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Gently used may contain ex-library markings possibly has some light highlighting textual notations and or underlining. Text is still easily readable. Patrick Moore s Practical Astronomy Series. Michael E. Maragoudakis, Nikos E. Full text of Profile 76 - Internet Archive. Search the history of over billion web pages on the Internet. Get this from a library! Wearing their graduation caps and gowns, the Class of visited Deasy and Gribbin schools to reminisce about their time as youngsters in the district.

Borgia s primer on Human Vision and the Night Sky provides a solid introduction to how the eye and brain interface with telescopic equipment, light and darkness, and introduces some methods for optimizing your night vision. Budget Astrophotography - Imaging. Download for offline reading, highlight, bookmark or take notes while you read Choosing and Using a Dobsonian Telescope.

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That chapter also covers measuring images and reducing to standard magnitudes. This chapter and Chapter 4 differ from the first edition most of all. New approaches have been developed since the first edition for reducing instrumental magnitudes to a standard system. Bad data makes for bad results.

Getting a period out of the data can be as difficult as squeezing the proverbial blood of out of a turnip. There are many tricks to this process, the most important being to understand how changing just one parameter of a system changes the theoretical lightcurve. When you understand those parameter Targets of Opportunity — Asteroids 5 changes versus effects, matching the theoretical curve to your curve becomes much easier. Something new this time around is a set of data for blue—red pairs from the Hipparcos and Sloan Digitial Sky Catalogs that you can use for first- and second-order extinction and, in some cases, transforms.

Space limitations do not allow charts for these fields, but with the excellent planetarium programs available that should be no obstacle.

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While I believe this book truly is a practical guide to photometry and lightcurve analysis, it is by no means the final word. What a textbook presents as current knowledge can be outdated in less than a year, even a few months. The same problem exists when trying to list targets of lightcurve opportunities. Theories and discoveries regarding asteroids have changed somewhat dramatically since the first edition of the Practical Guide and so some items have been dropped from the original list only to be replaced by others or at least take on a different focus or priority.

Chasing after outbursts in cataclysmic variables or sudden, unexpected behavior in an eclipsing binary can easily occupy your observing schedule. In my case, I work asteroids almost exclusively. Others will split their observing time among asteroids, variables of one type or another, and maybe make an occasional foray into supernovae hunting.

Again, there is no shortage of things to do.

With the data used to make a lightcurve, you can help reveal not only the secrets of the asteroid but also the formation of the solar system. Here are just some of the things that can be done with or learned from asteroid lightcurves. That has changed in recent years with work by such astronomers as Mikko Kaasalainen and Steve Slivan. In order to get the best results, lightcurves must be obtained when the asteroid is at significantly different aspect angles or viewing angles. This is not for just one apparition, i.

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With each apparition, the spin 7 8 Targets of Opportunity — Asteroids axis of the asteroid likely has a different angle from the line of sight to the observer. Imagine looking at a spinning potato with the spin axis at right angles to the line of sight.

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Then imagine how the lightcurve might look. As the potato rotates on its axis, you see two maximums — when looking at the two broadsides of the potato, — and two minimums — when looking down the length at either end of the potato. Now imagine what you would see when looking at the potato from the top, when the spin axis is on the line of sight. In this case, you see very little, if any, variations. Now, imagine the curve if the axis was pointing somewhere between these two extremes or if the potato was partly peeled. Go further and try to imagine the curve if the asteroid is shaped more like a dog-bone, or a three- or foursided pyramid, or a highly irregular chunk created by the collision between two asteroids.

By using the refined inversion process, the researcher can use the changing amplitude of the curve for each apparition and determine the pole orientation. With enough curves, the shape of the asteroid can be found. Often five to seven curves are just enough. Of course, there is a point of diminishing returns but that is rarely reached since many lightcurve observers make the mistake of assuming that once the period is determined yet another curve has no significant value. This paper set back asteroid lightcurve studies for nearly 75 years, until some more careful analysis and research showed that asteroids, through the collisional erosion process, paint themselves to an almost uniform gray.

There can be albedo differences from one asteroid to the next, but to a very good approximation, each asteroid can be considered uniform in color and brightness. Now, several dozen asteroids are known to be binaries. This is the rate below which centrifugal force would cause a loose conglomerate of rocks to fly apart against its own self-gravity.

This lends further support to the rubble pile structure of even small asteroids. On the other hand, a number of asteroids have been found with periods considerably less than 2. These must be monolithic rocks and not rubble piles or they would fly apart.

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What are they and why are they important? The H value is the absolute magnitude of the asteroid. There is a direct, though complex, correlation between H and the size of the asteroid, one that accounts for the albedo, which is the ratio of sunlight reflected versus received. Having an accurate H value gives the approximate size. This helps establish the correlation between size and rotation rate. It also helps establish the size against taxonomic class, orbit parameters, and other factors.

go to link If simple geometry were all that was needed to predict the brightness of an asteroid, the H value along with Sun and Earth distances would be sufficient to make that calculation. However, there is a dependency on the phase angle of the 10 Targets of Opportunity — Asteroids asteroid, which is described by the value G. The term slope parameter comes from the fact the magnitude-phase relationship is nearly linear and so a plot is a line with a constant slope.

The opposition effect causes asteroids and the moon, too to be brighter at small phase angles. In general, the cause of the effect deals with the way light is reflected and scattered when the source of illumination is nearly perpendicular to the illuminated surface. So, how does getting a lightcurve help determine these values? G is the slope of the line from that solution. This gives the value of H.

The H and G values are measured in the standard Johnson V band. This means that if you plan to determine these values in addition to the period, you must have at least some measurements that are in or can be reduced to this band. A considerable amount of information about the asteroid can be determined by measuring what happens to the frequency of the returned signal changed by the Doppler effect and the time it takes the signal to go to the asteroid and return.

These are not true images in the usual sense of looking through an optical telescope. Instead they represent fre- Targets of Opportunity — Asteroids 11 quency shift and distance. Ground-based lightcurve observations can help establish limiting parameters before radar observations begin, allowing the astronomers to determine if the radar observations have a reasonable chance of providing useful data. For example, if the asteroid is rotating too slowly, the frequency shift caused by rotation may be difficult to detect since it is so small.

Lightcurve observations obtained at the same time as the radar observations are also used to help constrain the results found by the radar observations. All of these skew the results of studies using rotation rates and may lead to inaccurate conclusions about the formation of the asteroid system. As noted above, there appears to be a barrier regarding rotation rate and size. There may be other barriers or plateaus not yet recognized because there is insufficient data.

Working faint targets means noisier data.

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As shown in Fig. However, by getting a number of runs, the noise averaged out and the period analysis code was able to determine the period with a high degree of precision. Figure 2.