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</textobject><caption><para><ulink url="cel://PhaseLock/Sol:Jupiter:Io//2003-01-30T08:22:03.99?x=2HPYJQ8gkqeEDA&y=nObZfKeMKQUB&z=ZdL5mSrk6njC/////////w&ow=0.948617&ox=-0.019555&oy=-0.314877&oz=-0.024411&select=Sol:Jupiter:Io&fov=19.402893&ts=10.000000&rf=57239&lm=0">Io eclipsing Jupiter, an example of Eclipse Shadows.</ulink></para></caption></mediaobject></screenshot></entry><entry><screenshot><screeninfo>A total solar eclipse over Africa, as seen from space.</screeninfo><mediaobject><imageobject><imagedata fileref="fig12.jpg" format="PNG" /></imageobject><textobject><phrase>A total solar eclipse over Africa, as seen from space.</phrase></textobject><caption><para><ulink url="cel://PhaseLock/Sol:Earth//2006-03-29T10:00:10.14?x=CJhT/kKTMRGuDA&y=Trq1EVGVMg&z=92vpvZKWWFQC&ow=0.633311&ox=0.076168&oy=-0.767258&oz=-0.066564&select=Sol:Earth&fov=19.402893&ts=1.000000&rf=57239&lm=0">A total solar eclipse over Africa, as seen from space.</ulink></para></caption></mediaobject></screenshot></entry></row></tbody></tgroup></informaltable></sect1><sect1 id="opt_galaxies"><title>Galaxies (&galaxies;)</title><para>&celestia; comes with a galaxy data file that tells the program the position of numerous galaxies in the night sky and what type they are. When this option is selected, &celestia; will create a small, dim sketch of each galaxy and position it in the proper place in space. It will also draw the huge band of starry haze we know as the Milky Way. Selecting the option, therefore, will improve your &celestia; experience and you will be able to see dim galaxies in the distance. You can even travel to them in your spaceship. However, the galaxy sketches are simple and appear as dim "blobs". Later versions of &celestia; will improve on the graphics of galaxies.</para><para><emphasis>Recommended</emphasis> - but does require computer resources. Try turning off if &celestia; is running too slowly.</para><informaltable pgwide="1"><tgroup cols="2"><tbody><row><entry><screenshot><screeninfo>Neptune and Milky Way with Galaxies enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig13.jpg" format="PNG" /></imageobject><textobject><phrase>Neptune and Milky Way with Galaxies enabled.</phrase></textobject><caption><para><ulink url="cel://PhaseLock/Sol:Neptune//2006-03-29T10:01:33.81?x=2Gskq/E6DO4bDg&y=ir4/pNxkBYn+/////////w&z=VXCvtfOiV8ZAAQ&ow=0.017244&ox=-0.142499&oy=-0.989644&oz=-0.000777&select=Sol:Neptune&fov=20.674709&ts=1.000000&rf=57239&lm=0">Neptune and Milky Way with Galaxies enabled.</ulink></para></caption></mediaobject></screenshot></entry><entry><screenshot><screeninfo>Same scene without Galaxies enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig14.jpg" format="PNG" /></imageobject><textobject><phrase>Same scene without Galaxies enabled.</phrase></textobject><caption><para><ulink url="cel://PhaseLock/Sol:Neptune//2006-03-29T10:01:48.90?x=cLQ0q1GcDO4bDg&y=6jGoRGVgBYn+/////////w&z=VcNKIyo3V8ZAAQ&ow=0.017244&ox=-0.142499&oy=-0.989644&oz=-0.000777&select=Sol:Neptune&fov=20.674709&ts=1.000000&rf=57235&lm=0">Same scene without Galaxies enabled.</ulink></para></caption></mediaobject></screenshot></entry></row></tbody></tgroup></informaltable></sect1><sect1 id="opt_night_side_lights"><title>Night Side Lights (&nightsidelights;)</title><para>&celestia; has the ability to light up the night sky. From space, the thousands of cities across our continents are ablaze with light so bright that they can be seen vividly from hundreds of km up. Turning on this option commands &celestia; to add those lights to the nighttime vista you see from space above Earth. Night textures are also used in some add-ons to show fictional cities or volcanic lava flows at night.</para><para><emphasis>Highly Recommended</emphasis> - but does require computer resources. Note: On older video cards, night-side lights may slow down the program. Try turning off if &celestia; is running too slowly.</para><informaltable pgwide="1"><tgroup cols="2"><tbody><row><entry><screenshot><screeninfo>Earth, Sun and terminator with night-lights enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig15.jpg" format="PNG" /></imageobject><textobject><phrase>Earth, Sun and terminator with night-lights enabled.</phrase></textobject><caption><para><ulink url="cel://Follow/Sol:Earth/2006-03-29T04:38:33.20?x=2E27BL0aqA2uDA&y=M4QqEncs3////////////w&z=g6SKdIqs2kQC&ow=0.633149&ox=0.213732&oy=0.692488&oz=-0.271848&select=Sol:Earth&fov=20.674709&ts=1.000000&rf=57239&lm=0">Earth, Sun and terminator with night-lights enabled.</ulink></para></caption></mediaobject></screenshot></entry><entry><screenshot><screeninfo>Same scene without night-lights enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig16.jpg" format="PNG" /></imageobject><textobject><phrase>Same scene without night-lights enabled.</phrase></textobject><caption><para><ulink url="cel://Follow/Sol:Earth/2006-03-29T04:38:51.19?x=2E1CQPuTqA2uDA&y=a2vZXHEs3////////////w&z=g6RQFYpc3kQC&ow=0.633149&ox=0.213732&oy=0.692488&oz=-0.271848&select=Sol:Earth&fov=20.674709&ts=1.000000&rf=57111&lm=0">Same scene without night-lights enabled.</ulink></para></caption></mediaobject></screenshot></entry></row></tbody></tgroup></informaltable></sect1><sect1 id="opt_orbits"><title>Orbits (&orbits;)</title><para>&celestia; will draw the actual path of a planetary orbit through the solar system. The Option also draws orbits of all moons, comets, asteroids and spacecraft that you choose. Each orbit type is drawn in a different color, with the active orbits in red. For example, if you are centered on Venus and have ?planet? orbits selected, Venus?s orbit will be highlighted in red. All other planet orbits will be highlighted in blue. Orbits are excellent for seeing the celestial mechanics of the solar system. Turn them on, zoom out from the Sun and view the orbits from above. Speed up time (see later discussion) and you will see the alignment of planets speeding around the Sun, or view the orbits of satellites as they circle around a planet. The Orbit/Label section of the <guimenu>View Options</guimenu> Menu allows you to turn specific orbit types on or off with a check mark in the box.</para><para><emphasis>Recommended</emphasis> - when desired. Does not use much computer resources.</para><screenshot><screeninfo>Solar System with orbits enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig17.jpg" format="PNG" /></imageobject><textobject><phrase>Solar System with orbits enabled.</phrase></textobject><caption><para><ulink url="cel://Follow/Sol/2006-03-29T04:39:48.33?x=AAAgHOqyiGVUCQ&y=CkzQLZRSPWnc&z=VcpQPfVHxHG59////////w&ow=0.219300&ox=-0.005459&oy=0.973495&oz=0.064688&select=Sol&fov=20.674709&ts=1.000000&rf=57271&lm=0">Solar System with orbits enabled.</ulink> The inclined orbit is that of Pluto, a large Kuiper Belt Object that may have swung into its current orbit through a past collision with another object.</para></caption></mediaobject></screenshot></sect1><sect1 id="opt_planets"><title>Planets</title><para>Normally selected. <emphasis>Highly Recommended.</emphasis></para></sect1><sect1 id="opt_ring_shadows"><title>Ring Shadows</title><para>&celestia; can compute and draw the actual position of the shadows a planet's ring will cast on a planet below and conversely, the shadow a planet will cast on its rings.</para><para><emphasis>Highly Recommended</emphasis> - but does require significant computer resources.</para><note><para>On some older video cards, ring shadows have also been known to slow down the program dramatically or lock it up entirely.</para></note><informaltable pgwide="1"><tgroup cols="2"><tbody><row><entry><screenshot><screeninfo>Ring Shadows enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig18.jpg" format="PNG" /></imageobject><textobject><phrase>Ring Shadows enabled.</phrase></textobject><caption><para><ulink url="cel://Follow/Sol:Saturn/2006-03-29T04:40:33.59?x=gJW90XX90hlhDA&y=CpSPoBqCgcYB&z=JXaSk5dugImR/////////w&ow=-0.647476&ox=-0.274139&oy=0.707176&oz=-0.074328&select=Sol:Saturn&fov=20.674709&ts=1.000000&rf=57239&lm=0">Ring Shadows enabled.</ulink></para></caption></mediaobject></screenshot></entry><entry><screenshot><screeninfo>Same scene without night-lights enabled.</screeninfo><mediaobject><imageobject><imagedata fileref="fig19.jpg" format="PNG" /></imageobject><textobject><phrase>Ring Shadows disabled.</phrase></textobject><caption><para><ulink url="cel://Follow/Sol:Saturn/2006-03-29T04:40:49.83?x=gJUtN50Z0hlhDA&y=CnRQz0uOgcYB&z=JXaSIiIigYmR/////////w&ow=-0.647476&ox=-0.274139&oy=0.707176&oz=-0.074328&select=Sol:Saturn&fov=20.674709&ts=1.000000&rf=53143&lm=0">Ring Shadows disabled.</ulink></para></caption></mediaobject></screenshot></entry></row></tbody></tgroup></informaltable></sect1><sect1 id="opt_stars_as_point"><title>Stars As Discs or Points (&starsaspoints;)</title><para>&celestia; can display stars either as points, scaled discs or fuzzy points. Which looks better is a matter of personal taste and the resolution of your monitor. In general, a scaled disc forms a prominent circular disc that varies in both diameter and brightness based upon the actual size, magnitude and distance of the star from you. For example, a bright Red Giant s⌨️ 快捷键说明
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