Title: Beginner’s Guide to Observing Jupiter
Podcaster: Martin Ratcliffe
Description: Today’s topic is observing Jupiter with a telescope. And if your telescope is the Hubble, this podcast isn’t for you (newbies only!) And as a bonus, you’ll get to spot Neptune too.
Bio: Martin Ratcliffe received his BSc in Astronomy from the University College London, England. Martin has published 4 books, including The Night Sky Revealed (Barnes and Noble) and State of the Universe 2008 (Praxis-Springer). Although his final year research project was published, he pursued a career in Planetariums, working at theaters in Armagh, Northern Ireland, Buhl Planetarium in Pittsburgh and the CyberDome Theater in Wichita, Kansas. A former President of the International Planetarium Society, Martin is a contributing Editor for Astronomy magazine, co-writing the Sky Show monthly column for the past 13 years. He is now Director of Professional Development for Sky-Skan, a leading digital planetarium manufacturer.
Today’s sponsor: This episode of 365 Days of Astronomy is sponsored by Clockwork.
Hi my name is Martin Ratcliffe, hailing originally from England and now resident for the past twenty years in the US working in planetariums, and in my spare time I write for Astronomy magazine. Today’s topic is observing Jupiter with a telescope. And as a bonus, you’ll get to spot Neptune too. Don’t forget to read the Sky-Show column each month in Astronomy magazine for the current visible planets, what to see and where to look.
Before I disappoint anyone upfront, if you’re listening to this and you’ve used Hubble for your planet observing, this podcast is not for you. Today I’m going to focus, forgive the pun, on “newbies,” those who are new to astronomy, and are wondering what you can see through your telescopes. In this podcast you’ll hopefully pick up some hints that take you beyond viewing, and move into really observing what you see, because only then will you see the kind of details in Jupiter’s atmosphere that experienced observers see.
Jupiter is the largest planet in the solar system. Everything about the planet is huge. For example, you could fit twelve Earth’s across its equator. While our Earth rotates once in 24 hours, Jupiter takes less than 10 hours. Less than ten hours. Think about that. The equator of the Earth moves at a thousand miles an hour. The equator of Jupiter, ten times greater than Earth’s, spins in less than half the time. It’s equatorial velocity is 28,000 miles an hour.
If you think that’s wild, there’s more. Jupiter doesn’t rotate as a solid object. Its bulk is gaseous, not like Earth’s solid rock. What we see as Jupiter’s surface is really its atmosphere. The equatorial zone region rotates in 9 hours 50 minutes. The rest of the planet, at higher latitudes, rotates in 9 hours 55 minutes. This five minute difference generates huge atmospheric effects along the boundary between the two zones, which is essentially marked by the two dark equatorial belts visible in small telescopes.
Jupiter’s dark belts and bright zones run parallel to its equator. Recall that on Earth, the trade winds blow at an angle to our equator. If Earth did not rotate, these winds would blow from equator straight to the pole – a result of the sun heating the air at the equator, causing it to rise and move pole-wards. It’s Earth’s rotation that skews the winds. Jupiter’s rotation is so fast that all these winds are parallel to the equator, creating belts and zones, regions of high and low clouds that show up as differences in brightness. The strong winds generate a great deal of turbulence, where dark and bright features get mixed up. These create delicate plumes of material, also visible in small telescopes.
So let’s see where Jupiter is in the night sky. It’s going to be visible for the rest of the year, so there’s plenty of time to practice viewing to become an expert.
In June, when this podcast goes online, Jupiter rises at 1 a.m., and is well above the southeastern horizon by 3 a.m. The early mornings are a great time to view any planet, because as we shall hear in a moment, the atmosphere is usually steadier, providing clearer views than in the evening.
Jupiter lies within three degrees of Deneb Algieda, the brightest star in Capricornus. OK, Capricornus is not the easiest of constellations, and Deneb Algieda is nearly 3rd magnitude, not exactly easy to see. And to be honest, if there’s any haziness in the atmosphere, or you live in a city, you won’t get to see this star anyway. Perhaps a better guide is the moon. In the early morning hours of June 13, Jupiter lies to the left of the moon – about eight moon-widths to the left.
So what about the visibility of Jupiter for the rest of the year? Well, if you can imagine in your mind’s eye a 3D model of the solar system and Earth is orbiting the Sun – so is Jupiter, but much more slowly. Currently we are catching up with Jupiter, and by August we have caught up – Jupiter is opposite the Sun in our sky, what astronomers call opposition for the planet. Think about the geometry for a second, and you’ll realize Jupiter will be due south in Earth’s sky at midnight in August, and it rises at sunset. Jupiter will also closest to the Earth at opposition. The two months either side of opposition is the best time to view the planet. By the time Jupiter reaches the evening sky, the best is half over.
So now let’s take a look through a telescope at Jupiter. What can we expect to see? Well for a start, even though Jupiter is a large planet, it lies five times Earth’s distance from the Sun. Even through a telescope it shows up as a small white disk of light at first sight. Your initial view will show the two main belts on Jupiter, because they are dark relative to the rest of the planet.
You might be disappointed with your first glance, but this is where you learn to observe, rather than simply look. Training your eye to see the delicate detail on Jupiter takes time, for two main reasons. First, your eye is not used to looking through a telescope, and it takes a few seconds for your eye to adjust to the view.
In addition, your eye has different regions of sensitivity. The central region of the retina, the light sensitive tissue at the back of the eyeball, is sensitive to color and can detect fine detail. The outer part of the retina simply sees motion and is sensitive to shades of black and white. By moving your eye to different parts of the image, and letting it settle for 10 seconds at a time, you’ll find the best direction to look so you see more detail on Jupiter.
Many of Jupiter’s most interesting atmospheric features are quite subtle, low contrast, and require patient viewing to see.
Secondly, remember you are looking through Earth’s atmosphere. It’s a turbulent thing. Try looking at a friend’s face on the edge of a swimming pool while you are underwater. The water messes with the light path, causing your friend’s face to wobble like it’s made of jello. Earth’s air does the same thing to the face of Jupiter, or any other object you are looking at. Blobs of warm and cold air alternately wander in front of the planet resulting in a jello Jupiter. Here’s where the real experience of observing comes in.
Wait and watch, relax your eye looking at Jupiter and wait. In fleeting moments, the atmosphere steadies, and you see a clear, perfect view of Jupiter. Within a moment, it’s gone, but your memory grabs at the spectacular detail you’ve just experienced. Now you want more, so you wait longer, and there are more steady moments where you see the giant clouds that have swirled into contorted shapes.
As I mentioned, the two dark belts bisect the planet’s disk, both easily visible in most scopes. These giant atmospheric features are seen as straight lines because we are viewing the planet directly in line with Jupiter’s equator. The boundaries of the belts are zones where a lot of activity takes place. Dark spots and bright clouds circulate, carried by Jupiter’s fast rotation. Careful viewing and recording of features will allow you to notice the change in location of spots within 10 minutes, or perhaps 5 minutes if you are using a scope capable of high magnification. Jupiter’s Great Red Spot is not really red anymore, actually a subtle pink and low contrast – nothing like my first views in the 1970’s when it stuck out like, well, a sore thumb.
Speaking of magnification, for the best views of any planet use low to medium magnification – if your scope is between 2 and 3 inches diameter, use no more than 100 times. With an 8-inch scope, keep it below 250 times. The reason is that higher magnification also magnifies turbulence in Earth’s atmosphere, and reduces the surface brightness of the planet. With features that are already low contrast, high magnification is the last thing you want to use. Refractors have better contrast than reflectors, so if you have a choice, use a refractor.
For more advanced recording of Jupiter – attach a video camera to your scope and record video frames. You’ll capture 30 frames a second and be able to freeze the moments of clear seeing through our atmosphere. What’s more, free software like Registax (http://www.astronomie.be/registax/) allow stacking of these good frames and image processing can produce images of Jupiter far beyond what any regular photograph or sketching at the eyepiece can produce.
In addition to Jupiter’s atmosphere, the four bright Galilean moons orbit Jupiter like clockwork, Io taking 1.77 days for one full orbit, Europa takes 3.55 days, Ganymede takes 7.16 days, and Callisto 16.69 days. Note that Io’s period is exactly half of Europa’s, while Europa’s period is half of Ganymede’s. Such resonant orbital periods are common with multiple satellites around planets.
Our equatorial “side-on” view of Jupiter results in the moons passing in front or behind the planetary disk. If the alignment is just right, the moon’s can occult each other, or their shadows can eclipse other moons. About a dozen or more “mutual satellite events” take place each month this year, although not all are visible from one location. Check popular astronomy magazines for details, but for example, one occurs on July 30. Io occults Europa, beginning at 10:20 p.m. C.D.T., and ends 9 minutes later.
Planet viewing is fun, and with Jupiter, a lot of changes take place. If you are interested in more observing details, I encourage you to contact your local planetary observing association. In the US, this is the Association of Lunar and Planetary Observers. You’ll find them on the internet. http://alpo-astronomy.org/
And while you are looking at Jupiter, don’t forget that Neptune lies within a moon’s width of Jupiter, west during June and east in late July. It’s a half degree north of Jupiter on July 14 – not the 5th magnitude bright star, but the fainter 8th magnitude object slightly farther north. You can see both planets in the same low power telescopic field of view during the first three weeks of July. Neptune appears like a dim bluish star of magnitude +7.8.
Thanks for listening, this is Martin Ratcliffe wishing you good planet viewing. You can find my blog at http://www.stateoftheuniverse.com – it’s in its infancy.
End of podcast:
365 Days of Astronomy
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