3下表为地球在公转轨道不同位置时公转速度的变化资料，据此比较北极和南极极夜持续天数。<table style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; BORDER-COLLAPSE: collapse; BORDER-TOP: medium none; BORDER-RIGHT: medium none; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" border="1" cellspacing="0" cellpadding="0" _dj="MsoNormalTable"><tbody><tr style="HEIGHT: 14.5pt; mso-yfti-irow: 0; mso-yfti-firstrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 95.8pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt" valign="top" width="128">时间</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 85pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt" valign="top" width="113">日地距离</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 63.75pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt" valign="top" width="85">角速度</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 69.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt" valign="top" width="92">线速度</td></tr><tr style="HEIGHT: 14.5pt; mso-yfti-irow: 1"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 95.8pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="128">1月初（近日点）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 85pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="113">1.471亿km</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 63.75pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="85">61′/d</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 69.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="92">30.3km/s</td></tr><tr style="HEIGHT: 14.5pt; mso-yfti-irow: 2; mso-yfti-lastrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 95.8pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="128">7月初（远日点）</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 85pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="113">1.521亿km</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 63.75pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="85">57′/d</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 69.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 14.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" valign="top" width="92">29.3km/s</td></tr></tbody></table>