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panda.unm.edu/courses/sanfratello/SP09/astro101.html
Remember - Read syllabus and schedule (contains links to lecture notes, textbook reading assignments and suggested problems from the text.)
What properties of physical objects would you expect to be important in Astronomy?
What properties of physical objects would you expect to be important in
Astronomy? Mass Size Distance from Earth Temperature Speed and Velocity Brightness (Luminosity) Age Chemical composition
Properties of Matter
Mass (How much “stuff” there is)
1 kilogram (kg) = 1000 grams (g) = 2.2 lbs
We tend to use mass and weight interchangeably, but weight depends on gravity.
“Massive”
Difference between Mass and Weight:
Mass of cat on Earth = Mass of cat on Moon
BUT,
Weight of cat on Earth = 18lbs
Weight of cat on Moon = 18/6 lbs = 3lbs
Distance
1 meter (m) = 100 centimeters (cm) = 39.4 inches (slightly longer than a yard)
A way to measure the distance to far astronomical objects is using ANGULAR measures – parallax
Volume (How much space something takes up)
1 cm3 = 0.06 cubic inches(about the size of a sugar cube)
2 cm1 cm
2 cm
2 cm x 1cm x 2 cm = 4 cm3
Density (How much stuff is concentrated in an object)
Density = Mass (g / cm3) Volume
Densities of Common Substances
Balsa Wood 0.13 g / cm3
Gasoline 0.7Water 1.0Polystyrene 1.05Average Rock 2.4Glass 2.6Ceramic 4.6Iron 7.9Lead 11.3Gold 19.3
Temperature (How hot something is)
The Kelvin Scale:
T(K) = T(oC) + 273 oC
"Absolute zero" 0 K = -273 oC
At what temperature (in Kelvin) does water freeze? Boil?
Speed and Velocity
Speed – how fast something is moving
Velocity – speed + direction = a vector quantity - an object can have the same speed but by changing its direction have a different velocity.
Angular Measures
90o
20o
360o, or 360 degrees, or 360 "arc degrees" in a circle.
1o = 60' or arcminutes1' = 60" or arcseconds
Angular Measure
Scientific Notation
(A shorthand way of writing large numbers, which occur often in astronomy).
We use powers, or exponents, of 10:
100 = 102 (= 10 x 10) 1000 = 103 (= 10 x 10 x 10)1,000,000 = 106 10 = 101 1 = 100 0.1 = 10 -1 0.0001 = 10 -4 0.007 = 7 x 10 -3
4000 x 0.002 = (4 x 103) x (2 x 10 -3)= 8 x 100 = 8
Add the exponents
Powers of Ten Video
Question
Why is looking at a distant astronomical object like looking into its past?
Scale of the Universe
• Speed of light– 186,000 miles/sec– 300,000 km/sec
• Light-year (LY)– Distance light travels
in one year• ~ 63,200 AU• ~ 6 trillion miles!
The Constellations
Northern constellations named for figures in Greek myth
Attempt to understand heavens
Astronomical Landmarks
Are the stars in a constellation all at about the same distance from the Earth?
The Constellation Orion
The Celestial Sphere
An ancient concept, as if all objects at same distance.
But to find things on sky, don't need to know distance, so still useful today.
The "Solar Day" and the "Sidereal Day"
Solar Day
How long it takes for the Sun to return to the same position in the sky (24 hours).
Sidereal Day
How long it takes for the Earth to rotate 360o on its axis.
These are not the same! Which is longer? Why?
(Demo)
One solar day later, the Earth has rotated slightly more than 360o .A solar day is longer than a sidereal day by 3.9 minutes(24 hours vs. 23 hours 56 minutes 4.091 seconds).
Difference due to rotation and revolution of Earth!
What causes the seasons?
Seasons
Summer Winter
In winter, sunlight is spread out more thinly across the ground => each bit of ground receives less radiation => cooler
Seasons caused by tilt of Earth’s axis of rotation.
Earth is farthest from sun during summer!
Precession
What causes precession? How long does one cycle take?
Precession
The Earth has a bulge. The Moon "pulls down" on the side of the bulge closest to it, causing the Earth to wobble on its axis.
Earth
Moon
Spin axis
**Vega Polaris
Precession Period 26,000 years!
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