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Blog : Post Category : Astronomy : Page 2

The stag cry and the slaughter

Or, the turning of the year

A few weeks ago, I read on Twitter—sadly I seem to have lost the reference—that the Welsh Hydref, used for either the month of October or autumn as a whole, originally had the literal meaning of “stag-cry”. From that, it turned into “stag-rutting season” and hence autumn. Geiriadur Prifysgol Cymru lists “stag-rutting”, but not “stag-cry”.

Moreover, November, mis Tachwedd, literally means “the month of slaughter”. Together, I think they make a beautifully evocative phrase. The stag-cry and the slaughter. Winter is setting in.

I spent a while sitting outside on clear nights over the past week, hoping to see the Geminid meteor shower. Nothing much, sadly, came of it. On Saturday, though, I did see a handful of meteors in the night sky. I’ve always looked for summer meteors before, flashing across the sky in a razor-thin line; but these were relatively slow-moving, fat things. I say “slow-moving”: they still crossed my field of view in little more than an instant. Their light was a much broader line, though, tapering at start and finish. If nothing else, it gave me good inspiration for the story I posted yesterday. Hopefully I’ll have better luck when the Geminids come around again next year. This year, though, is now nearly at an end. The stag-cry and the slaughter, and winter is upon us again.

Astronomy news of the week

Or, how to spot a shooting star or two

This is not going to turn into an astronomy blog, I promise, and I know I already mentioned some exciting upcoming astronomy news just over a week ago. There is something else interesting and astronomical happening in December, though.

In the meantime, the clouds did briefly break on Saturday evening to give us our first chance of using The Child Who Likes Space’s telescope without the moon shining bright in the south. We had a look at Mars, and then I successfully found Uranus, navigating downwards from Sheratan, the nearest naked-eye star I could easily pick out; it’s currently near to the boundary between Aries and Cetus. Looking just like another blue star, I would have had no idea, without guiding myself with a map on the computer, that we were looking at a planet instead.

And then, naturally, I started sending messages to people saying “Guess what? I’ve been spying on Uranus”, because I still have the sophisticated sense of humour of a ten-year-old.

The exciting event that’s coming up in a week or so’s time is: the Geminid meteor shower. I say “coming up”: it’s expected to be at its strongest at around 2 in the morning next Monday (the 14th), but if it is a strong shower this year, there should be activity visible for a few hours either side of that time, and even for a few days. Incidentally, because of the geometry of how meteor showers work—they happen when the Earth passes through the trail of dust left behind a comet or asteroid—the peak time is the same wherever you are, with the location of the peak moving around the planet as it spins. The Geminids were first noticed in the 1860s, but their “parent”, the asteroid 3200 Phaethon, was not discovered until 120 years or so later.

I’m not sure I’m going to risk keeping The Child Who Likes Space up until midnight to watch for meteors, much as I’m sure he would like to. If the skies are clear late one night this week, though, I might try wrapping up warmly and setting up my deckchair in the garden. There’s no point trying to use a telescope or binoculars to spot meteors; all you need is a comfy chair you can lie back in and look up at the sky. Give your eyes half an hour to adapt to the dark, then look up, look around, and wait for them to streak across the sky.

More astronomy news

A significant event is coming up

One last astronomy post for a while, and then I’ll talk about something different, I promise: in a few weeks time, on December 21st Saturn and Jupiter will be at their closest conjunction for several hundred years.

The Plain People Of The Internet: Conwhatnow?

They’ll come close together in the sky. The closest they’ll be for a few hundred years, in fact. They’re already fairly close in the sky right now, but on December 21st they’ll be so close that to some people they’ll look like a single spot of light, although people with 20/20 vision should still be able to see they are two separate dots.

Unfortunately … I’m not sure I’ll be able to see it. They’re both on the far side of the sun from us right now, and we’re basically watching Jupiter passing in front of Saturn from our perspective on the other side of the solar system. Because of this, they’re also fairly close to the sun in the sky, which means you don’t get a very long window of opportunity to see them. They will set together in the south-west sky only about 90 minutes after the sun does, so you have a brief window of time to see them together at dusk. If you’re on a south coast then things are grand; if you’re in a town, they may well be already below your neighbour’s roofline before the sky gets dark enough to see them. Personally, our only chance will be from an upstairs window. Fingers crossed, though, the sky will be clear enough to see something of them both together.

One of our galaxies is missing!

Or, more astronomy for beginners

Yesterday afternoon, sitting at my desk as dusk was falling, the skies were clear and I could clearly see the moon and Mars rising in the sky. As soon as I logged off from work, I scampered downstairs and went outside, and saw Jupiter and Saturn just visible above the rooftops at the back of the house. “Let’s get the telescope!” I said to The Child Who Likes Animals Space. “Before they set!”

“Before what set?” said The Child, but I was already rushing off to get his telescope and set it up in the back garden.

By the time I’d hoicked it out of its box, Jupiter had already gone down below the roofline, but Saturn was still there. Sadly, I could only see it when I was stood up. The telescope, sitting on a camping table, was too low down to spot it. I briefly considered setting the smaller camping table on top of the larger camping table and making some sort of rickety makeshift telescope-tower, but it would probably have ended in some sort of injury to one or both of us. So, like we’d done before, we looked at the moon, we looked at Mars, and we looked at random bright stars. “Point it at that blue thing!” he shouted. “That’s a very hot star!” This time, at least, he was a lot calmer and could stand still looking through the eyepiece without having to break off every couple of seconds to run back and forth with excitement. I experimented with holding my phone camera in front of the eyepiece. Worst. Astrophotography. Ever.

Worst. Astrophotography. Ever.

After The Children decided they’d rather go inside and watch TV I left the telescope set up; and after they’d gone to bed, the skies were still clear. Time for some telescope practice for me, I decided. Using an app on my phone to show me roughly where things were, I tried focusing on key visible stars then swinging the telescope sideways to find a nearby Messier object. The results? Not very successful, other than a possible sighting of M29, the Cooling Tower Cluster.

Getting a rough fix and vaguely hoping to spot the thing clearly wasn’t working. So, I fetched my laptop, and fired up Stellarium in Night Mode. I picked a target—the Triangulum Galaxy—and went looking for it.

Although the skies were clear, the seeing wasn’t great. Even a newbie like me could tell that the seeing wasn’t good. Vega normally stands out to me like a sore thumb, but last night it didn’t really appear any brighter or more significant than the stars of the Northern Cross to its south, which normally are noticably fainter. Nevertheless, I could see Hamal and Sheratan, the brightest stars in Aries, and could spot the telescope nicely onto Hamal and swing it between the two. Zooming in on Hamal in Stellarium, and flicking my head back and forth from the telescope eyepiece to the dim red screen of the computer, I could slowly navigate my way upwards from star to star until I reached Mothallah, which I hadn’t managed to see with the naked eye.

Road map of the stars

From there, I could similarly hop south towards the spot where the Triangulum Galaxy should be, navigating from star to star and matching the scene in the sky to the screen of the computer. But when I reached it: nothing. Just a blank patch of sky. I found Mothallah again, then worked my way across by a different route. Still nothing. The Triangulum Galaxy has been stolen!

Let’s try the Andromeda Galaxy instead, I thought, given that it’s one of the brightest galaxies in the sky. I found Mirach by eye, spotted the telescope on to it, and walked over to where the galaxy should be. Another blank patch of sky, with a faint hazy blob in the middle of it. Hurrah! A faint hazy blob!

I’m almost glad I hadn’t found it the other day when The Child Who Likes Animals had asked me to find it, because I suspect if I had he’d have been awfully disappointed. I was a bit puzzled, though, because in theory the Andromeda Galaxy is of naked-eye magnitude. I should have seen much more than a fuzzy blob, surely?

A quick note about how astronomical “apparent magnitude”, or brightness to you and me, works. It’s a relative scale based loosely on the subjective scales used by ancient astronomers, and as it’s relative it’s written down as a number without units. The higher the number, the fainter the thing is; and a difference of five in the apparent magnitude number means “a hundred times brighter”. If you have a calculator to hand you can work out that a drop in magnitude of 1 therefore means “2.5119 times brighter”.* The star Vega, mentioned earlier, has magnitude 0, so a few things in the sky have negative magnitudes: Sirius is -1.47, Jupiter varies from -1.66 to -2.94, and Venus from -2.98 to -4.92, almost 100 times as bright as Vega.

On a good night, with a clear dark sky, the human eye should in theory be able to see things as faint as magnitude 6 or so. Last night was clearly nowhere near that: I could see Sheratan at 2.655 and Albeiro (in the Northern Cross of Cygnus) at 3, but couldn’t see Mothallah at 3.42. Through the telescope, though, I was happily stepping my way across the sky using stars of 8 to 8.4, roughly speaking, stars around 140 times less bright than the faintest I could see without it.

The Triangulum galaxy, though, is officially** of magnitude 5.72. Andromeda is considerably brighter still, around the same magnitude as Mothallah. So what was going on?

A galaxy isn’t a point of light, like nearly all stars are. Nearly every star in the sky, other than a handful of stars like Betelgeuse when seen through very high magnifications, appears to be just a single point of light to the viewer here on Earth. A galaxy, by comparison, covers a broad chunk of the sky. That small fuzzy blob I could make out in Andromeda was really just the very brightest core of the galaxy; and the rest of that 3.4 magnitude of light is spread out over an area wide enough to fill my entire eyepiece. Through the telescope, it just becomes a vaguely paler area of sky.

Hopefully at some point we will get the telescope out on a night with rather better viewing conditions, and be able to see all of these things properly. Until then, it seems strangely unintuitive to be able to see hundreds of dimmer stars but not a theoretically many-times-brighter galaxy. That, though, is just how the physics works.

* Apparently, the formal definition “five means a factor of 100” was set down by a Victorian astronomer with what I think is a great name, N R Pogson. The relationship 1:2.5119 is therefore known as Pogson’s Ratio.

** I say “officially”. I mean “according to what I’ve just read on Wikipedia”, of course.

Astronomy

The art of not seeing very much (as yet)

The other day I mentioned The Children have just turned seven. As The Child Who Likes Animals has spent quite a lot of time in recent months liking space instead, watching Brian Cox’s The Planets innumerable times, memorising lists of dwarf planets, Kuiper Belt objects, centaurs and so on, and learning the difference between a red dwarf, a white dwarf and a brown dwarf. We decided, therefore, that it might be a nice idea for The Mother to get him a telescope, as a suitably grandmothery sort of present. Not trusting The Mother to judge what might be suitable, I reached out to a few astronomers I know for recommendations, and found something that both fell into The Mother’s budget and had a reasonable chance of imaging the rings of Saturn. The number of times I’ve looked down a telescope myself before can be counted on the fingers of one hand; but if I was age seven, was given a telescope, and found that it couldn’t show the rings of Saturn I’d be terribly disappointed.

Of course, I messed up to a certain extent. I’m sure I achieved my objectives, but there’s no way really that The Child Who Likes Animals would be able to actually point the telescope at something himself. So, this is going to be the sort of present that I set up in the garden on dark nights; find out what he wants to point it at; try to point it; and then he looks down the eyepiece. Naturally, it becomes a family event, with The Child Who Likes Fairies also wanting to get involved.

As I said, I’ve hardly ever been near a telescope before, despite having books and books on astronomy when I was that age myself. So, on the few nights we’ve had so far when the cloud has at least been broken rather than blanketing, it has gone something like this: I set up the telescope outside. A child asks to point it at something, in a brief pause for breath whilst running around with crazed excitement. If it is an easy thing—the moon, say—I contort myself to the right angle to try to see through the finder, point the telescope and roughly nudge it about until we can see what we’re looking for, all the time with said thing bouncing up and down in the eyepiece as children bounce up and down on the decking. A child then steps up, instinctively grabs the telescope and knocks it out of alignment, and we go back to square one.

Eventually everyone has seen what we’re looking at, and one of them will name something else. I try to work out how to find it, with my laptop and a copy of Stellarium. I fail to find it, and end up sawing the telescope back and forth across the sky desperately trying to find the thing they have asked for. I try again with the finder, drape myself over the telescope and twist it around until the red finder dot is in just the right place; then look through the eyepiece and see nothing but haze. I look up at the sky again, and my target patch of sky, clear a few moments before, is suddenly covered in thick cloud. This cycle repeats a few times, until we either look at the moon again instead, or The Children get bored and go back into the house.

So far, we’ve successfully looked at the moon, Mars, and some random patches of sky that have lots of stars in but nothing I can actually put a name to. Oh well. I’m sure at some point we will get the hang of it, even if I end up becoming the main telescope user myself. It certainly has shown me just how non-empty an empty-looking patch of sky actually is, even living in a hazy, foggy, light-polluted city like this one. I’ll let you know if I manage to find anything less easy to spot. Or, indeed, if we do ever see the rings of Saturn.