Answer:
Doppler shift of the starlight
Explanation:
To predict the movement of a star, we compare the spectra of elements found in star (H, He Na etc.), first spectra which are obtained from star and second spectra from laboratory. If spectral lines of the spectra obtained from star, are shifting towards red end (called red shift) then star is going away from earth and if shifting is towards blue (called blue shift), then star is approaching the earth. This is Doppler's shift.
Answer:
Three types of electromagnetic waves, used to transmit various information
Explanation:
A form of energy waves having both electric & magnetic fields are Electromagnetic waves. Three types -
Radio Waves - These have longest wavelengths & transmit data through radio, satellites, radar .
Micro Waves - These have shorter wavelengths & are used in cooking appliances & predicting weather.
X rays - These have more short wavelength and can penerate soft tissues like skin & muscle, hence are used for medical examining
a . true hardness and density are physical properties