better alt text ch5 (#240)

Author: pancakereport

chapters/05/3/More_on_Arrays.ipynb

@@ -138,7 +138,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "![array subtraction](../../../images/array_subtraction.png)"
+    "![Illustration of array subtraction. The highs array is shown on the left followed by a subtraction sign and then the lows array. The arrays are aligned so the numbers in the first position of the array are next to each other, same for the second, third, and fourth positions. Following that is an equal sign and an array representation with the first entry of lows subtracted from the first entry of highs, and the same for the second, third, and fourth entries. Following that is another equal sign with an array showing the result of the subtraction in each entry of the array.](../../../images/array_subtraction.png)"
    ]
   },
   {

chapters/05/Sequences.ipynb

@@ -88,11 +88,11 @@
     "\n",
     "**Mean of Daily High Temperature**\n",
     "\n",
-    "![Mean of Daily High Temperature](../../images/global-land-TMAX-Trend.png)\n",
+    "![Plot titled \"Global Land\" and annotated \"Berkeley Earth Surface Temperature.\" On the x-axis years are labeled from 1820 to 2000. On the y-axis the High Temperature (degrees Celsius). A dark blue line shows the 12-month moving average and a red line shows the 10-year moving average with a 95% uncertainty range. The blue line bounces above and below the red line but tends to follow it. The lines were lowest at the beginning of the data, around 13.5 to 14.5 degrees before 1940. From about 1970, the lines tend upward, increasing from about 14.5 degrees to almost 15.5 degrees.](../../images/global-land-TMAX-Trend.png)\n",
     "\n",
     "**Mean of Daily Low Temperature**\n",
     "\n",
-    "![Mean of Daily Low Temperature](../../images/global-land-TMIN-Trend.png)"
+    "![Plot titled \"Global Land\" and annotated \"Berkeley Earth Surface Temperature.\" On the x-axis years are labeled from 1820 to 2000. On the y-axis the High Temperature (degrees Celsius). A dark blue line shows the 12-month moving average and a red line shows the 10-year moving average with a 95% uncertainty range. The lines show variability, but stay below 3 degrees until about 1940. More recent data post-1970 has an upward trend ending around 4 degrees.](../../images/global-land-TMIN-Trend.png)"
    ]
   }
  ],