The month of July is set to witness a rare astronomical spectacle as a blood moon, the second of the year, will appear on the intermediary night of July 27-28.

The ‘Marathon’ Eclipse:

According to space experts, the eclipse will last one hour and 43 minutes – nearly 40 minutes longer than the January 31 Super Blue Blood Moon.

Why will the moon turn red?

• The blood moon, or the ‘full buck moon’ as it is being called, will turn blood red during the eclipse due to the way light bends around Earth’s atmosphere.
• During a blood moon, the moon takes on a deep red to orange colour, rather than completely disappearing when it passes through the shadow cast by Earth.
• This bizarre effect known as ‘Rayleigh scattering’ filters out bands of green and violet light in the atmosphere during an eclipse.

Why will this lunar eclipse be longer?

• The full buck moon will last longer than normal as it will pass almost directly through Earth’s shadow during the eclipse.
• At the same time, it will be at the maximum distant point from earth. Therefore, it will take longer to cross Earth’s shadow.

Rayleigh scattering:

The dispersion of electromagnetic Radiation by particles that have a radius less than approximately 1/10 the wavelength of the radiation. The angle through which sunlight in the atmosphere is scattered by molecules of the constituent gases varies inversely as the fourth power of the wavelength; hence, blue light, which is at the short wavelength end of the visible spectrum, will be scattered much more strongly than will the long wavelength red light.