Image at top: Last quarter moon in spring, by Chirag Upreti in the Bronx, New York.
A last quarter moon rises around midnight (1 a.m. if you’re on Daylight Time). The last quarter moon you’ll see late at night on April 7 (or early in the morning on April 8) is aligned with 2018’s closest apogee, that is, the closest of the moon’s farthest points in its monthly orbit. And that’s no surprise, because the year’s closest apogee often aligns with the quarter moon.
There will be a total of lunar apogees in 2018. That is, 13 times this year, the moon will swing out to the farthest point in its monthly orbit. See a list of 2018’s 13 apogees here.
But – as often happens – it’s this month’s lunar apogee, the one most closely aligning with the quarter moon, that gives us the year’s closest far moon. This is easily the year’s closest coincidence of quarter moon and lunar apogee, with the two events taking place less than two hours apart:
Last quarter moon: April 8, 2018, at 7:18 UTC
Lunar apogee: April 8, 2018, at 5:32 UTC (404,114 km)
At U.S. times zones, the moon reaches its last quarter phase on April 8, at 3:18 a.m. EDT, 2:18 a.m. CDT, 1:18 a.m. MDT and 12:18 a.m. PDT.
But that’s not all. The lunar perigee – the moon’s closest point to Earth in its monthly orbit – aligning most closely with the quarter moon often presents the year’s farthest perigee (near moon).
Seven lunar months (7 returns to last quarter moon) after this last quarter moon on April 8, 2018, the last quarter moon will pair up with lunar perigee (instead of lunar apogee) on October 31, 2018. Of 2018’s 14 perigees, the last quarter moon on October 31, 2018, will coincide with the most distant perigee (close moon) of 2018.
Last quarter moon: October 31, 2018, at 16:40 UTC
Lunar perigee: October 31, at 20:05 UTC (370,204 km)
Want to know when the closest apogee and farthest perigee will happen in 2019? There’s a lunar cycle whereby 14 lunar months almost exactly equal 15 returns to perigee (or apogee). A lunar month refers to the time period between successive returns to the same phase, a mean period of 29.53059 days. An anomalistic month refers to successive returns to perigee (or successive returns to apogee), a period of 27.55455 days. Hence:
14 lunar months (returns to last quarter moon) x 29.53059 days = 413.428 days
15 anomalistic months (returns to lunar apogee) x 27.55455 days = 413.318 days
Therefore, the last quarter moon and lunar apogee will realign in a period of about 413 days (one year, one year and 18 days). We can expect the last quarter moon to showcase 2019’s closest apogee (far moon) on May 26, 2019; and then for the last quarter moon to present 2019’s farthest perigee (close moon) on December 18, 2019.
Bottom line: The last quarter moon you’ll see late at night on April 7 (or early in the morning on April 8) is aligned with 2018’s closest apogee, that is, the closest of the moon’s farthest points in its monthly orbit. And that’s no surprise, because the year’s closest apogee often aligns with the quarter moon.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.