The statement is incorrect. The observations of 21cm line is an useful probe for redshifts up to 150, while CMB (which is more correct to call "first light") is redshifted by ~1100 times.atomiclaser said:Summary:: 21 cm was considered as the first light after big bang. How does people measure this emission ?
we know that all emission from asctrophysical context is doppler shifted. So, how to make sure the doppler shifted 21 cm not contaminated by some other emission?
To measure a 21 cm EM wave that is Doppler shifted, you would need to use a radio telescope. This telescope is equipped with a receiver that can detect the 21 cm wavelength and measure its frequency. The frequency of the wave can then be compared to the expected frequency to determine the amount of Doppler shift.
The expected frequency of a 21 cm EM wave is approximately 1420 MHz. This is known as the "hydrogen line" and is used as a standard for measuring Doppler shifts in space.
Measuring a 21 cm EM wave can provide valuable information about the motion and distribution of hydrogen gas in space. This can help scientists study the structure and evolution of galaxies, as well as the dynamics of cosmic objects such as stars and planets.
Yes, the amount of Doppler shift in a 21 cm EM wave can be used to calculate the speed of an object. This is known as the Doppler effect and is commonly used in astronomy to measure the velocities of celestial objects.
Yes, there are other methods for measuring a 21 cm EM wave. For example, the wave can also be detected using a spectrometer, which measures the intensity of the wave at different frequencies. Additionally, spacecrafts can also be equipped with instruments to measure 21 cm waves in space.