How to safely view the Mercury Transit

By Natasha Mendes

Photograph mosaic image of the planet Mercury. CC-0 Universe today

Photograph mosaic image of the planet Mercury. CC-0 Universe today

On Monday 9th May 2016 between 12:00 Noon and 7:30pm the transit of Mercury across our Sun will be visible in the UK. Our new science made simple branch in Milton Keynes will be hosting a free science event along side the Open University, however, there is still plenty you can do if you are not local to us.

Read on to find out how you can observe this astronomical event safely at home.

There are three safe methods you can observe the Mercury transit yourself at home or wherever you may be. All you need is a pair of binoculars or a telescope:

1. Using binoculars

Most binoculars are suitable for viewing the Mercury transit on Monday. You will need the magnification provided by the binoculars in order to observe the transit, but you cannot view directly through binoculars without an appropriate filter (see below) as the Sun’s UV rays are  damaging to the eyes.

Instead of observing the transit directly through the binoculars, you will need to have them mounted outside on a tripod or stand pointing towards the sun with the eye pieces directed towards a mounted piece of plain white card/paper or placed on the floor.

To create a clearer picture you can make a shadow by using card cut to fit around the end of the binoculars as seen in the image below. This will make observing the transit on the projected onto paper much clearer.

Mercury will move east to west across the sun yet this image can be reversed when observed in this way. The projected image may be flipped horizontally and/or vertically, depending upon the binoculars’ optical arrangement. Because a binocular has two eye lenses you will see two identical projected images of the Mercury transit on the white card/paper. Most individuals will cover one of the binoculars’ lenses with a lens cap when viewing so they are only projecting one image.

Binoculars set up for transit viewing. CC Arts and Stars.

Binoculars set up for transit viewing. CC Arts and Stars.

2. Using a refracting telescope

The set up is much the same as with the binoculars. Again, you cannot look directly through the telescope when pointed at the Sun, therefore, the image is directed onto a piece or white card or paper. Again you can use card to create a shadow to see the transit more clearly.

3. Using a solar filter on your telescope (either reflecting/refracting)

A Celestron telescope with a aluminised solar filter attached to the front. CC - Celestron

A Celestron telescope with a aluminised solar filter attached to the front. CC – Celestron

The Mercury transit can also be observed safely through a telescope by attaching an aluminized solar filter to the front of the telescope and ahead of the object glass. Depending upon the manufacturer’s specific design, the Sun may appear to be pale blue, yellow, or white, however, their purpose is the same: to filter the ultra violet rays so that it is safe to view the sun.

It is important to be mindful of purchasing second hand solar filters or borrowing them. You will need to check that the filter is not damaged or scratched which may compromise the safety.

warningYou must never look at the sun directly without the correct protective eye wear.

Wearing eclipse viewing glasses will not work; Mercury is too small for the transit to be visible to the naked eye and requires equipment to magnify it. Never look directly at the Sun without protection. Only do so with a telescope or binoculars if you are using the correct filters and equipment. Looking directly at the Sun without protection can cause blindness. It is advisable not to point optical equipment such as telescopes and binoculars at the Sun for long periods of time as they can create hot spots on to the surfaces they are projecting on to.

Other ways to observe the transit

Lots of local astronomy clubs and societies host public events and may be offering people a chance to view the transit with their equipment in your area. Search online to find your local Amateur Astronomy Society and check the website of your local  museum to find out about public events in your area.

If you are near Milton Keynes on the 9th May 2016, drop in and see us at this free science event in celebration of the Mercury Transit across the Sun at the Open University. We will be showcasing some of our 3D space films and virtual reality space apps along with other exciting space themed workshops.

There are also a few organisations hosting live broadcasts online, including this one from Exeter Observatory.



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