Wednesday, May 23, 2018

May 2018 Lunar Perigee Happened Thursday, May 17, During Eta Aquarids


Summary: May 2018 lunar perigee happened Thursday, May 17, at the month’s closest Earth-moon center-to-center distance of 363,777 kilometers.


waxing crescent moon Thursday, May 17, at 21:00 UTC (5 p.m. EDT), six minutes before May’s lunar perigee: Ernie Wright (USRA lead visualizer), John Keller (NASA GSFC scientist), Noah Petro (NASA GSFC scientist) and David Ladd (USRA producer) via NASA/Goddard Space Flight Center Scientific Visualization Studio

May 2018 lunar perigee happened Thursday, May 17, during the Eta Aquarid meteor shower, at the month’s closest Earth-moon center-to-center distance of 363,777 kilometers (226,040.548 miles), at 21:06 Coordinated Universal Time/Greenwich Mean Time (5:06 p.m. Eastern Daylight Time).
May 2018’s lunar perigee of 363,777 kilometers is 4,936 kilometers closer to Earth than April 2018’s lunar perigee of 368,713. April’s lunar perigee happened Friday, April 20, at 14:44 UTC/GMT (10:44 a.m. EDT).
May 2018’s lunar perigee of 363,777 kilometers is 4,270 kilometers farther from Earth than June 2018’s lunar perigee of 359,507 kilometers. June’s lunar perigee occurs Thursday, June 14, at 23:55 UTC/GMT (7:55 p.m. EDT).
Each month the center-to-center distance between Earth and Earth’s moon logs two maximums. Perigee (Ancient Greek: περί, perí, “near” + γῆ, gê, “Earth”) designates the closest center-to-center distance between moon and Earth. The opposite maximum is apogee (Ancient Greek: ἀπόγειον, apógeion, “away from Earth” + ἀπό, apó, “away” + γῆ, gê, “Earth”), which references the farthest center-to-center distance between moon and Earth.
Astronomers also note the minimum and maximum values for each year’s perigee and apogee. Maximum perigee represents the farthest center-to-center distance in the closeness range. Minimum perigee indicates the closest center-to-center distance in the closeness range. Closest perigee for the year is known as proxigee.
Maximum perigee, or farthest perigee, for 2018 happens Wednesday, Oct. 31, at 20:05 UTC/GMT (4:05 p.m. EDT) and spans an Earth-moon center-to-center distance of 370,201 kilometers. The year’s maximum perigee of 370,201 kilometers is 6,424 kilometers farther from Earth than May’s lunar perigee of 363,777 kilometers.
The moon obtained 2018’s minimum perigee, or closest perigee, Monday, Jan. 1, at 21:54 UTC/GMT (4:54 p.m. Eastern Standard Time). The minimum perigee for 2018 is 356,566 kilometers. The year’s minimum perigee of 356,566 kilometers is 7,211 kilometers closer to Earth than May’s lunar perigee of 363,777 kilometers.
The moon phase at May 2018’s lunar perigee was waxing crescent, with about 6 percent visibility of the lunar surface for Earth’s observers. Waxing crescent numbers second in the moon’s eight-phase cycle. The waning crescent phase follows the darkened new moon and transitions to the first quarter phase of half illumination.
April 2018’s lunar perigee took place also with a waxing crescent moon. A new moon hosts June 2018’s lunar perigee. The year’s minimum, or closest, perigee, which happened in January, occurred during the fifth phase’s full moon. The year’s maximum, or farthest, perigee, expected in October, coincides with the seventh phase’s last quarter moon.
May 2018’s perigeic waxing crescent moon balanced the apogeic waning gibbous moon Sunday, May 6, that offered a troublesome glare for Earth observers watching for Eta Aquarid shooting stars. Apogee's largely darkened moon set in the evening, long before the best hours for meteor shower viewing.
The Eta Aquarids’ annual display of showering meteors takes place from mid-late April to mid-late May, from around April 19 to around May 28. Peak viewing, which usually happens around May 5 or 6, tends to promise especially good hourly rates. Interference with easy viewability comes from cloud cover or from a bright, day-setting moon, such as May 6’s waning gibbous.
The Eta Aquarid meteor shower is named for Eta Aquarii (η Aqr, η Aquarii) in Aquarius the Cup Bearer, or Water Carrier, constellation. The path of Eta Aquarid meteors appears to trace back in the night sky to a point near Eta Aquarii. The point of origin, known as the meteor shower’s radiant, is only a visual perception.
In reality, the Eta Aquarid meteor shower originates in debris from Halley’s Comet. The short-period comet, with an orbital period of 74 to 79 years, is also associated with another meteor shower. The Orionids shower Earth between September and November, with peak activity in late October.
The takeaway for May 2018 lunar perigee is that the month’s closest Earth-moon center-to-center distance happened Thursday, May 17, while Eta Aquarid meteors still showered Earth’s night skies.

EarthSky @EarthSky. "Get up before dawn and look for meteors. Eta Aquarids are at their peak! The radiant point of Eta Aquarid meteor shower is in the constellation Aquarius, in the southeast before dawn, as seen from mid-northern latitudes." Facebook. May 4, 2014

Acknowledgment
My special thanks to:
Talented artists and photographers/concerned organizations who make their fine images available on the Internet;
Virginia Polytechnic Institute and State University for superior on-campus and on-line resources.
Image credits:
waxing crescent moon Thursday, May 17, at 21:00 UTC (5 p.m. EDT), six minutes before May’s lunar perigee: Ernie Wright (USRA lead visualizer), John Keller (NASA GSFC scientist), Noah Petro (NASA GSFC scientist) and David Ladd (USRA producer) via NASA/Goddard Space Flight Center Scientific Visualization Studio @ https://svs.gsfc.nasa.gov/4604

For further information:
EarthSky @EarthSky via Facebook post May 4, 2014, @ https://www.facebook.com/EarthSky/photos/a.61619521852.81951.36709031852/10151984615951853/
EarthSky @EarthSky. "Get up before dawn and look for meteors. Eta Aquarids are at their peak!  The radiant point of Eta Aquarid meteor shower is in the constellation Aquarius, in the southeast before dawn, as seen from mid-northern latitudes." Facebook. May 4, 2014.
Available @ https://www.facebook.com/EarthSky/photos/a.61619521852.81951.36709031852/10151984615951853/
Espenak, Fred. “Moon at Perigee and Apogee: 2001 to 2100 Greenwich Mean Time.” Astro Pixels > Ephemeris > Moon.
Available @ http://astropixels.com/ephemeris/moon/moonperap2001.html
Espenak, Fred. “2018 Calendar of Astronomical Events Greenwich Mean Time.” Astro Pixels > Ephemeris.
Available @ http://astropixels.com/ephemeris/astrocal/astrocal2018gmt.html
Marriner, Derdriu. “February 2018 Lunar Perigee Is Tuesday, Feb. 27, at 363,938 Kilometers.” Earth and Space News. Wednesday, Feb. 21, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/02/february-2018-lunar-perigee-is-tuesday.html
Marriner, Derdriu. “March 2018 Lunar Apogee Is Sunday, March 11, at 404,682 Kilometers.” Wednesday, March 7, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/03/march-2018-lunar-apogee-is-sunday-march.html
Marriner, Derdriu. “May 2018 Lunar Apogee Happens Sunday, May 6, During Eta Aquarids.” Earth and Space News. Wednesday, May 2, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/05/may-2018-lunar-apogee-happens-sunday.html
McClure, Bruce. “Close and Far Moons in 2018.” EarthSky > Astronomy Essentials. Jan. 15, 2018.
Available @ http://earthsky.org/astronomy-essentials/close-and-far-moons
“Moon Phases May 2018.” Calendar-12.com > Moon Calendar > 2018.
Available @ https://www.calendar-12.com/moon_calendar/2018/may
Wright, Ernie. “Moon Phase and Libration, 2018.” NASA Scientific Visualization Studio/Planets and Moons.
Available @ https://svs.gsfc.nasa.gov/4604

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