Section 3: Stars Flashcards
Constellations
Area of sky containing a pattern of stars
Double stars
Look like close pairings of stars
Asterism
Smaller groups of stars that form familiar shapes
Appearance of nebulae
Fuzzy patches of light
Open clusters
Collection of stars linked gravitationally
Draw the plough and its pointers
Arcturus - follow arc
Polaris - follow right hand edge vertically
Draw Orion and its pointers
Sirius - follow Orion’s Belt to the left
Aldebaran - follow Orion’s Belt to the right
The Pleiades - beyond Aldebaran
Draw Cygnus
Cross
Draw Cassiopeia
W
Draw Pegasus and its pointers
Formalhaut - down from right hand edge Andromeda galaxy (M31) - follow top stars up to the left
Why are some constellations visible all year and others are seasonal
Seasonal - Earths orbital motion around the sun and stars cannot be seen during the day
Right ascension
Equivalent to longitude but in the night sky
Zero right ascension is point on celestial sphere at which sun moves from S to N hemisphere
Expressed in hours and minutes E to the left on a star chart
1 hour = 15 degrees
Declination
Equivalent to latitude but in the night sky
What’s the declination of Polaris and why does it appear fixed in the night sky
90 degrees N = +90 degrees declination
Circumpolar
Elevation of Polaris above horizon = latitude of observer
When will a star be circumpolar from a given latitude
Declination > 90 - latitude
Zodiacal band on star chart
Straddles ecliptic by 8 degrees on either side
Culminate
Due south
Highest in the sky
Cross observers meridian
Messier catalogue
“Fuzzy” objects many of which are just vis. with naked eye
Contains over 100 examples of star clusters, nebulae and galaxies
Was made to avoid confusion with comets
Optical double stars vs binary stars
Optical double stars - only appear to be closely aligned
Binary system - same distance from us and orbit their common centre of gravity
Magnitude classes
Observed brightness of a star
Smaller number = higher brightness
Diff. in 5 magnitudes corresponds to 100x brighter
Describe heliocentric parallax to obtain distances
Method to determine distance to nearby star by using shift in position against bg of distant stars as earth orbits sun
Relationship of distance and parallax angle
d = 1/p
One parsec
The distance at which a star would have a parallax angle of one arcsec
Absolute magnitude
The apparent magnitude a star would have if observed from a distance of 10 parsecs
Formula relating apparent and absolute magnitude
M = m + 5 - 5log(d) d = distance in pc M = absolute magnitude m = apparent magnitude
What are the two main classes of variable star
Binary stars
Cepheid variable stars
Light curve for a Cepheid variable star
Sharp rise and slower decay as it expands and contracts
What information can be obtained from a spectrum
Chemical composition
Temperature
Radial (in line of sight) velocity from Doppler shift
What spectral class is our sun
G2
Order of spectral type and relation to temperature
O B A F G K M
Hot -> Cool
Sketch Hertzsprung-Russell diagram
Luminosity/Spectral type
See page 54
What is a nebula
Large cloud of dust and gas
Site of star formation
What’s a planetary nebula
When the helium fuel is depleted from a red giant and it loses its outer layers in an expanding shell of gas
Pulsar
Rotating neutron stars emit intense radio waves from their polar regions
