EXPLORE THE HEAVENS
It’s time to discover and explore the night sky with a little open-source software, your own two eyes, and the help of Mike Bedford
It’s time to discover and explore the night sky with a little open-source software.
“SPACE IS BIG. Really big. You just won’t believe how vastly hugely mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” OK, so these words from Douglas Adams’s spoof scifi novel The Hitchhikers’ Guide to the
Galaxy might have been intended as a bit of silliness, but the sentiment is true.
Based on the latest data from the Hubble Space Telescope, astronomers estimate there are 700 sextillion (that’s 700 thousand billion billion) stars in the visible universe. Trying to get your head around such a vast number of objects— or even just those that can be seen from Earth with the naked eye—is, well, mindboggling. But we’re here to help.
Our aim is to aid those who are fascinated by the sky at night, but know little about those countless pin pricks of light on display, to take their first steps in practical astronomy. First, we’ll see how open-source software can help you plan your star-gazing by showing you what will be visible at any time, and where to look. Then, armed with this information, we’ll provide you with some practical guidance on how to observe some of these astronomical objects with nothing more than a pair of binoculars.
Some objects will never look like more than tiny points of light, so next we’ll use software to shed more light on these alien worlds, even showing you how they’d look if you were to go there.
The software we’ve chosen to help you plan a night of practical astronomy is the highly regarded open-source Stellarium. It generates an image of the sky as it would appear from any point on the Earth’s surface, at any time—past, present, or future. Usually, you’d use it to show the night sky as it will appear at your planned observation location at the current time. However, there will be times when you’ll want to see the sky as it will look a short time into the future, as an aid to planning your observations.
GETTHE MOSTFROM STELLARIUM
Stellarium is unusual in not having a conventional menu bar. Instead, it’s driven mainly via two toolbars, which are normally hidden. They are displayed by moving the pointer to the bottom or left of the screen, near the bottom-left corner. Select a town or city close to your location, and the time you’re interested in, using options in the left-hand toolbar.
You can also select which types of objects to display (stars, planets, moons, or asteroids), and filter the display labels according to the brightness of the objects. With this option, you can find a compromise between not being able to identify objects you’re interested in, and seeing so many labels that the screen is utterly confusing. Another option is to display the lines that define constellations, to show their names, and even add an image. So, for example, having displayed the lines and the name of the constellation Orion, you can superimpose the artwork of the hunter. Of course, constellations have no astronomical reality. So, for example, the seven stars that constitute the Big Dipper, which form part of the constellation Ursa Major, appear to be close together, but this is an illusion, as they vary from 58 to 124 light years away (300–750 trillion miles). Often, stars in a constellation appear to be of similar brightness because the more distant stars are larger than the closer ones.
As a final comment on Stellarium, it often displays stars that you can’t see in the sky with the naked eye. This might seem pointless, but more objects are visible if you use binoculars, and more still appear if you use a telescope. In addition, Stellarium can also display objects that you can’t always on screen because they’re so faint. For this reason, the authors suggest using Stellarium in a darkened room.
PRACTICAL OBSERVATION
The easiest way to start your voyage of discovery is to observe the night sky outside your home. However, unless you live away from centers of population, the sky will suffer from
light pollution, so you’ll struggle to see some objects that would be clearly visible in more remote areas. The upshot of this is that you might need to put your laptop in the car, and go in search of darker skies.
It’s not just the sky that can hinder your observations; your own eyes can work against you. When you first go out into the dark, your eyes won’t be sensitive to dim objects. For this reason, unless you’re looking for something bright, such as the moon, Mars, Saturn, or Jupiter, you’ll need to wait a few minutes for your eyes to adjust. Remember that this adaptation is reversed if you look at anything bright, and that includes your laptop screen. So, if you want to refer to Stellarium during your observations, select its night vision display mode, which renders the sky in dark red on black.
Stellarium shows compass bearings, so you know which direction to look to see a given object. Unless you know where each of the compass points lies, you’ll need to use a compass or a compass app on your smartphone, to figure out where to look. Alternatively, there are Android apps that provide similar functionality to Stellarium, but which use your phone’s sensors, so the display reflects the actual direction the phone is pointing. We used SkEye, but there are loads of others, many of them free, so you can try them out to see which you like best.
Now you know what you ought to be able to see, and where to look, we need to cover the practicalities of observing astronomical objects. To start, we suggest you use nothing more than your own eyes. You won’t need any instructions, or the help of Stellarium, to see the moon, but do spend a few minutes to identify those bright planets that might be visible, and here we include Venus, Mars, Jupiter, and Saturn. Next, try looking for some of the constellations that Stellarium shows you.
The next step is to use binoculars. These will help you to see lots of objects that Stellarium identifies, but are invisible to the naked eye. However, some of the most interesting objects to observe when you’re starting out are ones you’ve already identified with the naked eye, because you can often see so much more.
We recommend starting with the moon, where binoculars can help you to differentiate the dark-colored plains from the light-colored highlands, and reveal some of its many craters. You could also turn your attention to the red planet, Mars, but although your binoculars will show it as a larger and redder dot, you won’t see any additional detail.
However, for something that’s almost guaranteed to amaze you, if you’ve not seen it before, train your binoculars on Jupiter. With the naked eye, it’s just a dot, but through binoculars, that dot has up to four smaller dots close by. These dots, which shift in position with respect to Jupiter over time, and are sometimes behind the planet and hence invisible, are called Callisto, Europa, Ganymede, and Io. These are the four largest of Jupiter’s many moons, and are known as the Galilean moons, after their discoverer.
ONWARD TO VENUS!
Now on to a couple of more challenging observations, and here, if your binoculars have a suitable mount, it would help to attach them to a tripod to help keep the image steady. First, take a look at Venus. If your binoculars are good enough, and depending on the date, instead of the dot you saw with your naked eyes, it might appear as a crescent or a half circle. This is because, just like the moon, the planet Venus displays phases. And second, turn your attention to Saturn. If you notice that it isn’t perfectly circular, or if it appears to have ears, you’re actually seeing its rings, even though you’d need a telescope to see them more clearly. You might also be able to see Saturn’s brightest moon, Titan.
As we turn our attention beyond the solar system, binoculars are again able to reveal detail that is otherwise invisible. For example, not all objects that appear to the naked eye as a single dot of light are what they seem. Some objects that look like stars are actually double stars, and appear as such through binoculars. In some cases, the two stars only appear to be close together from our viewpoint on Earth, while others are actually a pair of stars orbiting around each other.
A good one to spot is Mizar in the handle of the Big Dipper, although some people
can see two stars unaided. However, one of the most spectacular double stars is Albireo in the constellation of Cygnus. You’ll have to wait until summer, and you need a good pair of binoculars to see it, but it’s particularly spectacular because the two stars are different colors—blue and amber.
ZOOMING IN WITH CELESTIA
Having seen some of the remarkable objects in our solar system and beyond with your own eyes, perhaps aided and abetted by a pair of binoculars, you’ll surely be interested to learn more about some of these planets, moons, and stars. After all, even with good binoculars, many of them still only appear as specks of light, and that begs the question of what they would really look like if you were able to visit them.
To help answer that question, we’re turning our attention to another opensource package, called Celestia. Before we get started, though, we should point out that, despite it having an enthusiastic following, it’s not updated as frequently as we might hope, with the result that it doesn’t appear in some of the more recent Linux repositories (if you’re exploring the heavens with an open-source bent). You can grab the latest version of Celestia for Windows by pointing your browser of choice at www.celestia.space, clicking the download tab at the top of the page, and then electing to download the newest (or if you’d prefer, the previous) build.
When you first start Celestia, you see an image of the Earth as it would appear from orbit and, already, you’re seeing something markedly different from the view provided by Stellarium, which shows you how the sky looks from the Earth’s surface. Indeed, Celestia enables you to define a viewpoint anywhere in the solar system or, for that matter, far beyond. For views of the planets in our solar system and their moons, the view that you see uses actual photography of those bodies, as captured by NASA’s various planetary probes. And for more distant objects that spacecraft have never visited, the image you see is based on the scientific view of what they probably look like.
Let’s imagine that you observed the planet Jupiter with your naked eyes, and then discovered its four Galilean moons using binoculars. In that case, you could well be interested in seeing what those white dots would really look like from a spacecraft in close proximity.
Let’s start with Io. Search for it in the “Navigation” menu, then select “Goto Object.” Io is displayed from some arbitrary distance, but if it’s too small, you can select a smaller distance in the “Goto Object” window. When you start to see the detail on the surface of Io, you’ll notice several small dark circles, which are volcanoes. It transpires that Io is the only known object in the solar system, other than the Earth, to have active volcanoes.
So far, you’ve seen Io, but depending on when you view it, it might not be obvious that it’s orbiting Jupiter. Probably the best way to address this is to fast-forward, by repeatedly using the “10x Faster” option in the “Time” menu—eventually, you’ll see Io in relation to Jupiter.
Going beyond Io, you really ought to take a look at Jupiter’s other large moons. If you expected that every Jovian moon would look similar, you’ll be in for a surprise. Also, as with Stellarium, you have total control over what’s displayed on screen. You can turn the outlines of constellations on and off, choose what, if any, types of objects to label, and display orbits, information on the selected object, and so much more.
In our use of Celestia so far, we’ve positioned ourselves at fixed points in space to get a good view of the objects we’re interested in. This is just a start, though, and if you want something a little more interactive, you can even view the heavens while taking the controls of a simulated spacecraft. In addition to flying between planets and stars, you can go into orbit around them, and you can even land on the surface of planets and moons. We’ll leave you to figure all this out yourself, for which you’ll probably need to consult the comprehensive user guide at www.celestiamotherlode.net/catalog/ documentation.html.
Celestia will keep you entertained for countless hours, just by trying things out yourself. However, your enjoyment of Celestia, and the whole universe for that matter, can be enhanced by taking advantage of the contributions of others. A useful feature of Celestia is the ability to create and play back scripts, something that lots of users have employed to produce animated tours of parts of the solar system and beyond. The best place to find add-ons for Celestia is www.
celestiamotherlode.net. We’re confident that you’ll find plenty here to enhance your appreciation of the sky at night, and help you to better understand the remarkable worlds that are just waiting to be discovered.