(E) Knowledge gaps PAPER 1 Flashcards
What is the lunar distance method?
It involves calculating the distance between the moon and a prominent star to find the navigator’s longitude.
What are some flaws of the lunar distance method?
- Depends on a clear sky
- Accurate measurements being taken at sea
- The Earth is NOT uniformly spherical
- Early tables had a larger margin of error than later versions
What’s the most prominent star(s) in Cygnus?
Deneb
What’s the most prominent star(s) in Crux?
Mimosa, Acrux
What’s the most prominent star(s) in Cassiopeia?
Schedar
What’s the most prominent star(s) in The summer triangle?
Deneb, Vega and Altair
What’s the most prominent star(s) in The great square of Pegasus?
Alpheratz
What’s the most prominent star(s) in The Plough?
Dubhe
How many degrees is the Earths axis tilted to the ecliptic by?
23.5 degrees
What is the First point of Libra?
The point at which the sun on the ecliptic crosses the celestial equator at the autumnal equinox
What is the First point of Aries?
The point at which the sun on the ecliptic crosses the celestial equator at the vernal equinox
How can we work out the sun’s altitude?
Sun Altitude = Sun Declination + (90° - Latitude of Observer)
What’s the equatorial coordinate system?
RA and Declination
What’s the horizontal coordinate system?
Altitude and Azimuth
How many constellations does the sun cross in a year?
13
Difference between Meteor, Meteoroid, Meteorite?
Meteor: In space
Meteoroid: In atmosphere
Meteorite: On Earth
Where are star maps usually found?
Star maps and charts are published in books, newspapers and magazines
How are brighter/smaller stars presented on star maps?
brighter stars = larger dot
smaller stars = smaller dot
What is the purpose of a planisphere?
To find out what stars are viewable at any time
What is the structure of a planisphere?
Two discs fastened to each other
Top disk:
—-> On one of them is a hole (so that a portion of the disc underneath can be seen)
—-> Around the edge are hours of the day
Underneath disk:
—-> A star map showing every constellation available for viewing from a general location
What does the edge of the round area represent on a planisphere?
The horizon
What are the two discs fixated at on a planisphere?
The pole axis
How would you use a planisphere?
- To find the stars available on 4th September at 10pm you would move the hour dial that says 10pm on the overlay next to the date on the underlay
- Point the planisphere north
