Finding your way around binocular basics

No 2. in a series created and compiled by Dave Armeson

The NEXT step – going further than naked eye observing…

If you’ve had a few nights out under the stars and learnt a few constellations, then you might wonder what is there to see just below naked-eye limit. Well, rather than plunging in the “deep end” and buying a telescope that might/might not be suitable for you, a prudent step is binoculars. Binoculars bring into view star clusters, glorious Milky Way star fields, Jupiter’s four largest, Galilean moons and of course some craters on the Moon and some of the brighter “Deep Sky” objects like the Andromeda Galaxy.


One great idea is to contact and/or get together with people from your local Astronomical Society and talk to them about binoculars – the knowledge they have can save you from making a sometimes costly mistake (the same applies to buying your first telescope – more about this in a future article).

Why binoculars…?

Binoculars offer a number of advantages that make them superior to larger telescopes. In fact, binoculars could be looked as two smaller telescopes that are joined together to give your eyes stereo images. They have three main benefits over telescopes: cost, portability and ease of use.

Binocular types: porro prism and roof prism

The most popular and probably best type of binoculars for astronomy are called porro prism binoculars and look like what you imagine when you think about binoculars. The other type of binoculars is the “straight through” type which are called roof prism binoculars. Porro prism binoculars will give a 12% to 15% brighter image than roof prism binoculars as roof prism binoculars employs silvered surfaces that reduce light transmission by 12% to 15%. Roof-prisms designs also require tighter tolerances for alignment of their optical elements. This adds to their expense since the design requires them to use fixed elements that need to be set to a high degree at the factory.

porro prism binoculars
Porro prism binoculars
roof prism binoculars
Roof prism binoculars

Magnification and field of view

Binocular magnification
Binocular magnification

On the back of any pair of binoculars are two numbers. The first number denotes the magnification of the binoculars themselves and the second number is the size of the front lens in mm. For example in this image they are 7x magnifying with a front lens of 50mm diameter. Other popular sizes are 6x or 7x 35mm binoculars.

Easy binocular targets

The Pleiades (Seven Sisters)

The Pleiades open cluster
The Pleiades open cluster (click image to enlarge)

During the autumn and winter months one of the most stunning visual sights is the Pleiades (The Seven Sisters) star cluster in the constellation of Taurus. They are 2,644 million million miles away. With the naked eye you can see a group of up to 10 to 12 stars under a clear dark sky. In binoculars the view is transformed into something like this image.

The Andromeda Galaxy.

Andromeda Galaxy
Andromeda Galaxy (click image to enlarge)

This is the nearest external galaxy to our own Milky Way and lies at a distance of about 2.5 million light years from Earth. It contains about 250 billion stars/suns.

Finder chart for the Andromeda Galaxy
Finder chart for the Andromeda Galaxy (click image to enlarge)

Remember when you are looking at Andromeda in your binoculars, the starlight from the billions of stars that make up that galaxy has been travelling through space for the last 2.5 million years at the speed of light to land on your retina – so you are looking back in time….!!!

Print version of this post (PDF format)

Finding your way around the night sky

No 1. in a series created and compiled by Dave Armeson

First steps…

It’s not as difficult as you first think!

Starting out in astronomy at first seems a very daunting prospect. When I first got into stargazing nearly 40 years ago  I thought this is going to be difficult – but I was pleasantly surprised. When you learn just a few constellations it is surprising how everything else tends to start to fall into place – and a few months of perseverance you will start to gain a very satisfying working knowledge of the night sky. You should be able to identify nearly all the northern sky star patterns within a year of dedicated looking.

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The ultimate history of the York Astronomical Society

Martin Dawson joined the York Astronomical Society in 1973 shortly after the society was formed and has been a member ever since. He kept an occasional diary of events from that time. Some of the entries bear a similarity to current happenings at the Society: meetings, talks and working parties at the observatory, then at Acaster Airfield. An example entry:

7 Jan 1977 – ‘YAS Member Mrs. Gibson presented her talk on her trip to West Africa to see the 1976 October eclipse. 0.90p made in raffle (1.75) Planisphere as prize.’

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Blast from the past – Newsletter no.3 January 1974

York Astro member Martin Dawson, has sent us a copy of the Society’s newsletter from 1974, two years after the Society was formed. Although the newsletter was printed on old technology with hand drawn illustrations, the topics covered would be familiar to members now; reports on recent talks, what’s to be observed that month and progress with the observatory. Back then, meetings were held at the Railway Institute and planning permission for the observatory had been obtained, plus the Society has acquired a 12.5″ reflecting telescope – wonder what happened to that.

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Lunar Eclipse – York Astro media stars

Martin Dawson makes the front page

People in York (well, those prepared to be up through the night) were rewarded with a spectacular view of the lunar eclipse on Monday morning. I feel sorry for some I know who got up through the night and see clouds, only to go back to bed to miss the spectacle when they cleared. York Astro members were busy posting their photographs to social media and Martin Dawson had a photo selected for the York Press lunar eclipse gallery and then with a front page picture and accreditation for him and the Society. Continue reading

Bulletin – December 2018

End of an Era

The YAS Rufforth Observatory is no more!

The remaining PortaKabin unit has been dismantled and suitable materials recovered for recycling or appropriate disposal.  The remaining rotted wood has been burnt. Here you can see Martin Whipp in nostalgic mood watching the burning embers – Martin was there at the beginning and at the end.

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Bulletin November 2018

October in Brief…..

AGM and Informal, A Moving Experience, Knavesmire Exceeds and Honest Stargazing

October 5th Meeting #1002 AGM and Informal

The AGM was the first proper general meeting since becoming a charity. There were just four items of business:

  • Minutes of AGM 1st December, 2017
  • Trustees’ Annual Report
  • Trustees’ Annual Financial Report
  • Trustee Elections

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