Posts Tagged ‘opposition’

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)



Mars at Opposition 2014

This week the red planet Mars reached opposition, making it best placed for observing. Opposition is, as the name suggests, the point where a planet is directly opposite the Sun in our sky.

This means that Mars is up all night long at the moment, rising as the Sun sets and setting as the Sun rises, and so you should be able to spot it whatever time of night you’re out.

Mars reached opposition on 8 April, but on 14 April it will reach its closest approach to Earth, at a mere 57.4 million miles!

On that night – and on nights near that date – the planet Mars will shine very brightly at magnitude -1.5, brighter than anything else in the night sky except the Moon (which is Full on 14 April, and sits near Mars) and Jupiter.

Mars in the sky at midnight on 9 April

Mars in the sky at midnight on 9 April

Mars also looms larger than normal when seen through a telescope, at a whopping 15″ (15 arcseconds = 0.25 arcminutes = 1/240 of a degree!). Stargazers with a decent sized telescope, good observing skills, and good observing conditions should be able to make out the north polar cap of Mars which is tilted towards us at the moment.

Through a small scope you might catch it looking like this:

Mars as seen through a small telescope

Mars as seen through a small telescope

Uranus at Opposition 2013

October 3, 2013 Leave a comment

The gas giant planet Uranus, the seventh planet in our solar system, reaches opposition today at 1558 BST (1458 UT), meaning that this is the best time of the year to find this elusive planet.

Opposition is the name astronomers give to the point at which a planet is directly opposite the Sun in the sky. This means that the planet rises as the sun sets, gets to its highest in the sky at midnight, and sets again when the sun rises, meaning that it’s in the sky all night long.

The exact instant of Uranus’ opposition this year occurs on 3 October at 1458 UT, but Uranus moves so slowly against the background stars that there will be ideal observing conditions all month long.

Uranus was the first planet to be discovered after the invention of the telescope. It was first seen in 1781 by Sir William Herschel. The reason it hadn’t been seen before was that it is not a naked eye planet… But actually it is. At opposition tonight Uranus shines at magnitude 5.8, which is right at the edge of what’s possible to see with the naked eye. You’ll need really dark skies to see it, and perfect eyesight too, but even if you can spot it without a telescope it will only look like an incredibly dim star. Through a telescope you might make out a tiny blue-green disk, only 10% the diameter of the much nearer and much larger Jupiter.

To find Uranus look for the constellation of Pisces high in the south at midnight UT, or 1am BST. Uranus rise to between 30° and 40° above the horizon, depending on your viewing location in the UK. Here’s a handy finder chart (courtesy of Stellarium):

Screen Shot 2013-10-03 at 13.57.54


August Asteroids: 3 Juno and 7 Iris at Opposition

August 3, 2013 Leave a comment

This month two of the brightest asteroids, 3 Juno and 7 Iris, will be at opposition in our skies, giving a great opportunity for asteroid hunters to track down these lumps of space rock.

Bear in mind though that you (almost certainly) won’t be able to see them with the naked eye, and that you’ll need binoculars on a tripod or a telescope to find them properly. And even then they’ll just look like very faint stars. But they’re not stars; they’re asteroids, lumps of rock in our solar system orbiting the Sun between Mars and Jupiter.

How big and bright are they?

3 Juno and 7 Iris are amongst the largest of the asteroids, a few hundred kilometres along any one axis. This might seem pretty big but they’re tiny compared to the planets, and so don’t reflect nearly as much light back to us, and are therefore much fainter.

Their magnitudes vary depending on how far away they are from us. They both vary between around seventh and eleventh mag; at their brightest 3 Juno is magnitude 7.4 and 7 Iris is magnitude 6.7. This only occurs under perfect conditions, and this year’s oppositions for both asteroids won’t have them presenting their very brightest aspect. The generally-accepted view is that the human eye can only see down to magnitude 6, but in exceptional circumstances – very dark skies free from light pollution, and very good atmospheric conditions – and with exceptional eyesight, you might just be able to see 7 Iris when it’s closest to us, and at its brightest.

When can I see them?

They’re visible all month but the best time to look at them is when they’re at opposition. That means they’re directly opposite the Sun in the sky, and therefore rise as the Sun sets and set as the Sun rises, getting to their highest due south around midnight.

3 Juno reaches opposition on Sunday 4 August 2013 and it’ll brighten up to magnitude 9. You’ll need a scope, a good star map, and patience to track it down.

7 Iris reaches opposition on Friday 16 August 2013, and it’ll be brighter than 3 Juno, but still not near its best, gaining magnitude 8 during this year’s opposition. Again, a good star chart and telescope is needed.

Where can I see them?

They are both visible in the lower part of the southern sky in the constellation of Aquarius, but you’ll need very detailed star maps to help you find them. 7 Iris is only a degree or so away from the brightest star in Aquarius, β Aquarii, on the night of opposition, making it a bit easier to find. The British Astronomical Association computing section has downloadable star-charts to help you find these asteroids, and others.

How will I know that I’m looking at an asteroid?

The short answer is: you won’t, at least not at first. Asteroids, even the brighter ones like 3 Juno and 7 Iris, will only ever appear as tiny specks of light when seen through a telescope, just like the millions of other tiny specks of light, the stars. However if you observe them over the course of a number of nights around opposition, and mark their position on a star map, then you’ll notice that their position changes relative to the “fixed” stars, as they circle the Sun and move through space.

Don’t be put off if you don’t manage to find them. While you’re out hunting for them don’t forget you can check out lots of other amazing sights through your telescope. Why not have a go at finding the Ring Nebula in Lyra, high overhead this month.

Good luck, and happy asteroid-hunting!

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