Transcript Power Point Presentation

In the Night Sky
University of Scouting
March 24, 2012
Gary G. Smith
Table of Contents
•
•
•
•
•
•
•
•
Observing tools
Find the North Star
Earth Motions: Seasonal Constellations
Rotation: Clock
Magnitudes
Big Dipper as Pointer
Earth Orbit
Star Colors
(3)
(4)
(8, 11)
(9, 10)
(12)
(13-17)
(18)
(7)
Observing tools
• Your eyes with a dark sky
– Civil twilight: sunset + 30 minutes
– Nautical twilight: sunset + 60 minutes
– Astronomical twilight: sunset + 90 minutes
• Star maps with constellations and bright
stars marked, red flashlight
• Binoculars
• Telescope
How to Find the North Star
• This method only works in the Northern
Hemisphere
• Find the Big Dipper
• From the pointer stars draw a straight line
away from the open side of the dipper
• The first “bright” star on this line is the
North Star, also called Polaris
North Star Points of Interest
• Not the brightest star in the night sky.
• The altitude (in degrees) of the North Star
above the horizon is the same number of
degrees as your latitude north of the
equator.
• The North Star shows you true north, not
the magnetic north shown by a compass.
ToC
Earth Motions
• Rotation: Earth spins on its axis to give us day
and night (one day).
• Revolution: Earth revolves around the sun to
give us seasons of the year and different visible
constellations (~365 days).
• Wobble: just as a top wobbles about its spin
axis, so does the earth (~25,000 years).
• Sun: pulls the solar system around the center of
the galaxy (~200 million years).
Rotation
• Sun appears to rise in the east and
appears to set in the west.
• Stars appear to rise in the east and appear
to set in the west unless they are close to
the north (celestial) pole.
• Circumpolar stars appear to rotate around
the north star during the night hours (you
have a clock).
Star Magnitudes
• On a clear, dark night, the best human
eyes can see stars from 1st magnitude (the
brightest) down to 6th magnitude (very
faint). Each magnitude ~ 2.5 times brighter
than next.
• Beyond 6th magnitude, one needs
binoculars and telescopes to see faint
objects
Star Bright
• Two values determine just how bright a
star appears in our night sky:
• 1) how much light (energy) the star emits
• 2) how far away from earth the star is
• Think of this analogy: a candle and
spotlight held at different distances so they
look the same brightness to an observer.
Twenty Brightest Stars and
…Polaris
Data courtesy of Wikipedia
Stars as a Clock
•
Star Clock
Big Dipper as Pointer
Earth’s Orbit
•
Earth Orbit
Courtesy of the Office of Naval Research
Spring Constellations
"Courtesy of Windows to the
Universe,
http://www.windows.ucar.edu"
Summer Constellations
"Courtesy of Windows to the
Universe,
http://www.windows.ucar.edu"
Fall Constellations
"Courtesy of Windows to the
Universe,
http://www.windows.ucar.edu"
Winter Constellations
"Courtesy of Windows to the
Universe,
http://www.windows.ucar.edu"
ToC
Star Colors
• Stars come in different colors from red to
blue-white.
• The different colors indicate the surface
temperatures of the stars.
• Red stars have a “cool” surface, e.g. 3000
degrees.
• Blue-white stars have a “hot” surface, e.g.
12000 degrees.
Pointers to Winter Constellations
Pointers to Fall Constellations
Summer Pointers
ToC
Some Internet Sites
•
•
•
•
http://hubblesite.org/newscenter/
http://www.skyandtelescope.com/
http://www.spaceweather.com/
http://hubblesite.org/explore_astronomy/tonights
_sky/index.php
• http://www.slooh.com/#io2
• http://www.astronomy.com/asy/default.aspx
• Google Earth has Sky and Mars options