Transcript Chapter 2 - Backyard Astronomy

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Learn to use a star chart like one at end of text
Know where north is. Use compass or GPS.
Match star chart to the night sky
Find the brightest stars first
Big Dipper is easiest to find
– Asterism – star group that is part of constellation
– Part of constellation Ursa Major (Great Bear)
• Determine angles
with hand held at
arm’s length
– Fully spread hand
is 20 degrees
– Width of thumb is
2 degrees
– Width of little
finger is 1 degree
• Describe location of star by clock position
• Example: Star is 2 hands from the moon at
the 4 o’clock position
• Summer Triangle
– Asterism that spans three different constellations
– Cygnus, the Swan
– Aquila, the Eagle
– Lyra, the Harp
– Consists of 3 bright stars: Deneb, Altair, and Vega
• Big Dipper can be used to find other asterims
and stars
• If you extend the arc of the handle, you go to
Arcturus (follow the arc to Arcturus)
• Pointer stars at front of Big Dipper point to the
North Star, Polaris.
• Polaris is the end of the handle of the Little
Dipper (asterism of Ursa Minor or Little Bear)
• Polaris is the North Star because it lies almost
exactly above the Earth’s North Pole.
• It is only star that shows no apparent motion
during the night.
• Other stars seem to rotate around it
• Other constellations near the Little Dipper are:
– Cepheus, the king – looks like a house
– Cassiopeia, the queen – looks like a large W
• The middle part of the W points to the North Star.
– Andromeda, the princess
– Pegasus, the winged white horse
– Perseus, the hero
– Cetus, the sea monster
• Greek mythology has stories about the stars
• Orion, the Hunter
– Canis Major and Canis Minor
– Taurus, the Bull
– Lepus, the Rabbit
– Pleiades, the maiden sisters
– Scorpius, the Scorpion
Photography
• Mount camera on tripod
• Set lens aperture as wide open as possible
to allow as much light to enter as possible
• Set the ISO setting to maximum
• Typical exposure time is 10 seconds
• 15 seconds or more you will see star trails
• Celestial Coordinates
• Right Ascension (RA) similar to longitude
– Divides celestial sphere into 24 hour zones
– Each hour would be equivalent to 15 degrees
– 0 h 0 m 0 s of RA is where the Sun’s path (ecliptic)
crosses the celestial equator as the Sun moves north
• Declination (dec) similar to latitude
– +90 degrees is north celestial pole
– -90 degrees is south celestial pole
– 0 degrees is celestial equator
• Can also locate stars with altitude and azimuth
• Altitude – angle above the horizon
• Azimuth – angle eastward along horizon from North to the
point directly below the object.
• Problem: altitude and azimuth of star constantly changes as
it moves across the sky. (RA and dec is better)
Star Chart
• Map of the stars
• M32 is a galaxy in the Local Group
– RA is 0 hours, 42.7 minutes
– Dec is +41o 16’
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Black circles are stars
Size of star indicates brightness
Red ellipses are galaxies
Blue shading shows brightness of Milky Way
Planetary Configurations
• Conjunction – planet lies in same direction as the
sun
– Inferior conjunction – planet is between earth and sun
– Superior conjunction – planet is on other side of sun
• Opposition – planet is directly opposite the sun
• Transit – planet passes between earth and the
sun
– Like a solar eclipse
– Only Mercury and Venus can transit the sun as
seen from earth
• Venus will transit the sun this summer!
– June 5 starting at 5 PM
• Venus
– Morning Star – seen in the morning
– Evening Star – seen in the evening
• Dark Adaptation – eyes will become more
sensitive the longer you stay in dim light
– Will be able to see more stars!
– Pupil opens wider
– Takes 20 minutes, but undone if exposed to bright
light!
– Color sensitivity is lower
• Averted vision – greater sensitivity to faint
objects if you look to the side