With Mercury, Venus, Mars, Jupiter and Saturn being very obvious in the mornings at the moment, and with Jupiter, Mars and Saturn in opposition in March, May, and June, respectively, I’ve been thinking about planets a lot lately. For this piece, I thought I’d spend a little time discussing planetary observing.
For serious planetary observing you’ll need a telescope (ideally on a sturdy mount – wobbles and planetary viewing really don’t go together), and fairly high magnifications. Binoculars will let you see the moons of Jupiter (as tiny pinpricks), the squashed shape of Saturn, and the redness of Mars, but they won’t show any planetary detail.
However, even when viewed at 200 times magnification with a fairly large telescope, as the accompanying picture shows, Jupiter and Saturn will still appear pretty small.
Magnification
Before we get into specifics, let’s talk about magnification. First off, you can calculate the magnification of your telescope and eyepiece combinations by dividing the telescope focal length by the eyepiece focal length. A good ‘starter’ scope, such as the Skywatcher Explorer 130 has a focal length of 900mm. The 10mm eyepiece which comes with it as standard will give a magnification of 90 times. A useful rule of thumb as regards the maximum useful magnification a telescope is capable of is to refer to its aperture. The Skywatcher 130 has an aperture of 130mm, and most would regard 130 times magnification as the maximum useful possible with this scope (possible with a 7mm eyepiece). The scope just won’t be capable of resolving any detail at higher magnification (so don’t believe the marketing copy and imagery on the box!). A telescope may be theoretically capable of upwards of 300 times magnification, but it’s unlikely you’d ever get to use it, and the view would be soft, fuzzy, dark and disappointing!
Don’t get despondent if your scope/eyepiece combination isn’t capable of high magnification, though. UK skies rarely permit the use of magnifications above 150 times (light pollution, humidity, atmospheric instability, etc just don’t allow more), so enjoy what you have! In fact, less magnification often yields a sharper (albeit smaller) image, with clearer detail.
Mercury & Venus
For the purposes of observing them, we can group the innermost planets together. Mercury and Venus reveal no detail (though with the latter, you may detect the slightest hint of darker patches in the planet’s clouds at high magnification). At best you’ll only be able to see the ‘phase’ of the planets. I actually find this very exciting. Seeing Venus partially illuminated by the Sun, appearing like a small half or crescent moon, really gives depth and a three-dimensionality to the inner solar system. Anything over 40-50 times magnification will clearly reveal the phase of Venus and Mercury, the latter considerably smaller and less rewarding to view.
Mercury is going to be passing in front of the Sun’s disc on Monday, May the 9th (from approximately lunchtime until early evening). This transit promises to be a spectacular sight, though you will need specialised solar observing equipment to view it (remember: never, ever look directly at the Sun!).
Mars
Mars is currently clearing the eastern horizon at about 2AM, but is probably best viewed from about 4 or 5AM. Usually visible as a small, bright, shimmery, reddish orb, Mars has to be ‘coaxed’ into revealing any detail: try using colour planetary filters, for example, and/or higher magnifications (150-200 times). #25 or #29 Red filters are said to improve views of the Martian polar ice caps and the belts on Jupiter, whilst #80 and #82A Blue filters are said to improve views of Jupiter’s Great Red Spot and otherwise low contrast features on Mars. The extent to which filters are deemed to work is a fairly subjective judgement.
The best times to view Martian detail are when seeing conditions are clear, the planet is high in the sky, and, of course, when it’s closest to the Earth. Mars is at opposition (that means that the Earth is directly between Mars and the Sun) on the 22nd of May this year. Being so close, it’ll appear much bigger than it currently does, so polar ice caps and the dark parches on the surface will, hopefully, be visible. It’s always going to be small, though, so patience, averted vision, filters and a variety of magnifications may all be required to get the best from it.
Jupiter
Jupiter never disappoints, though of course seeing conditions do affect clarity, sharpness and detail. Viewed at magnifications above x100 the two main equatorial bands will be clearly visible, but you’ll need very clear skies to detect any of the other major bands, or, indeed, any of the wonderful swirling detail in them. Probably the best view of Jupiter I ever had was at 100 times magnification with my old Skywatcher 130. Although small, the detail was amazing (it was a uncommonly dark, clear and still night, though!).
Jupiter is currently rising above the eastern horizon by about 9PM, and, being so bright, is easy to find. Magnifications of 50 and above will reveal the equatorial bands, whilst the great red spot and Galilean moon transits are easily observed above 100 times magnification. As with Mars, colour planetary filters can help reveal detail.
Saturn
I don’t know of any stargazers who can’t remember their first glimpse of Saturn; there really is something special about the ringed giant. Currently clearing the south-eastern horizon by about 5AM, magnifications of 50 and above will clearly show the rings, and 100 times magnification will definitely leave a lasting impression. Higher magnifications (in the order of 150-200 times) will reveal the Cassini division in the rings, and, if you’re lucky, subtle cloud banding on the planet itself (seeing conditions permitting). You should also be able to spot some of the planet’s moons.
By the time Saturn’s in opposition in June, the planet will be perfectly positioned: reasonably high in the south, and tilted up to show off the rings to their best … this is a very exciting prospect.
Neptune & Uranus
Both past their best now, Neptune sets early in the evening at the moment, and Uranus is fairly low in the evening western night sky (in the constellation of Pisces). Tricky to spot, Uranus reveals itself as a pale greenish orb at magnifications over x100, and, if you’re very lucky, you may even spot one of the larger satellites.
What’s up?
Besides the planets discussed above there’s the, at first glance, fairly nondescript constellation of Canes Venatici (little more than a couple of stars below and to the right of Ursa Major). By about 10PM, however, it’s currently high enough out of the atmospheric murk to reveal a couple of fantastic galaxies. M63, the Sunflower galaxy is a fairly easy find on a dark and moonless night. 10×50 binoculars will reveal a small, faint smudge, but magnifications of 50 and above will clearly show the galactic shape and possibly some detail.
Although possible in 10×50 binoculars, the Cocoon galaxy, just above Canes Venatici, is an excellent example of an interacting galaxy system, and should be fairly clear with magnifications above 40 or 50.
Clear skies!
Kevin Quinn is an amateur astronomer based in Cerne Abbas, he is the proud owner of a ten-inch reflector, a small refractor, a case of eyepieces, and a couple of pairs of binoculars. He tweets via @CerneAstro, blogs via theastroguy.wordpress.com, and his ebook Demystifying Astronomy – A beginner’s guide to telescopes, eyepieces and accessories for visual astronomy is widely available.
©Kevin Quinn
