Transcript Groups_of_Stars_spectra

Measuring Stars
Visible Spectrum & Wavelengths
Spectral
Types
• Continuous spectrum: Produced when white light passes
through a prism
• Emission spectra: Produced from a heated gas giving off
light
• Absorption spectra: Produced when white light passes
through a cool gas
Spectra & Star Composition
• Can tell a star’s composition by looking at
its spectra (usually an absorption spectra)
• We can identify the spectra of various
elements
• Comparing a stars absorption spectra to
the elements can indicate composition
Spectra & Star Composition
Spectral Lines of a Star
Dopplar/Wavelength Shifts
In space there is no up down left or right,
only towards or away
• Motion towards & away causes the light given off
to be squeezed or stretched
• Blue-shift: wavelengths from objects moving
toward another get squeezed
• Red-shift: wavelengths from objects moving
away get stretched
Wavelength Shifts
Groups of Stars
&
Judging Distance in Space
Constellations
• Stars named after animals, mythical
characters, & everyday objects
1. 88 constellations named by ancient people
2. Circumpolar stars: can be seen all year long
depending on the hemisphere you live
• Stars may not actually be close to each
other in space
Constellations
Ursa Major (Big Dipper)
Cygnus The Swan
Star Clusters & Binaries
Pleiades Cluster
Arches Cluster
Binary System
• Clusters: Stars actually close to each other & held close
by their gravity
– Open clusters: stars NOT densely packed
– Globular Cluster: stars ARE densely packed
• Binaries: Stars that come in pairs orbiting a center of
mass (over ½ of all stars)
Judging Distances: Parallax
• Parallax: apparent change in a star’s position
compared to background stars
• More apparent change = closer the star is
Units of Distance
• Astronomical Unit (AU): average distance
from Sun to Earth (93 million miles)
• Light Year (ly): distance light travels in one
year (~9.5 trillion km, or 5.9 trillion mi)
• Parsec (pc): it is equal to 3.26 ly
Basic Properties of Stars
• Magnitude: general brightness of a star
– Ranked using + & - numbers
– A +1 is 100x’s brighter than a +6
– Brightest stars have negative magnitude numbers
• Apparent Magnitude: brightness as it appears
from Earth
• Absolute Magnitude: brightness of a star from
10 parsecs
• Luminosity: amount of energy output from the
surface (very similar to brightness)
Magnitude Comparison