Constellation of the Month – August: Lyra

August marks the return of proper darkness down south, or as proper as darkness gets in Lahndahn Town. This is the time when the serious astronomer dusts down their telescope and prepares to sally forth once more…

 
So, in a new feature on this blog, I'm going to present a monthly guide to one constellation. And to kick us off I choose… Lyra, the Lyre.

 

The Summer Triangle

Lyra

Lyres are maybe not familiar instruments to us these days. Basically, they're like little harps, and it doesn't actually take much imagination to see a Lyre in this pattern in the sky. This is quite rare for astronomy, where four really faint stars can make up the constellation of the Giraffe. To find Lyra you'll need to look high in the sky for a large triangle of stars colloquially known as the "Summer Triangle." The highest one is Deneb, the lowest is Altair and the middle one is Vega, and this last one is the brightest star in Lyra. In fact it happens to be the fifth brightest star in the sky. Next to Vega you'll be able to make out a parallelogram (Going back to those school maths classes) of four other stars, and this makes up the bulk of the constellation.

Image credit: free software Stellarium, http://stellarium.org

It was one of the original 48 star-patterns named by Ptolemy the Greek-Egyptian astronomer around the 2^nd Century. You might be wondering whose Lyre it is – it belonged to the mythical Greek musician Orpheus whose musical abilities were such that he could charm all living things and even stones. Quite why he wanted to charm rocks is unknown – go with it, this is Greek myth. He was eventually killed and his Lyre was thrown in the river – Zeus ordered an eagle to find it and then put both Lyre and Eagle into the heavens where they because the constellations of Lyra and Aquila. Why an eagle? That's not an aquatic bird – an osprey would have been a far superior choice. Or a gannet.

 
Joking aside, Lyra packs quite a punch for such a titchy constellation. Here's a guided tour of the highlights:

• Vega – Alpha Lyrae is kind of a gold standard for stars because it's at magnitude 0 (Well 0.04 to be precise). The brightness of all other stars is measured relative to the brightness of Vega, which is something of a claim to fame. Look at it through a telescope and you'll see it's pretty bright and a cold bluey-white colour. Most of its interesting facets are invisible to the eye, even with a telescope – it lies at 25 light years so is pretty close by, and it's twice the mass of the sun. This means that its lifespan will be a tenth of our own star's. Most bizarrely, its rotation is so rapid that it bulges outwards at the equator, something that can only be inferred rather than viewed directly. 
• Epsilon Lyrae – The Double-Double – A lot of stars are not solitary like our sun, but are double star systems, mutually bound together by gravity. Epsilon Lyrae outdoes these though because it's a quadruple star. With the naked eye it appears as a single star above and to the east of Vega. Through binoculars you get a different story as it resolves into two separate stars staring down at you like cat's eyes. But with a telescope and a bit of magnification you'll see that each star is actually two stars, very close together. It can be resolved easily, even from London, and is a bit of a classic test of the seeing conditions. 
• M56 – An example of a globular cluster, a dense conglomeration of ancient stars formed at a very early stage in the history of the universe. They hover round our galaxy like a halo of flies, and M56 is one of the brighter ones, although still a challenging object here in London. There's not terribly much more to say about it – you really want a telescope to find it and with even my 6'' Dob all I get is a fuzzy disc of light. 

  

  The Ring Nebula - Image Credit: NASA

• M57 - The Ring Nebula – Saving the best until last, we finish with the classic example of a planetary nebula. Once again science seeks to confuse us because it has nothing to do with planets. Planetary nebulae present discs when viewed through a telescope so look like tenuous planets. The Ring is a bit special though and one of my top objects for viewing under light polluted skies. Although it's relatively faint at magnitude 9, it's small so its light is concentrated in one place – high surface brightness. It lies between the bottom two stars of the parallelogram, pretty much midway, but you need a telescope to see its secrets. With low power it looks like a faint fuzzy star, but crank up the magnification and strange things happen… With averted vision (I.e. not looking directly at it) you'll see not a disc, but a tiny ring of light. Using a nebula filter will enhance this effect, and even my little 3'' refractor shows it. The Ring Nebula is the remains of a star – when stars of around the mass of our sun run out of fuel they first expand to use up their supply of helium before shrugging off their outer layers leaving a puffy planetary nebula and a faint white dwarf star; all that remains of the core of the star. It's slightly macabre to think that one day our sun might look like this – makes you want to enjoy life and look after our planet because it's the only one we've got…

Saturn Return!

A little googling has shown me that a “Saturn Return” is some kind of astrological term. I’m sure we don’t want that kind of thing on here. Just to reassure you, I’m not about to get all Mystic Meg on you, I was actually referencing an REM song…

Seriously though, this week I’m focusing on Saturn, the famous ringed planet. It’s just passed opposition so now is a great time to get out there and see what is regarded to be one of the wonders of the solar system. And hurry to see it while you can because from this year until the early 2020’s, Saturn is going to be a difficult planet to see from Northern latitudes as it skirts our horizon in the constellations of Scorpius and Sagittarius…

Saturn, the Ringed Planet - Photo by NASA

The ringed planet is the faintest of the naked eye planets, getting close to magnitude 0 at best. That means that although its fainter than the others (And it’s debatable whether Mercury could be classed as easier to see) it’s still a pretty bright object. At the moment it’s lurking in Libra, so miles from any other bright stars except for Spica, the brightest star in the constellation of Virgo.

Naked Eye

Saturn is most prominent at about Midnight, fairly high and due south. It’s a yellowy star and brighter than anything else around it, but otherwise not immediately interesting.

Image thanks to Stellarium

 

Binoculars

Once you get Saturn in the binoculars you may be disappointed to find that you can’t see the famous ring system. Even very large binoculars will show the planet as an oval at best. You might be able to make out a small orange dot close to Saturn though – this is Titan, its largest moon, and one of the largest in the solar system. Its surface is permanently shrouded in methane clouds that tint it orange, and beneath them lies an ocean of liquid methane.

Telescope

With a telescope Saturn isn’t just interesting, it’s one of the most beautiful objects in the solar system. Even a modest aperture will show you the famous rings. For a long time people didn’t know what the rings were – astronomers even speculated that they were solid objects. They did observe that the rings change their orientation to us over time. At present they’re angled towards us so we see their full extent – at this time with good seeing and enough aperture you can make out the gap between the two main ring systems, the Cassini Division. In about ten years’ time, as the planet wobbles on its axis, the rings will be edge on, appearing as a long line, and for a while they’ll be completely invisible. This is the best time to look for the other moons; Dione, Tethys, Rhea and Enceladus, if your aperture is up to it. You can see them now from time to time, but the rings will obscure them every so often. Probably the other most bizarre moon of Saturn (And it has 53 named moons) is Iapetus, which featured in Arthur C Clarke’s novelisation of 2001: A Space Odyssey* – half of it is highly reflective while the other half is quite dark. When the reflective side is turned towards us it’s easy to see, but at other times it becomes quite hard.

Freaky Iapetus - Photo by NASA/JPL/Space Science Institute

Aside from the impressive ring system, Saturn doesn’t show much more. There is some banding, under clear skies, but mostly it’s the rings that steal the show.

* The location of the final monolith to Iapetus in the book is because it was developed concurrently with the film, but in the later novels Clarke sticks with the film’s location orbiting Jupiter. Conversely the famous line, “Oh my God, it’s full of stars,” only appears in the book, but was used in the film’s sequel 2010.

Mars Attacks!

It’s been a long time since I lasted posted a blog entry. It hasn’t been a great year so far with precious few observing opportunities around. The cloud has felt nearly constant for the first quarter of the year, but there have been a few chances to get out under the stars in between. The moral of the story is to not get downhearted and, even if it's only half an hour, grab the opportunities while you can!

This week is a great one to really make an effort, if the skies clear, because this week sees Mars at Opposition. That means it makes its two-yearly closest approach to Earth, so appears at its largest in our skies. The next one isn’t until 2016, so if you get a chance to get out and observe, make Mars your priority target.

Photo by NASA

The Red Planet has long been a tantalising object – its colour gave it an association with the God of War, and Holst certainly agreed when he wrote the portentous opener to the Planet’s Suite, “Mars, Bringer of War.” It became the abode of alien intellects “Cool and vast,” according to H. G. Wells in “War of the Worlds,” and swiftly became the place where green men from outer space would come from for a spot of invading. Later on things got a little less highbrow with Irish rock band Ash celebrating a “Girl from Mars” and Tim Burton’s execrable “Mars Attacks!” film. Even now Mars holds a certain fascination with us on Earth, and as I type a number of missions are underway on and around its surface.

Why Mars is so interesting is open to conjecture. It's about half the size of Earth (Venus is nearly the same size as us) and in distance terms it varies from around 0.6 AU to nearly 2.0 AU from us (Again, Venus is closer...). And yet it may have harboured life at some point in the past, or even now. There is much evidence of liquid water on its surface, with huge river canyons carved through the dusty red landscape. It has ice-caps like our planet, although they are made of dry ice, solid carbon dioxide. And interestingly it has active volcanoes, including the highest mountain in the solar system, Olympus Mons, of fundamental importance in the creation of an atmosphere. Any discovery of life, past or present, would be profound for us, taking away Earth’s special place as the abode of life in the universe.

Unfortunately, as far as observational astronomy goes, it isn’t exactly a thrilling target, usually looking like a small orange disk with no discernable detail whatsoever. To add to the fun it has frequent dust storms raging across its surface that mask the features with even more impenetrable orange. In short, Mars is one of the most disappointing things you will view through a telescope – unless that is, you give it the time it needs.

Naked Eye

Mars is currently rising at about 20.30 BST. I wouldn’t recommend trying to observe it until about 22.30 though, because it suffers from atmospheric disturbance. If you’re just aiming to find it by eye then its currently in the constellation of Virgo – you find it by following the handle of the Plough down to Arcturus then carrying on to another bright blue star called Spica. Mars is pretty close to Spica in the sky and a similar brightness to Arcturus – in fact the two are easy to mistake. The difference is that Mars, as a planet, won’t twinkle and will appear slightly more orange.

Image thanks to Stellarium

Binoculars

Through binoculars there isn’t an awful lot to see. It will appear as a small orange disc. This opposition is rather unfavourable so the planet will only show about a 15’’ disc and will appear very unspectacular. Still, this is where the aliens came from in War of the Worlds, during an opposition, so if you think you see cannon-fire on the surface, avoid Woking.

Telescope

Through a telescope the view is… craptastic is probably the best word. To see anything you have to ramp up the magnification something chronic – x200 is the usual recommended minimum and that happens to be around the average limit of seeing from UK skies. My ST80 is limited to about x80 with the equipment I have, so I may as well use my binoculars. I now have a 6’’ Dob (The trolley Dob!) which will give me up to x300, although even at x150 I can see a few of the planet’s secrets. Probably the easiest feature to see is the Southern Polar Cap which is angled towards us at present. You should also be able to get dark patches on the surface – the largest of these is called Syrtis Major. If the seeing is stable, make sure you spend a bit of time at the eyepiece with Mars because it takes a bit of time and effort to see anything. Of course when you do, that feeling of achievement is all the better!

That’s your lot for this time. I promise not to leave it so long until the next one…

Double Stars - Mizar and Alcor

At the time of writing, there’s a bright moon in the sky. As a rule of thumb, if the moon's up then it's the only thing worth looking at. But I’m not looking the moon this month, I’m saving that up. Instead we’re going to take a closer look at a star we used last week in our search for Polaris.

Naked Eye

Take a second look at the Plough. The middle star of the “Handle” is the one we’re interested in.

It doesn’t take a dark moonless night to see that we’re not looking at one star here, we’re actually looking at two. Mizar and Alcor are, perhaps, the most famous double star in the sky. In reality they’re quite far apart and don’t orbit each other. In fact all but two stars in the Plough are moving in the same direction in space, suggesting that they are all related. This is unusual for a constellation, but the Plough isn’t a constellation, it’s an asterism, a grouping within a constellation. If you look around the area of the Plough, most nights you’ll be able to pick out the rest of Ursa Major, the Great Bear.

Unusually it pretty closely resembles what it’s supposed to depict – you can see the legs, the head, the snout and… the tail. Yes, the Great Bear has a great big long tail, which doesn’t make a lot of sense, but nearby in the sky is a constellation called Lynx that most certainly doesn’t look in any way, shape or form, cat-like. So a long-tailed bear is pretty close in astronomical terms.

Binoculars

Through binoculars there are, quite clearly, two stars. The ancients used it as a test of eye-sight. Through the bins you may be able to see a third star in between the two. It was named Sidus Ludoviciana after a German nobleman and was originally thought to be a planet. In the end it turned out to be a star in the same line of sight, but much further away. To see a proper binary system here, you need a telescope.

Telescope

With the greater magnification that a ‘scope brings, you can finally reveal the secrets of Mizar. In fact this bright star is a double with the two stars very close together (14 arc seconds). Each component of Mizar is itself double making the star a quadruple system. Because of the proximity of each pair, the only way to tell they’re double is by looking closely at the light produced by the stars – the science of spectroscopy. It transpires that double stars are quite common in the universe and our own sun is unusual for being on its own.

Next time it’s going to get even more exciting because we’re going to be making babies. Baby stars that is…