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Astro. 2-2
The Sky and It's Motions
| Question | Answer |
|---|---|
| What is the celestial sphere? | The celestial sphere is a scientific model where the sky is thought of as a great sphere around us with the stars stuck inside like thumbtacks in a ceiling. |
| What is a "scientific model"? | A scientific model is a carefully devised mental conception of how something works, a framework that helps scientists think about some aspect of nature. It does not have to be true to be helpful. |
| What movement causes day and night on Earth? | Day and night are caused by Earth's Eastward rotation. |
| Because of Earth's Eastward rotation, everything in the sky appears to move in which direction? | Everything in Earth's sky appears to move Westward. |
| How do astronomers measure distances across the sky? | Astronomers measure distances across the sky as angle expressed in units of degrees and subdivisions of degrees called arc minutes and arc seconds. |
| Does where you are on Earth determine what you can see of the sky? | Yes, what you can see of the sky depends on where you are on Earth. Australia can never see the Big Dipper. |
| What is precession? | Precession is the 23.5 degree tilt of the Earth. (Hint: think of Earth as a top) |
| What causes precession? | Precession is caused by a slight bulge around the middle of Earth and the sun and moons gravitational pulls. |
| How often does Earth's precession make a complete circle? | Earth's precession completes a full circle every 26,000 years. |
| What is the "zenith"? | The "zenith" is the top of the sky above your head. |
| What is the "nadir"? | The "nadir" is the bottom of the sky directly under your feet. |
| What are the pivot points of Earth's rotation? | The pivot points of Earth's rotation are the north celestial pole and the south celestial pole located directly above Earth's north and south poles. |
| What is the "celestial equator"? | The "celestial equator" circles the Earth halfway between the celestial poles. |
| What are the "east point" and the "west point"? | The east point and west point touch the celestial equator halfway between the north and south points. |
| Does Polaris move? | Polaris (the North Star) hardly moves as the sky appears to rotate westward around it. |
| What is a "minute of arc"? | A "minute of arc" is 1/60th of a degree. |
| What is a "second of arc"? | A "second of arc" is 1/60th of a minute of arc. |
| How many degrees in diameter are the sun and the moon? | The sun and moon are each about 1/2 a degree in diameter. |
| What are "circumpolar constellations"? | "Circumpolar constellations" are constellations that never rise or set. |
| Do the celestial poles and the celestial equator change? | The celestial poles and the celestial equator are slowly changing thanks to Earth's precession. |
Created by:
rebecca_forcier
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