(E) Topic 6 - Celestial Observation Flashcards
What is the definition of Celestial sphere?
An imaginary sphere around Earth where all the celestial objects lie
What is the definition of Celestial poles?
Earth’s poles that are projected outwards to the sky
What is the definition of Celestial equator?
Earth’s equator that is projected outwards to the sky
What is the definition of Zenith?
The Zenith is the point directly above the observer’s head. 90° perpendicular to the ground.
What is the definition of Culmination?
The star is at its greatest altitude and therefore highest in the sky (potentially the best time to observe)
What is the definition of Circumpolarity?
When a star never sets below the horizon from a certain latitude.
What is the definition of Cardinal points?
One of the four main points of the compass
What are the factors affecting visibility? (and some examples of each)
- 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)
Cones are sensitive to…
Colour (when the light is bright enough)
Rods are sensitive to…
Light intensity
Name 2 naked eye techniques
Averted vision and dark adaptation
How long does it usually take for eyes to become dark-adapted?
20-30 minutes
What is averted vision?
Looking slightly to the side of the object
Why do we use averted vision?
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.
What is dark adaptation ideal for?
Night vision
When is the best time to observe celestial objects?
When close to culmination
Which scale is seeing conditions measured by?
The Antoniadi Scale
What is the definition of a star’s hour angle?
The time (in hours and minutes) since the object was last crossing the observers meridian
Equation for calculating hour angle
Hour angle = local sidereal time - right ascension
What is the local sidereal time of an observer equivalent to?
The right ascension of a star that lies on the observers meridian at a given moment in time
Whats NCP/SCP an abbreviation of?
Northern/Southern Celestial Pole
Altitude of NCP is equal to…
And what does this mean with Polaris?
Altitude of NCP/SCP = observers latitude
Therefore
Altitude of Polaris = observers latitude
What’s the definition of a star’s polar distance?
The angular distance of a star from the NCP
What is polar distance also known as?
Co-declination
What’s the declination of the NCP?
+90 degrees
How do you calculate polar distance?
Polar distance = 90 degrees - declination
What are upper and lower transit?
The points at which a star crosses the local meridian
Upper transit is also when a star…
Culminates
Diurnal
Daytime
Nocturnal
Nighttime
In what direction do the Sun and stars appear to move across the sky?
In an east to west direction
In what direction does the Earth rotate?
Anti-clockwise (west to east direction)
What is the hour angle calculation used to determine?
Shows how long it will take for a star to transit your local meridian
