

Answer 37

A fuzzy patch of light

Question 38

What does the aurora look like to the naked eye?

Answer 38

A curtain or stream of of coloured light

Question 39

Why would greatest elongation be the best position to observe an inferior planet?

Answer 39

The angle between the planet and the Sun is large. This means the planet is in a darker area of sky so contrast is greater

Question 40

What is the diameter of the Milky Way galaxy?

Answer 40

30 kpc

Question 41

Name four types of galaxies:

Answer 41

Elliptical
Barred Spiral
Spiral
Lenticular
Peculiar
Dwarf Elliptical
Quasar

Question 42

What are binary stars?

Answer 42

2 stars the orbit around the mutual centre of gravity

Question 43

What is a double star?

Answer 43

2 stars that appear as one when viewed

Question 44

What are variable stars?

Answer 44

Stars that change brightness

Question 45

Name a reason why its difficult to view the sky.

Answer 45

Any one from:

• We’re restricted to view only at night
• The atmosphere continuously rises and falls; this causes the stars to ‘twinkle’
• Skyglow; an orange haze cast by lights near urban places
• ‘Glare’ from lights that ruins our dark adaption

Question 46

What are the Van Allen Belts?

Answer 46

The Van Allen belts are regions with intense radiation.
The Inner belt consists of high energy protons.
The Outer belts are high energy electrons that dip toward the poles.

Question 47

How do you calculate your latitude?

Answer 47

Measure the angle from your zenith to the Sun.

Add the angle from your zenith to the Sun at the equator for this specific day

Question 48

What are seasonal constellations?

Answer 48

Seasonal constellations are the Constellations that can only be seen in certain times of the year as the Sun blocks us from viewing them when the Sun covers it up