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Astronomy > Section 3: Stars > Flashcards

Section 3: Stars Flashcards

0
Q

Constellations

A

Area of sky containing a pattern of stars

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1
Q

Double stars

A

Look like close pairings of stars

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2
Q

Asterism

A

Smaller groups of stars that form familiar shapes

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3
Q

Appearance of nebulae

A

Fuzzy patches of light

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4
Q

Open clusters

A

Collection of stars linked gravitationally

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5
Q

Draw the plough and its pointers

A

Arcturus - follow arc

Polaris - follow right hand edge vertically

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6
Q

Draw Orion and its pointers

A

Sirius - follow Orion’s Belt to the left
Aldebaran - follow Orion’s Belt to the right
The Pleiades - beyond Aldebaran

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7
Q

Draw Cygnus

A

Cross

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8
Q

Draw Cassiopeia

A

W

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9
Q

Draw Pegasus and its pointers

A 
Formalhaut - down from right hand edge
Andromeda galaxy (M31) - follow top stars up to the left
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10
Q

Why are some constellations visible all year and others are seasonal

A

Seasonal - Earths orbital motion around the sun and stars cannot be seen during the day

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11
Q

Right ascension

A

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

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12
Q

Declination

A

Equivalent to latitude but in the night sky

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13
Q

What’s the declination of Polaris and why does it appear fixed in the night sky

A

90 degrees N = +90 degrees declination
Circumpolar
Elevation of Polaris above horizon = latitude of observer

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14
Q

When will a star be circumpolar from a given latitude

A

Declination > 90 - latitude

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15
Q

Zodiacal band on star chart

A

Straddles ecliptic by 8 degrees on either side

16
Q

Culminate

A

Due south
Highest in the sky
Cross observers meridian

17
Q

Messier catalogue

A

“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

18
Q

Optical double stars vs binary stars

A

Optical double stars - only appear to be closely aligned

Binary system - same distance from us and orbit their common centre of gravity

19
Q

Magnitude classes

A

Observed brightness of a star
Smaller number = higher brightness
Diff. in 5 magnitudes corresponds to 100x brighter

20
Q

Describe heliocentric parallax to obtain distances

A

Method to determine distance to nearby star by using shift in position against bg of distant stars as earth orbits sun

21
Q

Relationship of distance and parallax angle

A

d = 1/p

22
Q

One parsec

A

The distance at which a star would have a parallax angle of one arcsec

23
Q

Absolute magnitude

A

The apparent magnitude a star would have if observed from a distance of 10 parsecs

24
Q

Formula relating apparent and absolute magnitude

A 
M = m + 5 - 5log(d)
d = distance in pc
M = absolute magnitude
m = apparent magnitude
25
Q

What are the two main classes of variable star

A

Binary stars

Cepheid variable stars

26
Q

Light curve for a Cepheid variable star

A

Sharp rise and slower decay as it expands and contracts

27
Q

What information can be obtained from a spectrum

A

Chemical composition
Temperature
Radial (in line of sight) velocity from Doppler shift

28
Q

What spectral class is our sun

A

G2

29
Q

Order of spectral type and relation to temperature

A

O B A F G K M

Hot -> Cool

30
Q

Sketch Hertzsprung-Russell diagram

A

Luminosity/Spectral type

See page 54

31
Q

What is a nebula

A

Large cloud of dust and gas

Site of star formation

32
Q

What’s a planetary nebula

A

When the helium fuel is depleted from a red giant and it loses its outer layers in an expanding shell of gas

33
Q

Pulsar

A

Rotating neutron stars emit intense radio waves from their polar regions

Astronomy (4 decks)

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