Celestial Observation Flashcards
(45 cards)
Recognise Cassiopeia
Flat W
Recognise Cygnus
Winged Cross(swan), Deneb is top star, Glenah on the left
Recognise Orion
Three central stars in the belt. Points upwards to Aldebaran and downwards to Sirius. Nebula is contained in bottom half
Recognise the Plough
Looks like a Saucepan. Follow curve to Arcturus, follow other edge up to Polaris
Recognise Southern Cross
A cross of the stars Gacrux and Acrux top and bottom and Mimosa and Palida left and right
Summer Triangle
A triangle of the stars Deneb, Vega and Altair
Square of Pegasus
Square of stars Sheet, Markab, Algenub and Alpheratz with trailing arms
Follow bottom line upwards to Andromeda
Causes and effects of light pollution
Caused by urban areas and means that higher magnitude bodies are no longer visible
Also caused by the Sun and Moon
Describe the meanings of the celestial sphere, celestial poles, and celestial equator
The celestial sphere is the imaginary sphere that we look out onto as the night sky, The celestial poles are the same as real poles, as is the celestial equator
Describe the equatorial coordinate system
In which latitude and longitude are declination (dec) in degrees and Right Ascension (RA) in hours and minutes, It does not depend on an observers coordinates, simply imagine the lines of latitude and longitude extrapolated onto the night sky
Describe the horizon coordinate system
This measures Azimuth as a bearing in degrees from north, eastwards to directly under the star
At altitude, the angle of the star above the horizon. It is completely dependent on the observers coordinates.
How does the observers latitude link the two co-ordinate systems for a object on the observers meridian
Declination of object = Angle - Altitude of Celestial Equator
Declination of object = Angle - (90-Lat)
Altitude of Celestial equator = 90-lat
How does the observers meridian define local sidereal time and hour angle
Local sidereal time is the RA of an object on the observers meridian
Hour angle is the time since an object was on the observers meridian. If it is negative, it is the amount of time until the object will be on the meridian
Hour angle is= LST - RA
When is the best time to view a celestial object
It is best to view objects when they are crossing the meridian, in other words RA = LST
The best objects to view are those with a higher declination, as they will have a higher altitude at culmination.
Define Cardinal Points
The directions (N, S, E, W) when projected onto the celestial sphere
Define culmination
The point at which stars are at their highest altitude
Define Meridian
The imaginary line due south and north of the observer
Define zenith
The point in the sky directly above an observer
Define circumpolar
A star that does not set
Describe the diurnal motion of the sky
Caused by the Earths rotation, causing stars to rise in the east and set in the west like the sun
How does a stars declination show circumpolarity
For circumpolar stars : 90-dec < Observers latitude
