Measuring the Stars (Part I). 3-D Positions in Space of the Stars Closest to our Sun:

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Presentation transcript:

Measuring the Stars (Part I)

3-D Positions in Space of the Stars Closest to our Sun:

Nearby Star Systems in Culture & Science Fiction:

3-D Positions in Space of the Stars Closest to our Sun:

To Measure “Radial Motion” of Stars (towards/away from us)… …but how to determine a Star’s “Tangential” (sideways/perpendicular) Motion?? Use Doppler Shifts! The “Fix’d Stars”… …do they move? Of Course They do! (but FAR Away, their Sky Positions appear to change slowly!)

Barnard’s (“Runaway”) Star – The Largest “Proper Motion” in our sky! (~10’’/yr)

Anything else “Unusual” about Alpha Centauri…?  It’s a Triple (Multiple) Star! …only ~1/3 of “Sun-like” stars are Single Stars!

Some apparent “multiple” stars are just “Optical Doubles” (Astronomical illusions…)

Others really are Multiple Star Systems (“Binary Stars”, “Triples”, “Quadruples”…)

Some Multiple Star Systems can even Host Exoplanets!

Some Multiple Stars can be Visually Separated…

…and some Multiples cannot be visually separated… (“Spectroscopic Binaries”)

Stellar Size: How Big is the Sun? (…as Stars go…)

Link to Video, “Star Size Comparison”, (Featuring music from “Alien”, “The Black Hole”, and “Bladerunner”)

What does a picture of a Star look like, so far away? (Just a “point of light”?)

How to find the size of a star that’s so far that it looks Point-like? Proportionality for Luminosity: T = Star’s Surface Temperature, R = Radius of Star, L = Star’s Luminosity.

What affects a star’s Apparent Brightness, besides Radius & Temp? Proportionality for Apparent Brightness (“Flux”): T = Star’s Surface Temperature, R = Radius of Star, L = Star’s Luminosity, D = Distance to the Star.

The “Apparent Magnitude” Scale (as seen from Earth) Mag. Scale “Oddities”: Brighter = Smaller Mag. Brightest = Negative Mag! Precision  Fractional Mag. Scale “Logarithmic” App. Mag.  Observer Position! (Distance)

The “Absolute Magnitude” Scale (vs. True Brightness (“Luminosity”)  = App. Mag. as seen from 10 parsecs away)

How to tell a Star’s Temperature from its Spectrum (w/Planck Curves)

A Star’s Spectral Lines actually depend upon Temperature, too! (indirectly…)

(Bigger stars always hotter…?) (Both K-type!)

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