A100 Solar System
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Transcript of A100 Solar System
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A100 Solar
System
Today’s APOD
Read Chapter 1 in text – History of Astronomy
Quiz Today (essential facts and scientific notation)
Rooftop Session Sept. 10, 9 PM 1st Homework due Friday (get it on Oncourse)
The Sun Today
Monday, Sept. 8
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First Quiz• Bubble and write your name on the
Scantron form• You may consult with your neighbors• No books, notes, papers, internet,
cell phones
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What can we see in the night sky?With the naked eye, we can see more than 2,000 stars, as well as 5 planets, the Moon, comets, meteors, the Milky Way, and a few other special objects The Milky Way is a band of light that makes a circle around the celestial sphere
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Orion rising
The night sky is familiar, but few people look closely at (or think about) the complex phenomenawe observe in sky.
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The Sky!
The brightness of a star is shown by the size of its dot
North
South
Jupiter & the Moon in Sagittarius
Sky chart for 9 PM TONIGHT
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Jupiter & the Moon in Sagittarius
Sept 9Sept 8
Just look south… Jupiter is the brightest object in the southern sky
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Check out the just south of west, just after sunset
• See Mercury, Venus, and Mars
• You will need to be able to see low on the horizon to the west southwest
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ConstellationsA constellation
is a region of the sky
Constellation regions are irregular in
shape
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Do the Stars in a constellation belong together?•NO!•The stars in a constellation are not all at the same distance from the Sun
•They do not form a real group in space
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The Big Dipper is part of the constellation
Ursa Major
The stars of the Big Dipper are not all at the same distance from the Sun
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The Constellations
The 88 official (defined by the International Astronomical Union) constellations cover the celestial sphere
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The Celestial Sphere
The stars all appear to lie on a large sphere surrounding the Earth (the celestial sphere)
Really, the stars are all at different distances
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Angular Measurement
s
• Full circle = 360º• 1º = 60 (arcminutes) • 1 = 60 (arcseconds)
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We measure the sky
using angles
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Measure the Angular Size
Image taken by the Galileo spacecraft (Jupiter, 1995-97) during its lunar fly-by in December, 1992
Tycho impact basin
The dark areas are lava rock filled impact basins (mare)
The “real” Moon is ½ degree across
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Angular Size distance 2
degrees 360 size physical = sizeangular
An object’s angular size appears smaller if it is farther away
The angular size of Mars changes depending on where Earth and Mars are
in their orbits
angular size
physical size
distance
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The Local
Sky
An object’s altitude (above horizon) and direction (along horizon) gives its location in your local sky
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Definitions:The Local Sky
Zenith: The point directly overhead
Horizon: All points 90° away from zenith
Meridian: Line passing through zenith and connecting N and S points on horizon
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Our view from Earth:• Stars near the north celestial
pole are circumpolar and never set.
• All other stars (and Sun, Moon, planets) rise in east and set in west.
Celestial equator
A circumpolar star never sets
This star never rises in Indiana
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Why do stars rise and set?
Stars in the northern sky circle the northern celestial pole (in the southern hemisphere stars circle the southern celestial pole)
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The Earth spins under
Polaris
(Polaris is NOTthe brighteststar in the sky!)
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Finding Polaris
Find the Big Dipper in the northwestern sky
Sky chart for 9 PM TONIGHT
Find an open area away from nearby lights where you have a good view of the sky
North
South
Big Dipper’s on its side in the northwestern
sky
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Finding Polaris
To find Polaris:• find the Big Dipper• follow to Polaris• the Big Dipper is ALWAYS up
in Indiana!
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Altitude of the celestial pole
= your latitude
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Why do the constellations we see depend on latitude and time of year?
They depend on latitude because your position on Earth determines which constellations remain below the horizon.
They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars.
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The sky changes as Earth orbits the Sun
As the Earth orbits the Sun, different constellations are visible at night
At midnight, the stars on our meridian are opposite the Sun in the sky
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Where on the Earth is it possible to see the most stars through the year?
a) From the north pole b) From latitude 23.5 degrees c) From the equator d) anywhere, since latitude makes
no difference.
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Precession!Over time, the
direction of the Earth’s rotation axis drifts around a circle.
At different times, different stars (other than Polaris) are close to the pole
The location of the celestial pole traces out a circle in the sky every 26,000 years
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Vocabulary ReviewoConstellationoEclipticoEquatoroCelestial
sphereoLatitudeoLongitude
oMeridianoZenithoHorizonoAltitudeoNorth and
south celestial poles
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One question I’ve always had about astronomy is…
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ASSIGNMENTSthis week
Read Chapter 1, History of…
Kirkwood Obs. open Weds. Rooftop Sky Viewing Weds. 1st HW due Friday
Dates to Remember