So you think the clouds got the best of your plans to view that huge new sunspot group? Fear not for SOHO is on the job. The Solar and Heliospheric Observatory has been one of the most productive space astronomy missions ever launched.
Figure 6.3. A LASCO C3 image from the SOHO spacecraft. NASA image.
Despite running into several problems, including a loss of communication and orientation that nearly caused the loss of the mission, SOHO on a continuous basis beams back pictures of the Sun through its many different cameras.
SOHO carries 12 instruments on board to study the Sun's entire structure. Throughout each day, the SOHO web site updates eight images of the Sun. Four images are taken from Extreme Ultraviolet Imaging Telescope (EIT) at varying ultraviolet wavelengths. The various images show the movements of gas at several different levels of the Sun. The hotter the gasses, the higher you are looking in the solar atmosphere. At 304 angstroms, the brightest gas is about 60,000 to 80,000 degrees Kelvin. The 284-angstrom images are the hottest gasses at over 200 million degrees!
There are two images taken by SOHO's Large Angle and Spectrometric Coron-agraph (LASCO). The images taken by the wide-angle C3 imager are the ones that have produced the most unexpected scientific rewards when it began picking up Sun grazing comets! Astonished astronomers have just found as of this writing their 1,000th comet using SOHO. SOHO also uses a narrow-angle instrument called the C2, which images the inner solar corona out to about five million miles of the Sun's surface.
The last two images are taken by the Michelson Doppler Imager (MDI), which images the Sun across the entire continuum and is close to what the Sun looks like in visible light. The magnetogram highlights areas of powerful magnetic activity.
Our Sun is the dynamo that drives all life here on Earth. Light and heat radiate from it to illuminate and warm our world. Yet in the grand scheme of things our Sun is quite normal, a very average star in terms of energy output, luminosity, size and temperature. It is the very model of an ordinary hydrogen fusing star, rock steady in its output and unchanged for billions of years. We take it so for granted and yet it means everything to us. It affects our lives in subtle ways as well. By blinding our communications satellites in a fit of temper, it can affect services that are a given part of our daily lives. By learning more about it and how to predict and understand its more violent tendencies, we can better learn to prepare our technology and ourselves for those times when the Sun is not so even-tempered.
Mercury, Venus, ann trip Tnnpr
- Solar System
Figure 7.1. Venus at greatest brilliancy on May 14, 2004. Image by author using a Celestron Super C8 Plus and a low-resolution video eyepiece.
Every object in the heavens conveniently passes opposite the Sun in the sky and makes it very easy for us to see them except for two. These two enigmatic objects make it very difficult for observers to see and enjoy because they rarely if ever wander far from the Sun. Instead they stray east of the Sun coming into view for a few short weeks or months,hugging the horizon murk, then they dart back towards the Sun disappearing in front of it, then emerge west of the Sun into the predawn skies, playing the same tantalizing games of hide and seek before sunrise before circling behind the Sun gradually sinking out of view. The planets Mercury and Venus have therefore hidden their secrets from us more effectively than any other objects in the solar system. Because they always hide low in the twilight murk, the seeing through a telescope is always poor, leaving the tiny disks of the planets swarming in the turbulent atmosphere close to the horizon. Yet with work and patience, Venus and Mercury slowly yield their secrets and visual treats to the patient amateur astronomer. Both planets require more careful planning to observe than do the other planets or nighttime objects. When the outer planets are at their best and brightest, they are visible all night, so you can set up outside about anytime you want. The inner planets may only offer you an opportunity that is just a few minutes long. One must plan wisely and know what you're going to do long before you actually observe. One must also realize that the rules for observing Venus and those for observing Mercury turn out to be very different from each other.
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