Saturday 28 May 2016

Don't forget the sun!

Most people believe that you can only do astronomy at night and preferably in a remote place where the stars still form a sparkling blanket in the sky. Hence the rather awkward reputation that many astronomy enthusiasts enjoy. But that couldn't be further from the truth! 

Studying and analising the stars is extremely difficult because they're so mind-bogglingly distant. To give you an idea of what I'm talking about, imagine that the Earth's the size of a peanut. In that case the nearest star would be... 20.000 miles away! So if we want to study the physics and dynamics of a star, why would we go through all that trouble of studying such remote objects when we've got a very nice example threehundred thousand times closer to us? As you all know, the Sun is a star. Not a particularly bright one and certainly not a very big one I might add, but yet a very stable, middle-aged example. So if we understand our Sun, we can also understand other stars, even those that reside in the most distant galaxies. Therefore the observation of our Sun is a very important part of modern-day astronomy and also many amateurs have special equipment to observe our star in a safe way. Please, do not observe the sun with the unprotected eye! The story about Galileo losing his sight after having observed the sun is nothing but a hoax and in reality he became blind of cataracts. But if I were you I wouldn't try to find out what the sun looks like through an unfiltered telescope which can concentrate sunlight a thousandfold! However, there are plenty of methods and instruments out there which allow you to observe the sun in all safety. Unfortunately I haven't got them. But today I'd like to share the work of a friend who has.

Iain is a British astronomer with decades of experience and just like me he's a keen sketcher. In fact, I often see him as a source of inspiration so I regard it an honour when he allowed me to post his work here. Recently Iain published a 60-frame animation of 6 different sketches showing a spectacular solar prominence. A prominence is an ejection of gas from the sun's atmosphere, often loop-shaped and reaching hundreds of thousands of miles into space. Indeed, the Earth would look tiny in respect! The process that generates them still isn't completely understood but usually they form within a day's time and they may persist for weeks or even months. The animation shows the changes of the prominence in the period of one day:

I'd also like to invite you to visit Iain's stunning blog on which you can also find some amazing solar photographs and photo animations he made, apart from his beautiful deep-sky work:


And now I'll be gone for a couple of weeks because... I'm getting married next Friday. :-) But don't worry... I'll be back!

Thursday 19 May 2016

The wealthy charioteer

Auriga is a very rich constellation because the Milky Way runs through it and therefore it houses many star clusters and nebulas. Although it's interesting to note that it lies exactly on the opposite side of the centre of our galaxy! Its Latin name means "charioteer" as it is often identified with the legendary Athenian hero Erichtonios, who was credited with the invention of the four-horse chariot. 

When you take your binoculars and point it at Auriga, you'll easily notice why even ordinary field binos make a perfect instrument for observing the night's sky. Here's a combination of three views through my 100mm binoculars, showing you three of the most famous star clusters: M37 (on the left), M36 (centre) and M38 (on the right). I already posted a zoomed-in sketch of M37 here which was made with my old 18" telescope, so now you can make a comparison between a telescope and binoculars. As you can see, both instruments are perfectly complementary because they're doing a different job: the binos offer a wide field of view and allow you to travel across the heavens, whereas the telescope zooms in on a particular object and shows you the smallest details. 

As you'll remember, M37 is already a fairly old star cluster, with an estimated age between 400 and 550 million years, and yet it is extraordinarily rich with over 500 identified members. Usually star clusters break up as they grow older, torn apart as they are by the tidal forces of our galaxy, and the stars each go their own way. But M37 on the other hand has remained extremely compact, probably because it's such a large and compact cluster and the gravitational pull of the group is strong enough to counter the pull from our galaxy.

M36 is much younger than its neighbour, estimated 25 million years, and it contains a lot less stars as well - about 60. But due to its young age the stars are still much hotter and therefore this smaller cluster, even though it lies at roughly the same distance (4.100 lightyears), looks slightly brighter to us. If it were closer, it would actually very much resemble the famous Pleiades

And then there's M38. As far as age is concerned, it lies exactly between the other two: 220 million years. It contains twice the number of stars of M36 but here our galaxy's gravitational influence is evident and it's structure has become very irregular. Most observers describe it as an oblique cross, rather than it having a standard circular shape. With time it will dissipate ever more until the cluster will be gone completely.

But this isn't all! If you look carefully, the three have yet another companion, albeit a much smaller one, denominated NGC1907. It lies just a tad to the bottom-left of M38... can you spot it? This little cluster contains only 30 members because most of its stars have already gone their own way. It's about the same age as M37 so here you see what usually happens to older star clusters. Scientists have also measured some interaction with nearby M38, although they were born in different regions of our galaxy and obviously have a different age as well. So probably we'll have to conclude that the pair are just having a coincidental fly-by. 

Wednesday 11 May 2016

Mirach's Ghost

Mirach is the brightest star in the constellation of Andromeda. It has a deep red colour indicating that it's cooled down significantly as it expanded to a size roughly 100 times our Sun towards the end of its life. Its colour is so stable that it has served as one of the references for stellar classification. Apart from this, you wouldn't expect anything particular about it. It's just an old giant star without any characteristics that would make it worthwhile dedicating a sketch to it. Well, at first sight anyway.

But hoho... Wait a minute! What's that faint patch on the right of the field of view? Yes, that's right! It's a galaxy! It's not all that easy to see because bright Mirach is slightly blinding you and that's why they nicknamed it "Mirach's Ghost". Now you see it, now you don't. But when you let your eyes adjust to the field of view it will certainly leap out at you, even through not very large telescopes. 

NGC404, its scientific name, is a dwarf galaxy at the reasonably close distance of 10 million lightyears. Yet, it is classified as a so-called "field galaxy" because it doesn't seem to have any gravitational interaction with other galaxies, even though it's quite near to our local group. The poor little thing just lies there, completely isolated and very inactive. Like other early-type galaxies such as M105, there's very little star formation going on and it appears to be slowly dying. Scientists believe that at some point it had a spiral structure and hence was very active but that a dramatic merger with a companion, some 1 billion years ago, reduced it to its almost vegetative state. Very few details can be discerned and especially through amateur telescopes you shouldn't expect to see more than a blurry little patch. Analysis revealed however that it has a pair of haloes of neutral hydrogen and that it houses a massive black hole too. 

So all in all, the combination of two seemingly uninteresting objects, Mirach and NGC404, still make a wonderful observation. Especially since both the star and the galaxy have a lot in common: both have reached the end of their life and both display very little activity. Astronomy isn't always about spectacles, cataclysms and dazzling star fields. Sometimes, something very simple can prove to be a beautiful tableau.