Download Early history of astronomy

Lecture 3:
The Sun
&
Constellations
Professor Kenny L. Tapp
Early history of astronomy
Birth of modern astronomy
• Noted scientist
• Johannes Kepler (1571-1630)
• Ushered in new astronomy
• Planets revolve around the Sun
• Laws of planetary motion
• Orbits of the planets are elliptical
• Planets revolve around the Sun at varying speed
Positions in the sky
Early history of astronomy
Birth of modern astronomy
• Noted scientist
• Galileo Galilei (1564-1642)
• Supported Copernican theory
• Used experimental data
• Constructed an astronomical telescope in 1609
• Four large moons of Jupiter
• Planets appeared as disks
• Phases of Venus
• Features on the Moon
• Sunspots
Astronomical coordinate system on
the Celestial Sphere
Stars appear to be fixed on a spherical shell
(the celestial sphere) that surrounds Earth
Equatorial system of location
• A coordinate system that divides the celestial
sphere
• Similar to the latitude-longitude system that is
used on Earth's surface
• Two locational components
• Declination – the angular distance north or south of the
celestial equator
• Right Ascension – the angular distance measured eastward
along the celestial equator from the position of the vernal
equinox
Figure 21.16
Earth motions
Two primary motions
The difference between a solar
day and a sidereal day
• Rotation
• Turning, or spinning, of a body on its axis
• Two measurements for rotation
• Mean solar day – the time interval from one
noon to the next, about 24 hours
• Sidereal day – the time it takes for Earth to
make one complete rotation (360º) with
respect to a star other than the Sun – 23
hours, 56 minutes, 4 seconds
Figure 21.19
Earth motions
Gradual change in size of Sun
Two primary motions
• Revolution
• The motion of a body, such as a planet or moon, along a
path around some point in space
• Earth's orbit is elliptical
• Earth is closest to the Sun (perihelion) in January
• Earth is farthest from the Sun (aphelion) in July
• The plane of the ecliptic is an imaginary plane that
connects Earth's orbit with the celestial sphere
Now 40% brighter, 6% larger, 5% hotter
Solar Prominence
Solar Flares
Astronomy Picture of the Day
Solar Wind
NASA.gov
Auroras are caused by the
solar wind.
http://sohowww.nascom.nasa.gov/
Auroras on Saturn
The Constellations
Circumpolar Constellations
– Star patterns named by
ancient peoples after gods,
goddesses, animals,
monsters, and mythic
heroes.
– The constellations used by
Western Culture today
originated in Mesopotamia
around 3,000 B.C.
– Today 88 constellations are
recognized
– The brightest stars in a
constellation are identified
in order of their brightness
by the letters of the Greek
alphabet – alpha, beta, and
so on
• Always above the horizon (though often
very low)
• Everything with declination higher than
90º minus your latitude (90 - 35 = 55ºN
for us)
• For us: Ursa Minor, Ursa Major,
Cassiopeia, Cepheus, & Draco
Polaris: The North Star
21"March"2007
10:00"PM
The"Spring"Sky
•"Barely moves with time of day
or season
• Its altitude = your geographic
latitude
• A double star
• A cepheid variable star"""
•"How"to"Find"it:""
From the Dipper, follow the
two stars at the end of its bowl
toward Cassiopeia. There,
about five times the separation
of these two stars, you'll find
Polaris.
Use the middle three stars of
Cassiopeia's "W" as an arrow to
point in the direction of the
Dipper. Halfway there you will
encounter Polaris.
(Oklahoma City, OK)
Polaris
Polaris
(North Star)
(North Star)
(Oklahoma City, OK)
Big Dipper
Venus
Orion
constellation
(winter only)
www.skymania.com
http://lcogt.net/virtualsky
Cassiopeia
Ursa Minor
Big Dipper/Ursa Major
This Month’s Sky Map
Download from Course Website --> Next Time