Topic 6 (Celestial Observations) Flashcards
What constellations do you need to recognise
Cassiopeia Cygnus Orion Plough Southern cross Summer Triangle Square of Pegasus (Look at constellations poster for diagrams)
What is a constellation
A section of the sky with stars bearing no resemblance to their name
What is an asterism
An asterism is an UNOFFICIAL set of stars that do bear close likeness to there name such as Orión’s belt
What do planets slowly move across night after night
The zodiacal band
What are the northern and southern lights at the poles called
Aurora borealis and aurora australis
What does a supernova look like to the naked eye
A sudden appearance of a bright star that very slowly fades
Comets are rare and appear as an…
Extended fuzzy object with one or two tails
What do many asterisms contain
Pointers that lead to a specific object in the sky such as the Big Dipper and Polaris
What is the celestial sphere
An imaginary sphere concentric its earth that acts as a similar system as latitude and longitude on earth but for space
What is the ecliptic on the celestial sphere
A line around the earth that maps the suns path over a year
What is the first point of Aries on the celestial sphere
where the ecliptic cuts across the celestial equator as it moves from south to north
What is the equatorial co-ordinate system
A co-ordinate system for space in which latitude and longitude are replaced by declination and right ascension
What is declination
Declination is the projection of latitude onto the celestial sphere
(- and + are equal to south and north)
What is right ascension
Right ascension is measured eastwards form the first point of Aries it’s is measured in hours where and hour = 15 degrees
What is the horizontal co-ordinate system
A more user friendly co-ordinate system using azimuth and Altitude instead of latitude and longitude
What is azimuth
A simple bearing measured in degrees from due north (geographical) moving round eastwards to the point on the observers horizon directly under the star ,it ranges from 0 to 360 degrees
What is altitude
Found by the angle from the observers horizon upwards to the star or other celestial object; it ranges from 0 to 90 degrees( the observers zenith)
What is a sidereal day
How long it takes the earth to rotate 360degrees which takes (23hrs 56mins)
What is a solar day
A solar day is a sidereal day + another 4 mins for the earth to align a given point on the surface with the sun.therefore It follows that the stars rise reach their highest point and set 4 minutes earlier each day
What is local sidereal time
Local sidereal time is the right ascension of a star on the observers meridian - remember right ascension is measured in hours
Observers often use hour angle what is it
Hour angle is the time in hours and mins since the object was last crossing over the meridian
If hour angle is negative it tells how much time before the star or other celestial object will cross their meridian
What is polar distance
Polar distance is a useful measure of the angular distance of a celestial object from the NCP since the declination of the NCP is +90 it follows that
Polar distance =90degrees - declination
What is a circumpolar star
When a stars polar distance is so small it remains visible all the time
What makes a star circumpolar
For a star to be circumpolar, it’s polar distance must be less than the altitude of NCP(equal to the observers latitude)
For a star to be circumpolar equation
90degrees - declination < latitude of the observer
Example (circumpolar equation)
Thunan (dec=+64degrees) is circumpolar from ulaanbaatar (lat 48degrees) because 90-64=26<48
When is the best time to observe a celestial objects with the naked eye
When it approaches culmination (their highest point)
What must the eye be before any naked eye observing can be done
Dark adapted (this takes about 20-30mims of darkness)
How should you look at faint objects such as the andromeda galaxy
Use averted vision (looking slightly to the side of it) as it is necessary to stimulate the rods to see this and not the cones
What factors affect naked eye observing
.light pollution .landscape .cloud .transparency(recent rain removes dust) Steadiness of the atmosphere (measured from I-V on the Antoniadi scale)
What are the prominent stars of Cygnus the swan
Deneb, top right
What are the significant stars of Cassiopeia
Schedar
What are the significant stars of the southern cross
Mimosa, left
Acrux, bottom
What are the significant stars in the Summer Triangle asterism
Deneb, top left
Vega, top right
Altair, bottom
What stars con be found from pointers in the Big Dipper
Arcturus, follow the handle
Polaris, follow the line from the two end stars upwards
What stars can be found from following the Great square of pegasus
Fomalhaut, follow the right two stars down
