Astronomy: Chapter 2
Greeks: could not detect what?
Stellar parallax.
Our galaxy: shaped like what?
- A disk
What eclipse occurs at a new moon?
Solar eclipse.
When is summer?
Solstice which occurs June 21st.
Solar eclipse: within umbra? Within penumbra?
Total solar eclipse. Partial solar eclipse.
The Earth's axis is tilted _____ from being perpendicular to the ecliptic plane.
23.5 degrees.
The celestial equator is tilted ______ to the ecliptic.
23.5 degrees.
How long is the cycle of lunar phases?
30 days.
The sun spends how long North of the celestial equator? How long south?
6 months, 6 months.
1 degree= ?
60 arcmin
1 arcmin= ?
60 arcsec
How many constellations in the sky?
88
Horizon: definition?
All points 90 degrees from the zenith.
Celestial Sphere: definition?
An imaginary sphere surrounding the Earth upon which the stars, Sun, Moon, and planets appear to reside.
Most official constellation names come from ______.
Antiquity
Ecliptic: definition?
Apparent path of the sun from the sky.
Parallax Angle: definition?
Apparent shift of a star's position due to the Earth's orbiting of the sun.
Right Ascension: definition?
Distance east of vernal equinox (where the sun crosses the celestial equator going North).
Meridian: cycle? (3)
Due North Horizon-> Zenith-> Due South Horizon.
Seasons: caused by what?
Earth's axis tilt.
The ______ is the same as the Earth's axis precesses.
Earth's tilt.
As the Earth orbits the Sun, the Sun appears to move...
Eastward with respect to the stars.
Lunar eclipse: who can see it?
Everyone on the nighttime side of Earth.
If you are standing at the equator, what happens?
Everything rises & sets 90 degrees to the horizon.
Stars were ________ ____ then the Greeks thought.
Farther away.
Phases of the moon: waning
Full, gibbous, last quarter, crescent.
How do we measure the sky?
In angles, not distances.
What eclipse occurs at a full moon?
Lunar eclipse.
Solar Eclipse: must be within what to see it?
Moon's shadow.
Phases of the moon: waxing
New, Crescent, First Quarter, Gibbous
The sky appears to rotate around the...
North or South celestial poles.
If you are standing at the poles, what happens?
Nothing rises or sets.
The Sun: circles the celestial sphere how often?
Once every year.
Rotation period= ? Reason why....
Orbital period. We see the same side on our moon.
Our galaxy: contains what?
Our solar system
The patterns of stars have no _________ ________.
Physical Significance.
Retrograde motion: definition?
Planets usually appear to move Eastward relative to the stars, but sometimes move west for a few weeks or months.
_______ won't always be the North Star.
Polaris.
Longitude: definition?
Position east or west of Prime Meridian.
Declination: definition?
Position north or south of the celestial equator.
Latititude: definition?
Position north or south of the equator.
The Earth's axis _______ once every ________ years.
Precesses 26,000.
Constellation: definition?
Region of the sky.
Altitude: definition?
The angle above the horizon.
Ecliptic: definition?
The annual path of the Sun through the celestial sphere, which is a projection of ecliptic plane.
Zodiac: definition?
The constellations which lie along the ecliptic.
Celestial Equator: definition?
The extension of the Earth's equator onto the celestial sphere.
Our galaxy: named what?
The milky way galaxy.
Zenith: definition?
The point directly above you.
North and South Celestial Poles: definition?
The points in the sky directly above the Earth's North and South poles.
Precession changes what? (2)
The position in the sky of the celestial poles, and the equinoxes.
Why was the Parallax angle difficult to explain for the Greeks? (2)
They believed Earth was at the center of the universe. Too far away for the naked eye to notice.
Eclipses: definition?
When the earth and the moon pass through each other's shadows.
Equinox: definition?
Where the ecliptic (sun) intercepts the celestial equator.
Solstice: definition?
Where the the ecliptic (sun) is farthest from the celestial equator.
We see moon phases because...
half the moon illuminated by the sun and half dark.
As the Earth rotates, the sky appears to...
rotate in the opposite direction.
We see some combination of...
the light and dark faces.