How far away are the stars
Download
1 / 21

How Far Away Are The Stars? - PowerPoint PPT Presentation


  • 114 Views
  • Uploaded on

How Far Away Are The Stars?. Distances in the Solar System. Kepler’s Third Law relates period and distance Defines a relative distance scale One accurate distance determines everything. The Streetlight Analogy: What can the prisoner learn about the outside world?. Parallax.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'How Far Away Are The Stars?' - tacita


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Distances in the solar system
Distances in the Solar System

  • Kepler’s Third Law relates period and distance

  • Defines a relative distance scale

  • One accurate distance determines everything


The streetlight analogy what can the prisoner learn about the outside world
The Streetlight Analogy: What can the prisoner learn about the outside world?


Parallax
Parallax

  • Nearby Lights Appear to Change Position as the Observer Moves

  • Can Triangulate to get distance

  • Can determine true brightness of lights


Parallax and the distances of stars
Parallax and the Distances of Stars

  • Stars appear identical all over Earth

  • They do show slight parallax shift from opposite sides of Earth’s orbit


Parallax pre 1997
Parallax: pre-1997

  • Parallax is tiny - was once used as argument against motion of the Earth

  • One second of arc = size of a quarter at 5 km (3 mi.)

  • Parallax angle of nearest star (4.3 l.y.) is 0.75”

  • Accuracy limited by Earth’s atmosphere

  • Fairly accurate to 30-40 l.y., rough to 100


Hipparcos
Hipparcos

  • Named for ancient Greek astronomer who catalogued the stars

  • High Precision Parallax Collecting System

  • Launched by European Space Agency, 1989

  • Data Collection 1989-1993

  • Data Analysis 1993-1997


The hipparcos data
The Hipparcos Data

  • 118,218 stars measured: parallax and motion

  • 22,396 accurate to 10% - a 20-fold improvement

  • Stars out to 200-300 l.y. are known to within 10%

  • 30,000 more accurate to 20%

  • All pre-Hipparcos distance data is obsolete


Gaia the next generation
GAIA: the Next Generation

  • To be placed in Earth-Sun L2 point

  • Measure a billion stars out to 100,000 l.y.- 1% of entire galaxy

  • Transmit 1 Mb every 8 seconds for five years

  • Accuracy of five micro-seconds (width of a human hair at 2,500 miles)

  • Data could be available by 2020


Beyond parallax
Beyond Parallax

  • More Distant Lights Show Little Parallax

  • We know how much light nearby lights emit

  • Can use this to estimate distance of faraway lights


How far away are the stars


How far away are the stars


How far away are the stars


How far away are the stars


Disasters
Disasters is, we can estimate the distance to faraway cities

  • Sometimes a big fire will outshine the rest of the city

  • Distant fires can be used as distance estimators

  • Sometimes a fire is visible even if the city is too faint to see


The cosmic distance scale
The Cosmic Distance Scale is, we can estimate the distance to faraway cities

  • Makes use of different indicators for different distances

  • Each increase in distance builds on previous distances

  • Faraway distances are only as accurate as nearer distances


Distances in our galaxy
Distances in our Galaxy is, we can estimate the distance to faraway cities

  • Parallax (to 300+ l.y. with Hipparcos)

  • Spectroscopic Parallax (Brightness of stars of known types and absolute brightness)

  • Moving Cluster Method

    • Radial motions of stars from Doppler Effect

    • Transverse motions measured directly

    • Assume velocity distribution uniform


Spectroscopic parallax
Spectroscopic Parallax is, we can estimate the distance to faraway cities


Variable stars
Variable Stars is, we can estimate the distance to faraway cities

  • Henrietta Leavitt, 1917

  • Measured Magellanic Cloud stars - a lot in a small space

  • Unexpected discovery- some variables have uniform properties

  • Magellanic Cloud stars all about same distance away (170,000 l.y.)


Variable stars as yardsticks
Variable Stars as Yardsticks is, we can estimate the distance to faraway cities

  • RR Lyrae Stars

    • Have distinctive light variation curve

    • All about 100 times as luminous as Sun

  • Cepheid Variables

    • The brighter, the longer the period

    • Think of a bell ringing


Extragalactic yardsticks standard candles
Extragalactic Yardsticks (“Standard Candles”) is, we can estimate the distance to faraway cities

  • Cepheids (Governed specifications for Hubble Space Telescope)

  • Supernovae

  • Brightest Galaxy in Cluster

  • Hubble Parameter (25 km/sec/m.l.y. - implies age of universe = 12 billion years)