Daytime astronomy
Forget staying up late – All About Space reveals how you can get stuck into observing without waiting until the small hours
Forget staying up late – All About Space reveals how you can get stuck into observing without waiting until the small hours
When most people think of astronomy they picture someone standing outside on a sparkling clear night, gazing up at the wonders of the universe, perhaps using a telescope or pair of binoculars, or just sweeping the night sky with their eyes, taking in the view of stars, planets, the Milky Way and other natural nocturnal wonders. Indeed, a Google image search for ‘astronomy’ will bring up hundreds – even thousands – of pictures of people standing on their own, or in a small group, peering into telescopes beneath a star-dusted sky long after the rest of the world has gone to bed.
As the old joke goes, astronomy is the perfect hobby for three types of people: insomniacs, burglars and vampires. But astronomy doesn’t have to be such an antisocial pastime, and it doesn’t have to be done between sunset and sunrise either.
It’s possible to do astronomy in the daytime; in fact, it’s a good idea for every stargazer and sky-watcher to know what there is to see in the daytime sky because those aforementioned sparkling clear nights are few and far between, and when they eventually arrive our views of celestial phenomena and events are often spoiled because of light pollution. So, what can you see in the daytime sky?
“The good news for anyone wanting to observe the Sun is that it is closer than almost every other astronomical object”
and it is so bright because it is so hot: on its surface the temperature is a stunning 6,000 degrees
Celsius (10,832 degrees Fahrenheit), and its core is even hotter. That means anyone wanting to observe the Sun has to take care and use special equipment and techniques, or else they risk serious eye injury or even permanent blindness. With the right gear, and a healthy amount of caution and common sense, our closest star can be a fascinating object to study before the more distant stars come out.
One simple and safe way of observing the Sun is to simply look at how its shape and colour changes through the day depending on how much cloud it is shining through, how high it is in the sky and so on. When the Sun is high in the sky, or overhead, it is an eye-wateringly bright object. When the Sun is about to set, or has just risen and is low in the sky, it can appear bigger, bloated and more orange in colour than when overhead. This is because we are looking at it through more of the atmosphere, so its light is refracted and distorted, making it appear squashed and bloodshot – and a lot less bright, too.
But even when it is low and dim you still have to be very careful not to look directly at it for more than a moment, or you will risk damage to your eyes.
Because it has always just looked like a bright, blank white disc in the sky, newcomers to astronomy are often amazed to learn that there are fascinating features to be seen on the face of the Sun, and they want to see them. However, to see dramatic solar features such as sunspots, prominences and flares you have to find a way to magnify the Sun’s disc, which is surprisingly small. It’s easy to magnify the Moon or objects in the night sky – all you have to do is look at them through a pair of binoculars or a telescope. But if you use those instruments on the Sun you will concentrate its light and heat into intense beams that will cook your eyes like fried eggs. However, with the right equipment and techniques it is possible to enjoy stunning views of the Sun in a perfectly safe way.
The easiest way is to use solar projection. This involves projecting an image of the Sun onto a
“Using projection you can watch sunspots as they appear from around the limb, then follow them”
suitable surface and studying that image instead of looking directly at the Sun itself. To project a solar image you will need either a pair of binoculars or a small telescope, and a piece of white paper or card to place behind them to use as a screen. By carefully positioning the binoculars or telescope between the Sun and the screen at just the right angle so the Sun’s rays go straight through their lenses and form an image on the screen, you will produce an image of the Sun large enough to show any dark sunspots on its face at that time. Sometimes the Sun is completely blank, so don’t worry if you can’t see anything the first time you look! You can change the size and sharpness of the image by moving the screen closer or further away, and by focusing it in the usual way.
Using projection you can watch sunspots as they appear from around the limb, then follow them as they track across the disc, changing shape and size. The advantages of using solar projection to observe the Sun are many. It is very simple, very quick and cheap, too. It also means several people can see the Sun at the same time. However, it is absolutely vital you don’t look through the projecting equipment or let your skin or anything else wander into the path of the light. Remember how you used to burn paper with the Sun and a magnifying glass when you were younger? Solar projection works on the same principle, so be very careful.
It might seem pretty obvious that if you want a more detailed view of the Sun you will need to magnify it more – but how, if looking directly at the
Sun through a telescope is dangerous? The solution is to fit your telescope with a special filter which reduces its brightness to a fraction of a percent of its usual brightness, then you can use your standard telescope and eyepieces to zoom in on its surface features just as you would zoom in on lunar craters, star clusters or the planets.
The most common and popular type of solar filter is the Mylar filter. Mylar is a very special material that looks deceptively like silver kitchen foil or the material helium balloons are made of, but is in fact a very dense, very lightweight specialised material astronomers have been using for decades now. You can either buy a ready-made Mylar filter produced specifically for your telescope make, model and size, or you can send off for a small sheet of the material and then make your own filter using a hoop of strong cardboard that pushes over the front of your telescope. There are lots of solar filter-making guides available online, or from your local astronomical society.
Using a Mylar solar filter means you can magnify the Sun dozens or even hundreds of times, allowing you to see some very fine detail within and around sunspots and see how they change shape over time, with areas appearing and disappearing, different small groups of sunspots joining up to make larger groups and other solar phenomena. You will also be able to see the ‘granulation’ of the Sun’s surface, which many people think looks like the outer peel of an orange seen through a magnifying glass.
Solar filters are safe as long as they are made of the correct material – so be careful not to buy cheap filters online which may be made from material that will not protect your eyes – fitted properly and are not suffering from general wear and tear – any holes or scratches, however small, could let sunlight into your eyes
“Should you see a brief flash of pink or white you’ll have been lucky enough to
witness a rare solar flare”
and damage them. The main drawbacks with solar filters are their expense compared to simply using projection, and the way that they only allow one person to view the Sun at a time.
There are more than just dark sunspots on the Sun’s surface, but if you want to see the spectacular loops and arches of fiery gas known as prominences, or glimpse bright solar flares, you will need to dig deeper into your pockets.
If you want to see everything the Sun has to offer you will need to invest in, or borrow, a special solar telescope. These instruments are very specialised pieces of equipment featuring built-in filters which are tuned specifically to the ‘Hydrogen-alpha’ – or H-alpha – wavelength. Viewed in H-alpha, the face of the Sun is transformed from a blank, featureless disc to a sunspot-spattered cauldron. If there are any present at the time of viewing, prominences will look like fiery arches, loops or hoops on the Sun’s edge, and should you see a brief flash or flaring of pink or white on the disc you’ll have been lucky enough to witness a rare and powerful solar flare just as it happened.
Solar telescopes offer stunning, detailed views of our nearest star, but they are very expensive, and many people find them difficult to get to grips with. An alternative would be to buy a Hydrogen-alpha filter to go over the front of your telescope, but these are quite expensive too.
If you want to see this kind of detail on the Sun but can’t afford or don’t have access to any of the equipment detailed above, don’t worry! There are many free apps available for your smartphone or tablet and websites you can visit which show ‘live’ views of the Sun in optical and other wavelengths. You can use them to see how spotty the Sun is and watch prominences leap off the Sun and fall back down again.