Canstellation
- a region in the sky with well-defined borders of stars that form a recognisable pattern in the sky
We have 88 castellations
Celestial sphere
-an imaginary sphere in which objects in the sky appear to reside when observed from Earth
Local sky
A sky that is seen from a particular location,
Has the form of a dome,
Only half of the celestial sphere is seen
because of horizon
Precession
-a graduate wobbling of the Earth’s axis around a line perpendicular to the orbit
The circuit takes 26,000 years
=> the North Star changes over time as well as constellations (zodiacs) that we see in different points on the orbit
Ecliptic
The Sun’s apparent annual path around the celestial sphere
Local sky
Ecliptic
The Sun’s apparent annual path around the celestial shere
Canstellation
A regional in the sky with well-defined borders of stars form a recognisable pattern in the sky
Angular size
A measure of an angle formed by extending imaginary lines outwards from your eyes to span an object
Angular size of the Moon = angular size of the Sun = 1/2 (градусов по Цельсия)
Celestial sphere
An imaginary sphere in which objects in the sky appear to reside when observed from Earth
Angular distance
An angle that appears to separate two objects in the sky
(NB your fist is ~10 cm and your palm with opened fingers - ~20 cm)
Сircumpolar star
A star that is always remain above horizon at a certain altitude so it is always seen
The formula of the angular size
Angular size/ 360 (degrees) = physical size/ 2pi*distance
Latitude
Measures north-south position
Parallels
0 degrees at equator
Longitude
Measures the east-west position
Meridians
0 degrees at Prime meridian (goes through Greenwich, England)
Why night sky changes through out the year?
Because of Earth’s changing positions in its orbit around the Sun.
The annual orbit of Earth makes the Sun appear to move eastward along the ecliptic through out the year with different constellations in the background
(—> Zodiacs)
What causes seasons?
The Earth’s axis tilt — causes sunlight to fall differently on Earth at different times at year.
The Northen Hemisphere is tipped towards the Sun in summer and is tipped away from the Sun in winter; the reversed is true for the Southern Hemisphere.
Note that Spring and Fall begin when sunlight falls equally on both hemispheres
June solstice (= summer solstice)
A moment when the Northern Hemisphere is tipped most directly to the Sun and receives the most direct sunlight
June 21
December solstice (=winter solstice)
The moment when the Northern Hemisphere receives the least direct sunlight
Dec 21
March equinox (=spring equinox)
The moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped towards the Sun
March 21
September equinox (=fall equinox)
The moment when the Northern Hemisphere goes from being tipped slightly towards the Sun to being tipped away from the Sun
Sep 22
How long is the day? 2 types
1) 23hr 56 min — **sidereal day ** — how long it takes a star to make one full circuit through the sky (to get to the initial meridian)
2) 24hr — solar day — how long it takes the Sun to make one full circuit through the sky (to get to the initial meridian)
A sidereal day
How long it takes a star to make one full circuit through the sky
23hours 56 minutes
Why do we have leap years?
We have leap years in our modern calendars to keep solstices and equinoxes around the same dates
as they shift because of the precession (axis’s wobbling)
