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Blog : Posts tagged with ‘Jupiter’

The old gods

The astronomy season is starting again

We’re getting to the time of year now when it’s properly dark before a reasonable bedtime; as opposed to a couple of months ago, when it is still twilight in the deepest part of the night, which around here happens at about quarter past one in summer. August, by comparison, is the time of year when I can go outside at 10pm and see if the sky is clear enough to do a small bit of stargazing before bed. It’s too late to wake up The Child Who Likes Space, who nominally owns the telescope, but nevertheless, I rationalise, I can always tell him about it in the morning.

A while ago, I noticed that according to timeanddate.com’s planet apparent size calculator, Jupiter would have a relatively large disc right now. Right now, in fact, it’s receding from us, but it’s still a relatively chunky 49 arcseconds wide. Still a dot to the naked eye—the Moon is about 36 times bigger in apparent diameter if my rough mental calculations are correct—but big for a sky object, and with the best chance we would have of seeing features on it. Over the past few weeks I’ve noticed that Jupiter and Saturn together, although relatively low in the sky, are very definitely the brightest things in the south-eastern sky when I go to bed. So last night, as the sky was almost clear, I decided to get the telescope out.

Last spring I found it rather hard to get the telescope set up in the new garden, due to the street light that shines directly into it over the garden wall. Back then, though, the garden was a rocky, rubble-strewn wasteland, which didn’t help. Now it’s grassed, and at the moment I can tuck the camping table and the telescope into a relatively shady distant corner; from which both planets were shining bright in the sky. It was as easy as any astronomy I could think of: set up the telescope, point the finder on Jupiter, and as soon as I had focused, I had the planet and the four Galilean moons right in the centre of the eyepiece. All four of the moons were on the same side of the planet last night, Io just visible almost touching the planetary disc, the other three clear and sharp and separate spread out to the east of the planet. Jupiter itself was a fairly uniform cream colour, with a thin, darker, more reddish band visible near its equator. It seemed so sharp and clear, much more clear and bright than a photograph.

After Jupiter, I trained the spotter on Saturn, much smaller in the sky. At first it just seemed to be an oval blob, but I’d knocked the focus off slightly. Tweaking it showed the planet, orange in colour, and its rings. We don’t have anywhere near enough magnification to show the ring divisions, and the rings and the planet seemed to have a fully uniform colour. It’s strange to think that when Stegosaurs were alive and tramping the planet, Saturn probably didn’t have any rings at all. I couldn’t make out any of the planet’s moons, but I know they are much fainter than those of Jupiter, my eyes probably hadn’t had time to fully adapt to the dark, and I didn’t know where to be looking in any case. I wonder how different the history of science would have been, if Jupiter didn’t have four clear bright moons for Galileo to spot easily with his early telescopes.

Incidentally, due to geometry, it’s impossible for the planets orbiting outside Earth to have phases like the Moon does: their discs will always appear from our standpoint to be fully illuminated. This coming winter Venus will be the largest planet in the sky—it peaks at just under 63 arcseconds on January 8th—and it will be interesting to see if around then more than a thin crescent is visible. Assuming the skies are clear, of course.

Cloudy skies

And not much we can do about it

Sadly, I didn’t get to see the Great Conjunction of Jupiter and Saturn, at least not at the closest approach that would have been visible. We had heavy rain here this afternoon; and after sunset the sky was a uniform, undifferentiated cloudy mass with not even the moon visible.

Oh well: we had clear skies last night, at least, and I did see them both, maybe only about 10 minutes or so apart in the sky, just over the horizon after sunset. I tried to take a photo on my phone, but although Jupiter was clearly visible on it, Saturn was only really spottable if you already knew it was there. Maybe it’ll be clear skies tomorrow, when they are parting again.

The solstice has passed too, of course. Politically this country might seem be descending into some sort of nightmarish fimbulvetr right now, but at least the heavens don’t know that.

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.