Space Probes And Hubble

As well as observing the planets out of sheer fascination and actually seeing them with your own eyes, the images returned by planetary space probes throughout the last few decades have been truly staggering and are well worth tracking down on the web. While manned spacecraft have only traveled as far as the Moon, unmanned robotic spacecraft have traveled to every planet except Pluto. Traveling at speeds as fast as 60,000 kilometers per hour (17 kilometers per second), these probes still take years to arrive at the most distant planets, Saturn, Uranus, and Neptune, indicating just how large our solar system is and how slow our rockets are for interplanetary travel! We also have the Hubble Space Telescope images of the planets and ground-based images from professional observatories. This might all lead one to think that backyard images of the planets are of little scientific use, but nothing could be further from the truth. Space probes have a limited lifetime and a specific set of tasks to perform. It is very rare for any space probe to constantly monitor the whole surface of a planet in the way that an amateur astronomer (or network of amateur astronomers) can. Likewise, the Hubble space telescope has only maintained an occasional coverage of the planets and mainly when they have been at their best. Strange though it may seem, dedicated networks of amateur astronomers are best placed to study the planets, as even ground-based professional observatories tend to concentrate on imaging the most distant objects. Even today, if a dust storm erupts on Mars or two spots start to merge on Jupiter, it is the amateur astronomers who will be collecting the most images. So from your own backyard you can do real science, if you want to.

Of course, to make any serious observations you really need a decent telescope and, ideally, one of about 200 mm aperture or larger. For webcam work you need a PC and a webcam. The only other thing you need is enthusiasm and this book. I would like to think that there is enough information contained in these pages to really inspire a few people to become serious planetary imagers.

Good luck on your journey, but a word of warning. This hobby can become very addictive: you have been warned!

The opposition dates and sizes of the planets Mars, Jupiter, and Saturn are listed below. These are the best times to view these planets. An outer planet is at opposition when it is directly opposite the Sun in the sky. This occurs when it is closest to the Earth and it is crossing the meridian (i.e., is highest in the sky) at midnight. MARS: 2007 Dec 24; 2010 Jan 29; 2012 Mar 3.

JUPITER: 2006 May 4; 2007 Jun 6; 2008 Jul 9; 2009 Aug 14; 2010 Sep 21; 2011 Oct 29; 2012 Dec 3.

SATURN: 2006 Jan 27; 2007 Feb 10; 2008 Feb 24; 2009 Mar 8; 2010 Mar 22; 2011 Apr 4; 2012 Apr 15.

CHAPTER TWO

Webcams, Plus a "Quick Start" Guide

This book is about observing the Moon and planets using webcams, those small, cheap little cameras that plug into your PC for live video messaging. If you are comfortable with PCs, software, and telescopes and want to get started imaging now, read the Quick Start Guide at the end of this section first. However, if you are less confident with imaging technology, but maybe fairly knowledgeable about telescopes, you will need to read on a bit further and, at some point, jump to the full webcam beginner's guide in Chapter 7. If you are new to astronomy and imaging, just read the book from start to finish!

To the complete novice, the low-tech webcam approach may well sound crazy. Or you may think I am just advocating astronomy on the cheap, for those with the tightest budgets. After all, there are plenty of expensive astronomical CCD cameras for sale: surely these are better? Well, from a mountaintop observatory enjoying perfectly stable air this might possibly be the case, but, in all other instances, the webcam rules supreme. In the century before digital imaging came along, the visual planetary observer with a quality telescope could see far, far more than the photographer could ever capture, even with huge professional telescopes and the sensitive emulsions of the 1980s and 90s. The reason for this was the Earth's turbulent atmosphere. When you look through a telescope at the Moon or planets they are invariably shimmering and distorting as if submerged in a bowl of water. This is the result of the light from the planet having to pass through the Earth's atmosphere. What a tragedy! For millions or hundreds of millions of miles the light from these planets has hurtled toward the Earth in good shape and then, in the last 30 kilometers, it is distorted by the swirling, turbulent air of our planet. It is like having a 10-meter-deep column of swirling water on top of your pristine telescope mirror! From a time perspective, the light has traveled from distant Saturn for more than one hour to get to the Earth and yet it is distorted only in the last 100 microseconds. Look through any decent-sized telescope at high magnification on a typical night and you can instantly see the advantage webcams possess. The atmosphere blurs, distorts, and ripples the planetary image, but, now and again, there is a fleeting moment of calm, when the atmosphere lets the light pass through to your telescope with little distortion. The eye can spot these good moments because it is imaging all of the time. When that good moment occurs, the observer spots it and the skilled planetary artist makes notes and draws a sketch, based on the best glimpses over many minutes of observing. That is how the keen-sighted planetary observer, with patience and a flair for drawing, worked for centuries. In the last century, a few photographs, or even a few CCD images, would rarely freeze the good moments. Indeed, a few snapshots will not let you even focus a normal CCD camera. Is the image blurred because it is out of focus or because the atmosphere is blurring it? It's impossible to tell. With a webcam like the Philips ToUcam Pro (see Figure 2.1) you can focus in real time, just like looking visually through an eyepiece.

Webcams may be inexpensive, but they have a huge technological advantage. The download speed is blisteringly fast. Even with the original USB 1 standard, the cheapest webcams can transfer 30 frames per second to your PC. This is more than enough to focus with and more than enough to outperform the human eye. However, even a webcam has limitations and we will examine these signal-to-noise considerations in more detail later. If you are still not convinced that a humble webcam, linked to a telescope, can achieve better results than any other detector, then just look at the pictures in this book. As a start, look at Figures 2.2 and 2.3. These are raw and processed webcam stacks taken by planetary imaging master Damian Peach with a 280-mm aperture Celestron telescope costing under $2,000. The final image could almost be mistaken for a Hubble space telescope

Figure 2.1. The Philips ToUcam Pro II, model PCVC 840K.
Figure 2.2. A raw stack of 600 webcam frames of Jupiter, taken by Damian Peach, with a Celestron 11 in Tenerife, Canary Islands.
Figure 2.3. The same image shown in Figure 2.2 has been expertly processed by Damian Peach, using techniques explained later in this book.

image, a telescope costing a billion dollars! The way I look at it is as follows: the webcam is the closest thing that technology has produced to the human eye. It captures images fast and is very light sensitive. Only years of research and development by CCD manufacturers like Sony and electronics manufacturers like Philips could produce such a superb, lightweight, quantum efficient, and inexpensive detector like the Philips ToUcam Pro webcam. In fact, the accumulated research has cost multi-millions of dollars, despite your own webcam costing $100 or less. The only downside to a webcam, compared to a custom CCD camera, is that the CCD chip is not cooled, so long exposures (even if the hardware and software allowed it) would be horribly noisy. However, the Moon and planets are bright objects and long exposures are not needed. We want short exposures to freeze the turbulence of our atmosphere and, in this regard, the webcam rules supreme. Suddenly, we can all get good pictures of the planets, even if we have no artistic ability and lousy eyesight!

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