Basic terms and concepts. Measuring distances Astronomical unit (AU) is defined as the distance...
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Transcript of Basic terms and concepts. Measuring distances Astronomical unit (AU) is defined as the distance...
ASTRONOMYBasic terms and concepts
Measuring distances
Astronomical unit (AU) is defined as the distance from the Earth to the Sun.
1 AU is about 150 million kilometers We measure the distances in our Solar
System using the Astronomical Unit For example: Mercury is 0.3 AU from the
SunNeptune is about 30 AU from the Sun
Measuring Distances
Beyond the Solar System the AU is not very useful, use light year.
One Lightyear is the distance that light travels in one Earth year.
1 ly = 300,000 km/s x 365.25 days/yr x 24 hr/day x 60 min/hr x 60 sec/min = 1013 km
We are a few light years from the nearest star
Celestial Sphere
Celestial Sphere
The Celestial Sphere is an imaginary dome on which all the stars are projected.
It appears like all the stars are at the same distance from Earth.
On Earth it is like a dome, the ground blocks the lower part of the sphere
From out in space, it would appear like a sphere with the Earth at the center.
Celestial Sphere
Celestial Sphere
The Celestial Sphere is a model that helps us to simplify the location and motion of the celestial bodies.
We can put a grid on the Celestial Sphere, much the same as lines on a globe. These can be used to locate stars and constellations
Coordinates of Celestial Sphere
Declination and Right Ascension
Lines of Declination are the lines that run East West (pink)
Use “dec” to indicate the declinationValues are from +90 degrees to -90 degrees
The lines of Right Ascension “RA” are the lines that run from pole to poleDivided into 24 segments (each segment is
called an hour)Coordinated given in hours, minutes,
seconds.
Declination and Right Ascension
The point 0h, 0m, 0s is where the Sun’s path crosses the celestial equator.
The Celestial equator is the 0 degree of declination
The path of the Sun across the CS is known as the Elliptic
Elliptic
Elliptic
The belt shaped region surrounding the Elliptic passes through the twelve constellations of the Zodiak
Zodiak means little animals The position of the sun at any time of
the year is related to the constellation of the Zodiak.