Total lunar eclipse on July 28: Here's all you need to know

SINGAPORE - Astronomy enthusiasts will have the chance to catch the longest total lunar eclipse of the century in Singapore on Saturday (July 28). Starting at 3.30am, the eclipse will last 1hr 43min.

The lunar eclipse will also coincide with the Mars opposition, where the planet is on the side of the Earth opposite to the Sun.

Mars will be near its closest approach to Earth since 2003. The red planet will thus appear as a bright reddish "star" close to the Moon throughout the night.

Here is everything you need to know about this cosmic event:

1. WHAT IS A LUNAR ECLIPSE?

Simply put, a lunar eclipse occurs when the Moon passes directly behind the Earth, and is thus shrouded by its shadow.

A lunar eclipse happens only during a full moon. The Sun and Moon need to be fairly exactly aligned, with the Earth in between them, for the event to happen.

A total lunar eclipse, as the name suggests, is when sunlight is completely blocked by the Earth from reaching the Moon.

The moon is 37 per cent obscured by the Earth's shadow during the partial lunar eclipse above Sydney on June 4, 2012. PHOTO: AFP

A solar eclipse happens when the Moon is between the Sun and the Earth, and the Moon partially or fully blocks the Sun.

A lunar eclipse can be seen from anywhere on the night side of the Earth, whereas solar eclipses can be viewed from only a small number of locations on Earth.

2. PHASES OF THE ECLIPSE

The total lunar eclipse will first start with the penumbral eclipse, where the diffuse outer shadow of the Earth will fall on the Moon. From Earth, this will appear as a dark shading on the Moon's face.

The next stage is the partial lunar eclipse, where the Earth's umbra, or shadow, takes a bite out of the face of the Moon. The Moon starts to take on a reddish tint as this "bite" grows larger.

Finally, we reach the "totality" - the period of time during the eclipse where all the light is blocked. The Moon now will appear completely red and this is when the Moon is closest to the centre of the Earth's shadow.

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3. THE MANY MOONS

Red or blood moon

The Moon appears a coppery red during lunar eclipses due to a simple phenomenon of optics: refraction.

Due to the eclipse, the only light reflected from the surface of the Moon is refracted by the Earth's atmosphere.

Particles in the atmosphere are smaller than the wavelengths of sunlight, which is made up of different colours.

Colours in the light that have shorter wavelengths (for example, blue), are scattered more strongly, and so are removed before the light hits the surface of the Moon during the eclipse.

Those with long wavelengths - red and orange - pass through and get refracted.

This effect is known as Rayleigh scattering, the same reason why the sky is blue or sunsets are red.

During a total lunar eclipse, the Moon can become a particularly deep, coppery red, and calling it "blood moon" probably arose out of a desire to make the event more dramatic.

Blue moon

A blue moon can refer to either the second full moon in a month that has two full moons, or the third full moon in an astronomical season of four full moons.

A moon that actually looks blue is - as the cliche suggests - very rare.

Only particles of a certain size in the air slightly wider than 900 nanometres can cause red light to scatter, making the moon seem blue.

This sometimes happens after forest fires or volcanic eruptions. For instance, reports of blue-coloured moon sightings followed the eruptions of Mount St Helens in the United States in 1980 and Mount Pinatubo in the Philippines in 1991.

Black moon

A black moon can refer to the second new moon in a month, where the moon is completely invisible. They occur once about every 32 months.

Another definition refers to the case where no new moons appear for an entire month, a situation only possible in February.

As February has 28 days and lunar cycles are 29.5 days, the month can sometimes miss either a full or new moon.

Supermoon

This refers to when a full moon coincides with the Moon being the closest to Earth. This point is also known as the perigee.

While there is no strict definition, this distance can be roughly less than 360,000km from the centre of the Earth.

The average distance between the Earth and the Moon is 382,500km.

Micromoon

A micromoon is so named because it looks smaller and less bright, appearing about 14 per cent smaller than normal.

This happens when a full or new moon coincides with the point in the Moon's orbit that is farthest away from the Earth.

This point is also known as the apogee, and can be anything farther than 405,000km from the centre of the Earth.

Mr Albert Ho, president of The Astronomical Society of Singapore, said that the Moon will be at apogee during Saturday's eclipse. The apparent size of the Moon will be smaller.

4. VIEWING THE ECLIPSE

Lunar eclipses can be safely viewed by the naked eye, said Mr Ho. This is unlike solar eclipses, which can permanently damage the eyes if viewed without safety equipment.

"As the moon is very bright and not affected by light pollution, any spot that provides you a clear unobstructed view of the sky from overhead to the western horizon will be suitable," he added.

Mr Ho recommended a pair of binoculars or telescope to enhance viewing pleasure.

Events

The Singapore Science Centre and the Lifelong Learning Institute (LLI) are also jointly organising a camp for families with children aged between seven and 12, starting at 6pm on Friday and ending at 7am the next day.

Apart from a viewing of the lunar eclipse, the Night With The Stars At LLI overnight camp includes a talk on the eclipse, workshops for both adults and children, and a family telescope-making session.

Unfortunately, the event is fully subscribed. Those interested can still write in to be placed on the waiting list. More details of the camp can be found here.

The Astronomical Society of Singapore will also be giving a talk on eclipses at the Science Centre Singapore observatory classroom on Friday at 8pm.

The talk is open to the public and will provide information about eclipses and how to view them, and discuss upcoming eclipses visible from Singapore.

Interest group Singapore Sidewalk Astronomy is also organising a stargazing activity from Friday night to Saturday morning. This starts at 10pm outside the McDonald's outlet in Bishan-Ang Mo Kio Park.

In a Facebook post on Saturday, the group said that surface features of Mars may not be as obvious through a telescope due to recent dust storms on the planet.

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5. WHERE IN THE WORLD?

Much of Europe, Asia, Australia, Africa and South America will be able to see at least some part of the eclipse happening on Saturday (it will still be Friday for some regions due to time differences).

Some of the cities include: Tokyo, Brussels, Lisbon, London, Budapest, Cairo, Egypt, Jakarta, Athens, Rome, Sydney, Singapore, New Delhi, Paris, Moscow, Beijing and Rio de Janeiro.

Singapore is relatively lucky, as the total lunar eclipse can be viewed in its entirety from here.

But we will not be able to see the penumbral eclipse that signals the end of the event, as the moon would be below the horizon for Singapore at that time.

People living in India, Pakistan, Saudi Arabia, South Africa and other nearby countries will be able to see everything, while most of North America will not be able to see the eclipse at all.

6. LUNAR EVENTS, PAST AND FUTURE

On Jan 31 this year, a lunar eclipse, blue moon and a super moon occurred simultaneously. During the event, the total lunar eclipse lasted 1hr 16min.

Around 5,000 visitors flocked to The Observatory at The Science Centre Singapore to use telescopes at a special viewing session.

The cosmic coincidence last happened more than 150 years ago in 1866.

The next total lunar eclipse happening January next year will not be visible from Singapore, and will also last a shorter time, 1hr 2min.

The next total lunar eclipse that can be seen from Singapore will not be for another three years, on May 25, 2021.

Other long total lunar eclipses

Lunar eclipses can last hours, but the time by which total lunar eclipses are normally compared is the length of the totality.

Thus, the duration of the coming eclipse - 103 minutes - really refers only to the period of time from 3.30am and 5.13am on Saturday when the moon will be completely blocked.

In theory, the upper limit of such an eclipse is 107 minutes, making Saturday's eclipse just four minutes shy of the maximum.

On July 16, 2000, a total lunar eclipse lasted 1hr 46.4min, almost achieving the theoretical maximum.

Other notable total lunar eclipses by their duration of totality include ones on Oct 28, 2004 (1hr 20min), Aug 28, 2007 (1hr 30min), and June 15, 2011 (1hr 40min).

7. ECLIPSE CHEAT SHEET

Totality: The period of time during an eclipse where light from the eclipsed body is fully obscured.

Syzygy: From an ancient Greek word meaning "yoked together". A syzygy refers to when three or more celestial bodies form a straight line in space, resulting in an occultation (when a larger body passes in front of a smaller one), a transit (vice versa), or an eclipse.

Penumbra: A half-shadow that occurs when a light source is only partly covered by an object - for example, when the moon obscures part of the sun.

Umbra: The dark centre portion of a shadow.

Apogee: The point in the Moon's orbit which is farthest away from the Earth.

Perigee: The point in the Moon's orbit which is nearest to the Earth.

Sources: National Aeronautics and Space Administration, Science Centre Singapore, TimeAndDate.com, Space.com, CNET.com, Astronomical Society of Singapore, National Geographic, The Washington Post, Smithsonian Magazine, Time Magazine, USA Today

This article was first published in The Straits Times. Permission required for reproduction.