Posts Tagged ‘moons’

Saturn at Opposition 2014

April 28, 2014 Leave a comment

On 10 May 2014 the planet Saturn will be at opposition, making it ideally placed for observation. To be honest, though, Saturn will be a feature of our night sky throughout the spring and summer, only vanishing into the twilight glow of sunset in September. However, at opposition Saturn rises when the sun sets and sets when the sun rises, meaning it’s in the sky all night long.

Saturn, image by Kenneth Crawford and Michael A. Mayda

Saturn as it might look through a large telescope, image by Kenneth Crawford and Michael A. Mayda

Saturn looks like a bright star in the east at sunset, shining at magnitude 0, making it a little fainter than the other bright planets up there at the moment, Jupiter (at around magnitude -1.5) and Mars (at around magnitude -1), but still brighter than most other stars in the night sky, shining about as brightly as the star Arcturus.

Saturn is the furthest planet we can see with the naked eye (unless you head somewhere very dark and strain your eyes to catch a glimpse of Uranus), lying around 9 astronomical units from us (approx. 827 million miles). The reason we can see it shining so brightly is that it’s quite reflective (reflecting 47% of the Sun’s light that shines on it) and VERY big.

The disk of Saturn will appear larger (just) than the disk of Mars when seen through a telescope (18.7 arcseconds for Saturn compared to 15 arcseconds for Mars), but its rings stretch further, subtending 44 arcseconds.

Saturn really is the jewel of the solar system. It’s the planet that most people recognise, and I would bet that it ranks pretty high on most people’s bucket lists of “things to see through a telescope”. If you have a ‘scope, or know someone who does, it’s worth taking a look as Saturn arcs overhead this spring and summer.

You’ll also catch a glimpse, if observing with a small telescope, of Saturn’s largest moon Titan, the second largest moon in the solar system, larger the the planet Mercury. Saturn has 62 major moons, and countless smaller ones (the rings after all are made up of billions of pieces of ice and dust, mini-moons) but only Titan is visible through small scopes. To see the next four brightest (Dione, Enceladus, Tethys and Rhea) you’ll need a decent sized scope, say 8″.

Saturn, Mars, and Arcturus make a prominent triangle in the south at midnight, 10/11 May (created using Stellarium)

Saturn, Mars, and Arcturus make a prominent triangle in the south at midnight, 10/11 May (created using Stellarium)



Jupiter Triple-Transit 11-12 October 2013

October 8, 2013 Leave a comment

This post is based on a great article by Bob King on Universe Today, titled “Observing Alert: Rare Triple Transit Of Jupiter’s Moons Happens Friday Night (Oct. 11-12)”. Read that article to get the whole story!

UK stargazers can see a rare triple transit of three of Jupiter’s largest moons in the early hours of this Saturday 12 October 2013.

Every so often one of Jupiter’s largest four moons – the Galilean satellites Io, Europa, Ganymede, and Callisto – passes directly in front of the planet Jupiter casting a shadow which can be seen as a tiny black dot through even a modest telescope. This weekend three out of the four Galilean moons are casting such shadows, and from the UK you can watch the whole thing unfold between 0412 and dawn twilight, which occurs between 0600 and 0630 for most of the UK, depending on where you’re observing from (southern stargazers will have an earlier dawn brightening than their northern counterparts).

Here’s the timetable of events, based on the timings in Bob King’s article:

Saturday 12 October:
0412 BST Callisto begins to cast the first shadow
0424 BST Europa adds a second shadow
0532 BST Io adds the third shadow, and the triple transit will last until the sky brightens.

Jupiter will be high in the south-east at this time, in the constellation of Gemini. You won’t struggle to find it; it will be the brightest thing in the entire sky, shining at magnitude -1.8.

Screen Shot 2013-10-08 at 20.04.00

Location of Jupiter at 0412 on Saturday 12 October, from Stellarium

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