Photo from per.olesen’s photostream
For people living around 40 degrees north latitude, the latest sunsets of the year happen in late June. And in the Southern Hemisphere, at 40 degrees south latitude, it’s the year’s latest sunrises that happen around this time of year. That’s in spite of the fact that the longest (or shortest) day of the year falls on the June 20 solstice.
Although the latest sunset always comes on or near June 27 at mid-northern latitudes every year, the sky scene in the southwestern sky after sunset is special to June 27, 2012. As darkness falls at northerly latitudes, look for the waxing gibbous moon to shine in the vicinity of the planet Saturn and Spica, the constellation Virgo’s brightest star. For more on Saturn and Spica, see tomorrow’s program.
The year’s latest sunset always comes after the summer solstice, even though the exact date depends on your latitude. Farther north – at Seattle – the latest sunset happens a few days before June 27. Farther south at Mexico City, the latest sunset won’t happen until early July.
The latest sunsets come after the summer solstice because the day is more than 24 hours long at this time of the year. In June and July, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later in late June by the clock than it does on the June 20 solstice. Therefore, the sunrise and sunset times also come later by the clock, as the table below helps to explain.
For Denver, Colorado
| Date | Sunrise | Midday (Solar Noon) | Sunset | Daylight Hours |
| June 20 | 5:32 a.m. | 1:02 p.m. | 8:31 p.m. | 14h 59m 19s |
| June 27 | 5:34 a.m. | 1:03 a.m. | 8:32 p.m. | 14h 57m 55s |
Source: timeanddate.com
If the Earth’s axis stood upright as our world circled the sun, and if, in addition, the Earth stayed the same distance from the sun all year long, then clock time and sun time would always agree. However, the Earth’s axis is titled 23.5 degrees out of vertical, and our distance from the sun varies by about 3 million miles throughout the year. At and around the equinoxes, solar days are shorter than 24 hours, yet at the solstices, solar days are longer than 24 hours.
In a nutshell, it’s the discrepancy between the sun and the clock that brings a later sunset in late June than on the exact day of the summer solstice.
