- Astronauts on the ISS have captured the illusion of our moon being ‘squashed’ in space
- A video from Nasa’s Terry Virts shows the effect that occurs when the moon begins to dip below the horizon
- When ISS passed this moonrise, the light from the top part of the moon was moving through less air than that at the bottom – which is being viewed through Earth’s atmosphere – causing the lower light to bend and ‘squash’ the moon
Jonathan O’Callaghan for MailOnline
08:36 EST, 7 January 2015
16:13 EST, 7 January 2015
The moment the sun dips below the horizon – a sunset – is a phenomena known to all on Earth, accompanied by fantastic colours and a transition from day to night.
But a lesser known phenomenon has been captured by astronauts on the ISS, showing the moment of a moonset – when our largest natural satellite dips below the horizon.
And remarkable ‘squashing’ effect, not always easily visible to observers on Earth, are also made apparent in the images.
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Astronauts on the ISS have captured a ‘squashed’ moon from space (shown). A video from Nasa’s Terry Virts from Maryland shows the effect in action. It occurs when the moon begins to dip below the horizon and the light must travel through the atmosphere and is refracted
The latest pictures were taken by Nasa astronauts Butch Wilmore and Terry Virts on the ISS.
In a Vine showing the moon setting, Mr Virts said: ‘Moonset behind Earth’s atmosphere appears to land on a soft pillow of clouds.’
WHY DOES THE MOON LOOK SQUASHED FROM THE ISS?
The moon’s appearance as a squashed orb is actually caused by refracting light, similar to the apparent bending of a pencil placed into a glass of water.
Light passing from the vacuum of space through the air of Earth’s atmosphere can get a bit bent, causing the effect.
Depending on how much of the atmosphere has to go through – or how low the moon is through the horizon – the more squashed it will appear.
This is because light from different parts of the moon reach the observer’s eye at different speeds, so it doesn’t look normal.
The amazing video shows the moon slowly passing down through Earth’s atmosphere as the ISS makes its way around our planet.
In the images an odd ‘squashing’ effect can be seen as the moon makes its way down.
When the ISS passed this moonrise, the light from the top part of the moon was moving through less air than that at the bottom – which is being viewed through Earth’s atmosphere – causing the lower light to bend.
According to astronomer Nick Howes, who works with the Kielder Observatory in the UK, this is due to an effect known as atmospherics.
‘Light passing through our atmosphere as seen from a vantage point on the ISS will be refracted; the amount of refraction is dependent on the airmass it passes through,’ he told MailOnline.
‘The moon being a relatively (as seen by the eye) large object across, the amount of refraction varies from top to bottom, causing the squashed effect.’
The moon also turns slightly red (seen here) because the amount of refraction causes only particular wavelengths of light to be visible, in this case red, a similar effect to sunrise and sunset
He said you could ‘very tentatively’ liken the effect to a star appearing bent if you look at it in a glass of water.
Astronomer Ninian Boyle also said the effect can actually be noticed from Earth in particular instances.
‘If you photograph moonrise and moonset, as I have done on many occasions, you’ll see the same effect – the moon looking like a slightly flattened orange,’ he said.
From the moon looking at Earth (picture from Apollo 8 in December 1978 shown), no such ‘squashing’ effect is visible because the moon has no atmosphere