偷针眼怎么引起的:预报并显示人造卫星过境

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Predicting and displaying satellite passes
The most useful satellite operation offered by SkyMap is its ability to predict and display the "pass" (ie the appearance) of a satellite as seen from a specific location. Satellite passes can be displayed in a tabular format, or the track of a specific satellite pass can be plotted as a line on the star chart.
预报并显示人造卫星过境
skymap所提供的有关卫星的最有用的功能就是预报并显示在特定区域可以看到的卫星过境。卫星过境可以通过表格显示，或者可以用一条曲线描绘在星图上。
In order to be seen, a satellite pass has to satisfy several conditions:
First and most importantly, the satellite must rise above the observer's horizon. For satellites in low orbit, this generally means that the observer's latitude must be within the range of latitudes over which the satellite passes. A satellite will pass over (at some time or another) every point on the Earth's surface whose latitude is less than or equal to the satellite's orbital inclination. For example, a satellite with an orbital inclination of 30o can be seen from any latitude between roughly 30oN and 30oS, so it will never be visible for an observer at 50oN. The higher the satellite's orbit, the greater is the distance outside its ground track from which it can be seen. The Ground Track menu command can be used to view the ground track of any satellite. The satellite must be sunlit. The observer must be in darkness, or at least twilight, so that the satellite is visible against a dark sky.
满足以下几个条件，过境卫星才能被观测到：
首先，也是最主要的，卫星必须在观测者的地平线之上。对于低轨运行的卫星，这通常意味着如果要观察到它，观测者的纬度必须要高于卫星轨道的纬度才可以。卫星将会经过地球表面纬度小于或等于卫星轨道倾角的所有的点。比如，一个轨道倾角是30o的人造卫星就可以在30oN 和 30oS之间的观测者观测到。所以，对于50oN的观测者是永远不能观测到这颗卫星的。人造卫星的轨道越高，它与地面轨迹之间的距离就越远。地面轨迹选单就是用来查看人造卫星地面轨迹的。 人造卫星必须被日光照射 观测者必须在夜晚观测，或者最起码是在黄昏，因为只有这样，人造卫星才能与暗背景形成对比而被观察到。
A pass of a satellite occurs whenever it rises above the observer's horizon; a "visible pass" occurs when all three of the above conditions are satisfied, so the sunlit satellite is seen against a dark sky - this will generally occur either shortly after sunset, or shortly before sunrise. In most cases, the satellite will rise in the west, cross the observer's meridian, and set in the east, although satellites in a polar orbit can rise or set in any part of the sky! Very often the satellite won't be visible for the whole of its passage across the sky, but will either emerge from or enter into the Earth's shadow while above the horizon.
不论卫星何时从观测者地平线之上穿过，都会形成卫星路径；但是卫星经过的“可见路径”只有在满足上面所有三个条件的时候才可以形成，有此看来，只有被日光照射的人造卫星必须与暗背景对比才能被观测到-这经常要在太阳刚刚落山或者太阳将要升起之前。大多数情况下，人造卫星自观测者的西方升起，经过中天，然后在东方落下，虽然越极轨道人造卫星可以在天空的任意部分升起和落下！地平线上的人造卫星在进入或离开地球阴影的时候被观测到，但是在大多数情况下，人造卫星在它穿越天空的时候是观测不到的。
Entering information To predict satellite passes for the observation location set up on the current star chart, select the Tools/Satellites/Pass Prediction... menu item to display the first page of the Pass Prediction Dialog :
输入信息
为了预测以星图设定的地点为观测点的卫星过境，选择工具/人造卫星/经过预报... 显示经过预报对话框：

This page of the dialog allows you to enter all the information required by SkyMap to predict satellite passes. There are two basic types of prediction available, selected in the Satellite Selection section of the dialog:
You can predict all the passes of a specific satellite for a time period of several days or weeks. If you select this option, highlight the name of the satellite in the list at the left side of the dialog. You can predict passes of all the satellites in the current data file for a single day. In this case, the selection in the list, if present, is ignored.
在此页输入skymap进行预测所需的所有信息。有两种基本的预报形式，选择人造卫星选择选项：
你可以预测一颗指定的卫星在几天或几周内的所有过境信息。如果你选择这个选项，在目录中选择卫星名称，使它高亮显示。 你可以约测所有卫星在今天或特定一天的过境信息。在这个情况下，如果你在目录中进行了选择，是会被忽略的。
The Time section at the top of the dialog allows you to set time information for the pass. The standard date selector allows you to select the starting date for the pass predictions; the Display positions every... field allows you to set the frequency with which positions of the satellite are calculated during a pass; the smaller the time interval, the smoother will be the line on the star chart, at the expense of increased calculation time. For a satellite in low Earth orbit, the default time interval of 15 seconds will normally be acceptable, but for a geostationary satellite this should be increased to 60 seconds or more.
设定时间选项。
The Options section at the bottom of the dialog allows you to select several options for pass prediction:
The Show only visible passes check box allows you to select whether all passes of the satellite are displayed, or only visible passes. SkyMap defines a visible pass as one in which the satellite is sunlit, and the Sun at the observer's location is at least 6o below the horizon. The Show only passes with a minimum altitude check box allows you to display only those passes during which the satellite reaches at least the specified minimum altitude above the observer's horizon.
Displaying a tabular list of passes To display information about satellite passes in a tabular form, click the Table tab at the top of the dialog after entering all the required information on the Select page; the passes will be calculated (which may take a while on a slow computer) and the results will be displayed in the form of a table:
For each pass, the table first displays the name of the satellite, and then shows one or more lines of information about that pass of the satellite. The information can be shown in two formats, selected by the Summary and Full buttons immediately below the table:
If the Summary display option is selected, information will be displayed only for the beginning of the pass, the time at which the satellite reaches its maximum altitude above the observer's horizon, and the end of the pass. This is generally the more useful option since it presents the most useful information in a compact manner. Note that the pass may either begin or end with the satellite above the horizon, and the time of maximum altitude may be coincident with the beginning or end of the pass, due to the satellite emerging from or entering into the Earth's shadow at that point. If the Full display option is selected, information will be displayed for every calculated point during the pass; the time interval between these points will be the interval specified in the Time section of the Select page of the dialog. You will probably not often wish to display full details - a much better idea of the path taken by the satellite can be obtained by plotting its track on the star chart, as described below.
For each displayed point on the track, the following information is shown: Time The date and time at which the satellite is at this point on the pass. This is always displayed in the time zone set up for the current star chart.
Alt/Az The altitude and azimuth of the satellite relative to the observer's horizon, measured in degrees.
Range The distance of the satellite from the observer, in whatever units have been set up on the Satellite Configuration Dialog.
Rate The rate at which the satellite is approaching (if negative) or receding from (if positive) the observer, again in the units specified on the Satellite Configuration Dialog .
Vis The satellite's visibility. If the satellite is sunlit, this column will be blank. Values of "PEN" or "UMB" indicate that the satellite is in the Earth's penumbral or umbral shadows respectively. If only visible passes have been requested, this column will always be blank.
The Save and Copy buttons allow you to save the pass list to a text file or to copy it to the Windows clipboard respectively. The Time + and Time - buttons repeat the pass calculation, moving the date either forward or backward. The date will move one day forward or backward if passes of all satellites are being predicted, or will move by whatever number of days is set up on the Select page of the dialog if passes for a single satellite are being predicted. Displaying satellite tracks on the map In addition to being able to display the times of satellite passes in a tabular format, SkyMap also allows you to plot the "track" of one or more satellite passes on the star chart, so you can see whereabouts in the sky the satellite will appear. To do this, exit the pass prediction dialog by clicking the OK button (if you wish to exit without plotting pass tracks on the star chart, exit by clicking the Cancel button); the Satellite Pass Plot Selection Dialog will be displayed:

For each satellite pass, the dialog displays the name of the satellite and the date and time of the start of the pass; the list can be sorted in order of either name or time - as usual, click the column header to sort the list in order of that column, and click the column header a second time to reverse the sort order. To select a pass for display on the star chart, check the box alongside that line in the list. Clicking the Select All button will select all passes in the list for display; clicking the Select None button will remove the check mark from every line in the list. The Label position every... field below the list allows you to choose the time interval at which points on the satellite track will be labelled with the time. Only points for which a position can been calculated can be labelled, so this time interval should be an exact multiple of the calculation interval specified on the pass prediction dialog. If you don't want any time labels to appear on the track, enter a labeling interval of zero. After selecting the passes to be displayed, exit the dialog by clicking the OK button; the satellite tracks will be displayed as lines on the star chart. The name of the satellite and the date of the start of the pass will be shown alongside the start of the track, while other points on the track will be labelled only with the time. It's important to note that when satellite tracks are displayed on a star chart, what is shown is the path of the satellite relative to the stars. Since the chart will almost certainly not be showing the sky for the time of the predicted pass, the position of the satellite relative to the horizon (which is normally of much greater interest) will not be correct. Although you could manually change the map time to match that of the desired satellite track, we've provided a "short-cut" method of doing this. Simply position the mouse pointer over any point on the satellite track which is labelled with a time, click the right mouse button, and select Track Time from the resulting pop-up menu. The map time will be set to that of the point clicked on, and the satellite track will now be displayed correctly relative to the observer's horizon. For example, when the above passes are initially shown on the star chart, we might see (on a "zenith" map view) the two tracks looking something like this:

This shows us the correct path of the satellite against the constellations, but doesn't show us the correct path relative to the horizon, because the map is not being displayed for the time of the satellite track. To display the "upper" of these two tracks correctly relative to the horizon, we position the mouse pointer over a time roughly in the middle of the track, right click, and select Satellite Track Time:

This results in the map being redrawn for the selected time, and we now see the track in the correct position relative to the horizon:

We can now clearly see that the satellite rises almost due west at 01:52, passes high overhead (travelling almost exactly midway between Altair and Vega), and sets slightly to the south of due east at 02:02. We could now repeat this process to display the other satellite track on the map in its correct position relative to the horizon. Removing tracks from the map To remove satellite tracks from the map, select the View/Clean Up Map menu item.
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