Midterm 1 Flashcards
Zenith
The point directly overhead (based on a persons location standing on the earth)
Altitude
The height of a star above the horizon
Solstice
The date in the Northern hemisphere when the Sun is as high in the sky as it gets (Summer solstice - June 21)
-also highest point above celestial equator
-lowest in winter sky is the winter solstice (Dec. 21)
Caused bc of the tip of the earth
Ecliptic
The path of the Sun through the sky over the course of a year
- moon and planets remain near this line
- bc of the 23 degree tip of the Earth’s axis, the Sun doesn’t follow the celestial equator
Meridian
A line form due north, through Zenith, to due South
-based on your location on earth (diff. depending where you are - whereas equator and poles are always the same)
Equinox
The point where the ecliptic crosses the celestial equator
- Vernal Equinox (Mar. 21)
- Autumnal Equinox (Sept. 21)
- represent beginning of spring and fall
Celestial Equator
The extension of the Earth’s equator onto the celestial sphere
Azimuth
An angle measured from due north (Around to the east) to a point along the horizon under a celestial objecy
Declination
An angular measure of the distance of a star north or south of the celestial equator
Diurnal motion
-the rotation of the Earth
-Causes the nightly motion of the stars
(rise in the East and set in the West)
Right ascension
A measurement of a stars position measured along the celestial equator starting at the Vernal Equinox. Measured in a unit of time
On a given night we see different stars at different times of the night. 6 months later we see a different set of stars during the night - why?
- Stars change on a given night due to the rotation of the earth on its axis
- after 6 months the stars change due to the orbit of the earth
The Old Testament talks about the north star..is it referring to Polaris?
This would not be reference to Polaris bc the earth wobbles in precession, causing the position of the stars to change in the night sky. (Changes slowly over 26,000 years) The position of the North Celestial Pole has changed over time and pointed to other stars besides Polaris.
Celestial sphere
N and S Celestial poles and Equator are extensions of Earth’s poles and Equator
Constellations
Latin ‘group of stars’
- used to define regions of the sky and to tell the seasons
- 88 constellations
Astronomy as navigation (2 systems)
Many observatories established to monitor the positions of stars so they could be used for navigation
- also used to establish local time and local start to the longitude system
- height of N star s important to navigation
2 systems to give positions of the stars
- Altitude/Azimuth
- Right ascension/declination
Altitude and Azimuth
Altitude - the height above the horizon
Azimuth - an angle measured from N around to the E
-in this system: measure to right below the star in azimuth and then measure up to get the altitude
(PROBLEM bc stars position changes as earth rotates)
Right ascension and declination
(Uses poles and equator)
Right Ascension
-longitude like measure
-measured about the Celestial Equator (in units of hour, min, sec
-0 point is at the vernal equinox - then measure around the equator to the east
Declination
- latitude like measure
- measure angle above or below the Celestial Equator
- measured in degrees, min, sec
- Celestial Poles are at 90 degrees N or S (+ or -)
“Precession of the Equinox”
Earth wobbles over time
- changes the direction of the pole and therefore the position of the equinox and the N star
- causes the celestial poles and equator to slowly change positions
Where is Universal Time for astronomy
Greenwich, England
-also the location of the Prime Meridian, or starting point of the system
Before time zones how was 12:00 pm defined in a given city?
The time when the Sun was due south (on the meridian)
How long does it take for the Earth to make one complete rotation on its axis
23 h 56 m of SOLAR time
For western world, what calendar do we use?
The Gregorian calendar
Took a trip to Anchorage, Alaska where latitude is 61.2 degrees N. Where would we expect to find Polaris in the sky?
Lower in the sky than in provo (40 degrees N)