When To Go Out

Astronomy, unless you’re looking at the sun, means going out at night. There are a few astronomical sights that are visible in the day time – Venus, the Moon the odd comet, but generally it’s in the dark that you’ll actually be able to see stuff.

Weather is a deciding factor. This is the ultimate fair-weather hobby because clouds will stop you from being able to see the sky and hence the stars. Even when it’s clear, not all nights are the same. High atmospheric turbulence can ruin views of the planets and murk and mistiness make deep sky astronomy impossible.

The other big decision to make is whether to be a lark or an owl. The sky changes markedly over the course of a night and there are things visible in the morning that you wouldn’t see in the evening. Personally I prefer observing in the evening. Everything ends up in the evening skies at one time or another after all.

In this blog, nearly all the objects described should be prominent at 9.30pm. In the summer the sun sets late, so you’ll have to stay up later. All these objects will require half an hour of your time, so once you’ve observed you can get back inside for that last cup of cocoa / tea / gin before climbing the stairs to Bedfordshire. Unless like me you live in a flat.

The seasons all have rather a different character in terms of what’s visible, so here’s a little potted guide to astronomical seasonality:

·         Spring – My favourite time of the year. Early Spring you still see the winter constellations and late Spring you start to see the summer ones. One drawback is that in Spring we’re looking up out of the Milky Way, mostly at faint galaxies, out of the reach of urban astronomers. There are a fair few globular star clusters around though. And sunset is still early while the nights aren’t excruciatingly cold.

·         Summer – I love observing in the summer. It’s the time when the galactic centre in Sagittarius is visible. The most obvious stars form a triangle dubbed, “The Summer Triangle” – Deneb, Vega and Altair. The Milky Way runs through this area, with many of the finest nebulae and clusters. Nights are at their warmest, although an extra layer is often necessary. The only problem is the length of the night. In June it never gets fully dark, and often you need to stay up until gone 11pm to see anything.

·         Autumn – Not a big fan of autumn for astronomy. It’s the other time of year when you’re looking out of the plane of the galaxy, so all there is to look at are a few globular clusters and galaxies. To make up for it, a lot of star clusters are at their zenith, and some of the most impressive clusters and galaxies are visible. Look out for the square of Pegasus. Nights are drawing in too but aren’t so cold, although fog is often a problem.

  

         Winter – Winter is great, as long as you can take the cold. In Britain the climate is not conducive to astronomy all the time but when it clears, boy is it clear. You’re looking in to a spiral arm although I find there’s less to see now than in summer. Having said that, the incomparable Orion Nebula is high overhead, and that alone is a sight worth schlepping out for on a cold, crisp evening.

Where to Go

Right, so now you’ve chosen your weapon, where are you going to stick it? Cue the inevitable Uranus jokes.

One of the most important things to decide is where to actually do your astronomy. You don’t really want to stray too far from home, but you do at least want to make the trip outside worthwhile. Balancing these two factors is a tricky thing.

First, let’s consider what dark means. You’ll probably think of it as an absence of light, but your astronomer would think of it in terms of how many things in space they can see. The darker a place is the better it is for doing astronomy. We can’t always get to somewhere properly dark but now is a good time to find out where the darkest place near you is. There’s also some jargon we need to get used to:

• Magnitude  – how bright an object is. The lower the magnitude, the brighter the object. Just to confuse matters further it’s on a logarithmic scale, so a magnitude difference of one represents a roughly 2.5x difference in brightness. Confused? Don’t be. This blog deals in terms of what you can see with a street light next to you etc. I won’t be using numbers so you don’t need to breathe into the paper bag any more.
• Naked Eye Limiting Magnitude (NELM) – the magnitude of the dimmest thing you can see. NELM in the city is terrible – in central London you’ll be lucky to see more than about 15 stars on a clear night. In Bushy Park I can pick out all the constellations, so the NELM is lower (i.e. I can see dimmer objects).
• Light Pollution (LP) – the bane of our astronomical experience. Streetlights are there to light the ground but half their light goes into the sky. The sodium in the lamps has that awful orange hue, and you can buy filters for telescopes to combat it.

The horrors of Light Pollution - seen here from the doorstep obscuring Ursa Minor.

 Transparency and Seeing – not all nights are the same. The differences in the quality of sky are down to amount of cloud (Transparency) and atmospheric turbulence (Seeing).

• Dark Adaption – the rod cells in the retina are extremely sensitive, especially to blue light. These are the cells that allow you to see in the dark because the colour sensitive cones need lots of light to work. When the rods are exposed to brighter light sources then they get overloaded and stop working. It takes roughly half an hour for the neurotransmitting chemicals in them to settle down, so the longer you stay in the dark, the better you can see. This is also why astronomers use a red light, to avoid bleaching these cells.
• Surface brightness – Very important for urban astronomy, this is a measure of how spread out the light is coming from the object. As an example, there are two galaxies I looked for one night in the park. M33 is bright, around mag. 5, while M77 is dim at mag. 8. But I could see M77 and not M33 – the reason is that M33 is very much bigger so the light is so spread out you can’t pick out the galaxy against the light pollution. M33 is notorious for being hard to spot – go to the dark of somewhere like Exmoor and it’s very easy to see, but even a little light pollution will make it impossible. This is also where dark adaption is important.

So the take home point is that the less light the better, and that also the choice of objects is key. I’m only going to highlight things that can be seen with NELM of about 4.0 – 4.5, a typical suburban sky. If you’re somewhere rural your views will be very much better.

So where do I do most of my star-gazing?

·        The front step – our flat is blessed with a small patch of gravel, just large enough for the ST80. There is a street light right next to it, so I don’t need a torch to look at the star map. It benefits from being close to the flat but the light pollution is pretty bad and I have severely restricted view of the sky. Bushy Park – Away from the street lighting, the park does get pretty dark. There are a few other considerations if you’re going somewhere like this:

o   It’s a way from the flat so I am limited as to what I can lug down there.

o   They close it after 10.30pm in September and November to cull the deer.

o   It’s full of deer – being native to the New Forest I’m used to deer. They don’t see me as a threat so I can happily observe with them right next to me.

o   A bigger concern is violent humans. Everyone I’ve met while out star-gazing has been either friendly or done that London thing of ignoring the strange chap in case he starts trying to converse… Be sensible – always tell someone where you’re going and if possible go with someone else. If you’re not sure then don’t go – you might not pick out the Crab Nebula on your front porch but it’s far more important to feel safe.

Bushy is the darkest place in Greater London I know of – On one extremely transparent night I did manage to pick out the Milky Way as a faint glow overhead. This is a very rare occurrence, but just goes to show that it's always worth a try!

Choose Your Weapon!

The most bewildering question for a budding amateur is which telescope to buy. Really, your first question should be, “Do I need a telescope?” Often the answer is no. This blog is intended to be an introduction to observational astronomy, so you don’t need a telescope to follow it. For anyone who does want a 'scope, here are my thoughts on this perennial question.

The best telescope is the one that you get out and use. Rather than rehashing information about types of telescope, I’m going to talk about my own equipment. Shop around for your perfect instrument; visit a star party or observing event so you can look down some ‘scopes and see how big they are in the flesh. Let's start by considering the most frequently recommended telescope.

Use a web forum like Stargazer’s Lounge, ask “What is the best telescope for a beginner?” and the answer always comes out the same – the best instrument for the beginner, by a mile, is an 8’’ Dobsonian. The Dobsonian mount is alt-azimuth – basically it has two axes: left and right, up and down. Very simple to use, they offer a large aperture at a low price. Aperture, if you’re not down with the jargon, is the width of the hole and hence the optics, in this case a mirror at the bottom of the tube. They cost under £300, are large enough to access thousands of objects and show lots of detail. They are brilliant.

But there's a snag.

They weigh in at 23kg. My main observing site is a park 500 yards from my flat. Even if I manage to wrestle the damn thing outside, I’m not going to get it to the park on foot. Therefore an 8’’ Dobsonian would be the wrong choice for me.

Here’s my ‘scope:

Lots of fun to be had at night in the park! This is on a spotter scope tripod borrowed from work - a nice option for a simple mounting, but you can't point it at the zenith (i.e. straight up).

This is a Skywatcher Startravel 80, a wide-field refractor. Refractors are the classic telescope design, using lenses to collect and focus light. 3'' is small but at around 6kg in weight I can actually get it to where I want to use it. So for me it’s perfect. It has its cons: the aperture is small, so I can’t find as much as I’d like, it suffers from false colour and it’s a short focal length telescope – that means it’s great for large things, but doesn't magnify much, so it’s less suited to looking at planets. Here's a low-quality snap of Saturn to give you an idea, taken using my wife's iPhone through the eyepiece:

n.b. when I was looking down the eyepiece we could see the rings and their shadow cast on the planet!

Mine is equatorially mounted, tilted so that it can track objects as they move across the celestial globe. These mounts do take some getting used to; I learned to handle one a long time ago and wouldn’t want it any other way, but it's not as intuitive as the Dobsonian.

What is a small ‘scope like this capable of?

• The Moon – plenty of detail to be seen, although not as fine as a larger scope

• Planets – not its forté; see the above photo

• Star clusters, nebulae and galaxies – Only the brightest are visible. Some objects require a dark sky too. You can forget seeing spiral arms of galaxies, but its brilliant on big star clusters, and the wide-field of view makes it easy to find stuff.

They cost roughly £130, so they won’t break the bank either.

If you’re looking for something for a child, then consider one of the Tabletop Dobsonian designs, such as the Heritage 130P, a good choice for portable astronomers too. The Dobsonian mounting is easy to use, at 6kg it's light enough to be handled independently and with 5’’ of aperture it'll show enough detail they won't get bored after five minutes.

I also use a pair of Nikon 10x40 binoculars. I’m not a fan of binoculars for astronomy because I can't hold them still enough, but if you’re a casual observer and want something ultra-portable, they’re great. They’re also brilliant for learning the sky. In this blog I’ll talk a lot about the view through binoculars, and even a small pair will show you plenty. For children under eight, don’t bother with a telescope for now, get them binoculars instead. That way they can learn the sky and you can see whether its a lasting passion or a passing fad for them!

For further information, try one of the following links:

Sky At Night Magazine's take on which telescope to buy

Comprehensive Buying Advice from the U.S. 

Telescope Simulator gizmo - shows you what stuff looks through a telescope of given apeture and focal length