The Celestial Sphere Flashcards
What does this mean
Right Ascension
(RA/α)
- Equivalent of longitude
- Angle of an object measured around the celestial equator
0 → 360◦
What does this mean
Declination
(Dec/δ)
- Equivalent of Latitude
- Angle of an object measured from celestial equator
-90◦ → +90◦
What does this mean
Azimuth
Angle of an object measured from North around the horizon
What does this mean
Celestial Sphere
Imaginary sphere carrying stars that spin around the observer
What does this mean
Ecliptic
Great circle path on celestial sphere that the sun follows
What does this mean
Meridian
Imaginary line in the sky over an observer from North to South
What does this mean
Sidereal Day
Time taken for Earth to rotate once, relative to the “fixed” stars
What does this mean
Solar day
Time taken for Earth to rotate once, relative to the Sun
RA and Dec of
Vernal Equinox
- RA = 0
- Dec = 0
- Hours of daylight = Hours of night
RA and Dec of
Summer Solstice
- RA = 90
- Dec = 23.5
- Longest day of the year
- Most northern point of Sun’s path
RA and Dec of
Autumn Equinox
- RA = 180
- Dec = 0
- Hours of daylight = Hours of night
RA and Dec of
Winter Solstice
- RA = 270
- Dec = -23.5
- Shortest day of the year
- Most southern point of Sun’s path
Declination of Ecliptic
(Sun’s Path)
23.5
The offset from the equator to the ecliptic
How to find the max altitude of an object in the sky
δ > ϕ
90◦ + ϕ − δ
Declination = δ. Latitude = ϕ
How to find the max altitude of an object in the sky
δ < ϕ
90◦ + δ − ϕ
Declination = δ. Latitude = ϕ
