Honors Astronomy: chapter 1

Published by admin on

Constellations
Stars that are in some sort of pattern that the human brain has created/ large regions in the sky that include many original star patterns as well as surrounding stars
Asterism
Another name for a recognizable pattern in a group of stars
-Navigational aid
-time keeping
-story telling
Important functions of constellations
Celestial sphere
An imaginary sphere around Earth that can use two dimensional spherical coordinates (similar to longitude and latitude) to locate sky objects
Celestial equator
Projecting the Earth’s equator onto the celestial sphere forms this
Celestial poles
The locations where Earth’s axis intersects the celestial sphere
Declination
Degrees north or south of celestial equator (similar to latitude)
Right Ascension
Measured in hours, minutes, and seconds eastward from position of the sun at vernal equinox (similar to longitude)/ ranges from positive 90 degrees to negative 90 degrees
Diurnal motion
Daily progress of sun and other stars across the sky caused by the Earth’s rotation on its axis
Solar day
The 24 hour period from one noon to the next day and is our basic social time unit.
Sidereal day
A day measured by the location of the stars (23 hours 56 minutes)
Stars
What shifts about 1 degree each day?
Ecliptic
The path that makes the sun appear to move appear to move relative to the background stars
Zodiac
The 12 constellations the sun passes through on its ecliptic path
23.5 degrees
How many degrees off is the ecliptic path from the celestial equator?
Northernmost point
Above the celestial equator; summer solstice
Southernmost point
Below the celestial equator; winter solstice
Vernal and autumnal equinoxes
Points where path crosses the celestial equator
Earth’s tilted axis
What causes the length of day and height of the sun to change throughout the year?
Tropical year
Time from one vernal equinox to the next
Precession
Rotation of Earth’s axis itself; makes one complete circle in about 26,000 years
Tropical year
What year follows the seasons?
Sidereal year
What year follows constellations?
Meridian
An imaginary line on the celestial sphere through the north and south poles, passing directly overhead at the given location
Mean solar day
The average of all solar days over an entire year
Time zone
Everyone adopted the mean solar time corresponding to a specific meridian inside the zone
Universal time
The mean solar time at Greenwich meridian
Leap year
The calendar would include one extra day every 4th year
Phases
The regular cycles of he changes of the moons appearance
29.5 days
How long does the lunar phase cycle take?
Sidereal month
(27.3 days) the moon completes one revolution and returns to its starting point on the celestial sphere
Synodic month
(29.5 days) it is longer than a sidereal month because of earth’s motion around the sun, the moon must complete slightly more than one full revolution to return to the same place
Eclipse
The sun and moon line up precisely with Earth
Lunar eclipse
Earth’s shadow sweeps across the moon, temporarily blocking the Suns light
Solar eclipse
The moon passes directly in front of the sun
Partial lunar eclipse
The alignment of the sun, earth, and moon is imperfect
Total lunar eclipse
The alignment of the sun, earth, and moon is perfect
Umbra
The central region of the shadow
Penumbra
The outer region of a shadow
Annular eclipse
The umbra never reaches the Earth at all
Eclipse seasons
When the line of nodes isn’t directly towards the sun or if the line of nodes briefly lies along the Earth
Apogee
When the moon is farthest away from Earth
Perigee
When the moon is closest to Earth
Categories: Astronomy