Apparent size of a full supermoon, or close moon, contrasted with a full micro-moon, or far moon. Image by Peter Lowenstein.
The 11th of 2017’s 12 full moons falls on November 3-4; click here to learn the exact time of full moon. This full moon ranks as the second-closest one of 2017, but it’s less than clear whether it should be dubbed a supermoon, mainly because people disagree on what constitutes a supermoon. Follow the links below to learn more.
Who are the commentators, and what do they say?
Original definition of supermoon
Nolle’s 90% based on 2017’s closest perigee and farthest apogee
Espenak’s 90% based on perigee and apogee of each month’s orbit
November full moon’s distance relative to 2017’s closest perigee and farthest apogee
Astrophysicist Fred Espenak, aka Mr. Eclipse – a 30-year NASA veteran and world-renowned expert on eclipses – says the January 12, 2017 full moon is a supermoon in his post Moon in 2017.
Who are the commentators, and what do they say? The International Astronomical Union (IAU) is the group generally recognized for naming and defining things in astronomy. But the IAU has been, so far, silent on the subject of supermoons, which, professional astronomers tend to call perigean full moons.
Meanwhile, Fred Espenak, the go-to astronomer on all things related to lunar and solar eclipses (Mr. Eclipse!), lists the full moons of January, November and December 2017 as full moon supermoons in his great post, Moon in 2017.
We also need to consider the astrologer Richard Nolle. Whatever your thoughts or feelings are on astrology, Nolle is, after all, the person who coined the term supermoon. Of the 12 full moons that take place in 2017, he lists only the December full moon as a supermoon. The supermoon definition, as originally defined by Nolle, comes with ambiguity. That’s why there are different answers to the question of the number of supermoons in 2017.
Click here to learn more about Richard Nolle
Click here to learn more about Fred Espenak
We refer you to two different supermoon tables for the 21st century (2001 to 2100). Here is Richard Nolle’s table, and here is Fred Espenak’s table.
Richard Nolle lists only one full moon supermoon for 2017:
2017 December 3
Meanwhile, Fred Espenak lists three full moon supermoons in 2017:
2017 January 12
2017 November 4
2017 December 3
Why are their lists different?
Image via NASA
Original definition of supermoon. Supermoons are based on lunar perigee and apogee. Each month, the moon comes closest to Earth at perigee and swings farthest away at apogee.
In his original definition, Richard Nolle defined a supermoon as:
… a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit.
If a new or full moon aligns with apogee, then it’s at 0% of its closest approach to Earth. On the other hand, if a new or full moon aligns with perigee, then it’s at 100% of its closest approach to Earth. That’s something we can all agree on.
But the phrase 90% of perigee is ambiguous. Read on.
A 2013 supermoon, as captured by EarthSky Facebook Anthony Lynch in Dublin, Ireland.
Nolle’s 90% is based on 2017’s closest perigee and farthest apogee. Looking at Richard Nolle’s list for all the supermoons in the 21st century, it appears that Richard Nolle bases his 90% figure on the year’s closest perigee and farthest apogee. Take the year 2017, for instance, whereby any new or full moon coming closer than 362,146.6 km qualifies as a supermoon.
This year, in 2017, the moon comes closest to Earth on May 26 (357,207 kilometers) and swings farthest away toward the end of the year, on December 19 (406,603 kilometers). That’s a difference of 49,396 km (406,603 – 357,207 = 49,396 km). Ninety percent of this 49,396-figure equals 44,456.4 kilometers (0.9 x 49,396 = 44,456.4). Presumably, any new or full moon coming closer than 362,146.6 kilometers (406,603 – 44,456.4 = 362,146.6) would be “at or near (within 90% of) its closest approach to Earth.”
Farthest apogee (2017): 406,603 km
Closest perigee (2017): 357,207 km
Difference: 49,396 km
90% x 49,396 = 44,456.4 km
406,603 – 44,456.4 = 362,146.6 km = 90% of moon’s closest distance to Earth
Thus, figuring out “90% of the moon’s closest approach to Earth” by the year’s closest perigee and farthest apogee, any new or full moon swinging closer than 362,146.6 km to Earth in 2017 counts as a supermoon.
Since the full moon on November 4, 2017, only comes within 364,004 km of Earth, it doesn’t count as a supermoon on Richard Nolle’s list.
July 2014 supermoon via Evgeny Yorobe Photography
Espenak’s 90% based on perigee and apogee of each month’s orbit. Ironically, Fred Espenak’s full supermoon list might more strictly adhere to Richard Nolle’s definition (at least as it is written) than Richard Nolle himself does.
Once again, Richard Nolle describes a supermoon as:
… a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.
If given orbit can be taken to mean current monthly orbit, then the November 2017 full moon comes to within 94.1% of its closest approach to Earth relative to the most recent perigee and the upcoming apogee.
October 25, 2017 apogee: 405,151 km
November 6, 2017 perigee: 361,438 km
Difference: 43,713 km
October 25, 2017 apogee: 405,151 km
November 4, 2017 full moon: 364,004 km
Difference: 41,147 km
41,147/43,713 = 0.941 (94.1%) = distance of the November 2017 full moon relative to the most recent perigee and upcoming apogee
Depending on what meaning we give to the words in a given orbit, we could say the October 25 apogee = 0% of the moon’s closest approach to Earth for this orbit, and the November 6 perigee = 100% of the moon’s closest approach to Earth.
That being the case, then the November full moon comes to within 94.1% of its closest approach to Earth for the month: 41,147/43,713 = 0.941 = 94.1%
Super cool super-moonrise composite from Fiona M. Donnelly in Ontario. This photo is from the August 2014 supermoon.
November full moon’s distance relative to 2017’s closest perigee/farthest apogee. However, if we compute the percentage distance of the November full moon relative to the year’s farthest apogee and closest perigee, then the November full moon only comes to within 86.2% of its closest approach to Earth:
Farthest apogee (2017): 406,603 km
Closest perigee (2017): 357,207 km
Difference: 49,396 km
Farthest apogee (2017): 406,603 km
November full moon (2017): 364,004 km
Difference: 42,599 km
42,599/49,396 = 0.862 (86.2%) = distance of the November full moon relative to the year’s farthest apogee and closest perigee
Another contrast of a full supermoon (full moon at perigee) with a micro-moon (full moon at apogee). Image credit: Stefano Sciarpetti
Is the November full moon a supermoon? Depends on which perigee/apogee distances you choose. The moon’s perigee and apogee distances vary throughout the year, so it appears that the limiting distance for the supermoon depends on which perigee and apogee distances are being used to compute 90% of the moon’s closest approach to Earth.
If we choose the year’s closest perigee and farthest apogee, as Nolle did, we narrow the definition of supermoon.
If we choose the perigee and apogee for a given monthly orbit, as Espenak did, then we broaden the definition of supermoon.
Given the narrower definition, the full moon on November 4, 2017, is not a supermoon, but given the broader one, it is.
Take your choice!
The moon’s apparent size in our sky depends on its distance from Earth. The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Image by Marco Langbroek of the Netherlands via Wikimedia Commons.
Bottom line: At least two commentators – Richard Nolle and Fred Espenak – disagree on whether the November 4, 2017, full moon should be called a supermoon. Is it? If you define a supermoon based on the year’s closest perigee and farthest apogee, then the November 2017 full moon is not a supermoon. If you define a supermoon based on the perigee and apogee for a given monthly orbit, then it is a supermoon. Take your choice!
from EarthSky http://ift.tt/2iK8qd3
Apparent size of a full supermoon, or close moon, contrasted with a full micro-moon, or far moon. Image by Peter Lowenstein.
The 11th of 2017’s 12 full moons falls on November 3-4; click here to learn the exact time of full moon. This full moon ranks as the second-closest one of 2017, but it’s less than clear whether it should be dubbed a supermoon, mainly because people disagree on what constitutes a supermoon. Follow the links below to learn more.
Who are the commentators, and what do they say?
Original definition of supermoon
Nolle’s 90% based on 2017’s closest perigee and farthest apogee
Espenak’s 90% based on perigee and apogee of each month’s orbit
November full moon’s distance relative to 2017’s closest perigee and farthest apogee
Astrophysicist Fred Espenak, aka Mr. Eclipse – a 30-year NASA veteran and world-renowned expert on eclipses – says the January 12, 2017 full moon is a supermoon in his post Moon in 2017.
Who are the commentators, and what do they say? The International Astronomical Union (IAU) is the group generally recognized for naming and defining things in astronomy. But the IAU has been, so far, silent on the subject of supermoons, which, professional astronomers tend to call perigean full moons.
Meanwhile, Fred Espenak, the go-to astronomer on all things related to lunar and solar eclipses (Mr. Eclipse!), lists the full moons of January, November and December 2017 as full moon supermoons in his great post, Moon in 2017.
We also need to consider the astrologer Richard Nolle. Whatever your thoughts or feelings are on astrology, Nolle is, after all, the person who coined the term supermoon. Of the 12 full moons that take place in 2017, he lists only the December full moon as a supermoon. The supermoon definition, as originally defined by Nolle, comes with ambiguity. That’s why there are different answers to the question of the number of supermoons in 2017.
Click here to learn more about Richard Nolle
Click here to learn more about Fred Espenak
We refer you to two different supermoon tables for the 21st century (2001 to 2100). Here is Richard Nolle’s table, and here is Fred Espenak’s table.
Richard Nolle lists only one full moon supermoon for 2017:
2017 December 3
Meanwhile, Fred Espenak lists three full moon supermoons in 2017:
2017 January 12
2017 November 4
2017 December 3
Why are their lists different?
Image via NASA
Original definition of supermoon. Supermoons are based on lunar perigee and apogee. Each month, the moon comes closest to Earth at perigee and swings farthest away at apogee.
In his original definition, Richard Nolle defined a supermoon as:
… a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit.
If a new or full moon aligns with apogee, then it’s at 0% of its closest approach to Earth. On the other hand, if a new or full moon aligns with perigee, then it’s at 100% of its closest approach to Earth. That’s something we can all agree on.
But the phrase 90% of perigee is ambiguous. Read on.
A 2013 supermoon, as captured by EarthSky Facebook Anthony Lynch in Dublin, Ireland.
Nolle’s 90% is based on 2017’s closest perigee and farthest apogee. Looking at Richard Nolle’s list for all the supermoons in the 21st century, it appears that Richard Nolle bases his 90% figure on the year’s closest perigee and farthest apogee. Take the year 2017, for instance, whereby any new or full moon coming closer than 362,146.6 km qualifies as a supermoon.
This year, in 2017, the moon comes closest to Earth on May 26 (357,207 kilometers) and swings farthest away toward the end of the year, on December 19 (406,603 kilometers). That’s a difference of 49,396 km (406,603 – 357,207 = 49,396 km). Ninety percent of this 49,396-figure equals 44,456.4 kilometers (0.9 x 49,396 = 44,456.4). Presumably, any new or full moon coming closer than 362,146.6 kilometers (406,603 – 44,456.4 = 362,146.6) would be “at or near (within 90% of) its closest approach to Earth.”
Farthest apogee (2017): 406,603 km
Closest perigee (2017): 357,207 km
Difference: 49,396 km
90% x 49,396 = 44,456.4 km
406,603 – 44,456.4 = 362,146.6 km = 90% of moon’s closest distance to Earth
Thus, figuring out “90% of the moon’s closest approach to Earth” by the year’s closest perigee and farthest apogee, any new or full moon swinging closer than 362,146.6 km to Earth in 2017 counts as a supermoon.
Since the full moon on November 4, 2017, only comes within 364,004 km of Earth, it doesn’t count as a supermoon on Richard Nolle’s list.
July 2014 supermoon via Evgeny Yorobe Photography
Espenak’s 90% based on perigee and apogee of each month’s orbit. Ironically, Fred Espenak’s full supermoon list might more strictly adhere to Richard Nolle’s definition (at least as it is written) than Richard Nolle himself does.
Once again, Richard Nolle describes a supermoon as:
… a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.
If given orbit can be taken to mean current monthly orbit, then the November 2017 full moon comes to within 94.1% of its closest approach to Earth relative to the most recent perigee and the upcoming apogee.
October 25, 2017 apogee: 405,151 km
November 6, 2017 perigee: 361,438 km
Difference: 43,713 km
October 25, 2017 apogee: 405,151 km
November 4, 2017 full moon: 364,004 km
Difference: 41,147 km
41,147/43,713 = 0.941 (94.1%) = distance of the November 2017 full moon relative to the most recent perigee and upcoming apogee
Depending on what meaning we give to the words in a given orbit, we could say the October 25 apogee = 0% of the moon’s closest approach to Earth for this orbit, and the November 6 perigee = 100% of the moon’s closest approach to Earth.
That being the case, then the November full moon comes to within 94.1% of its closest approach to Earth for the month: 41,147/43,713 = 0.941 = 94.1%
Super cool super-moonrise composite from Fiona M. Donnelly in Ontario. This photo is from the August 2014 supermoon.
November full moon’s distance relative to 2017’s closest perigee/farthest apogee. However, if we compute the percentage distance of the November full moon relative to the year’s farthest apogee and closest perigee, then the November full moon only comes to within 86.2% of its closest approach to Earth:
Farthest apogee (2017): 406,603 km
Closest perigee (2017): 357,207 km
Difference: 49,396 km
Farthest apogee (2017): 406,603 km
November full moon (2017): 364,004 km
Difference: 42,599 km
42,599/49,396 = 0.862 (86.2%) = distance of the November full moon relative to the year’s farthest apogee and closest perigee
Another contrast of a full supermoon (full moon at perigee) with a micro-moon (full moon at apogee). Image credit: Stefano Sciarpetti
Is the November full moon a supermoon? Depends on which perigee/apogee distances you choose. The moon’s perigee and apogee distances vary throughout the year, so it appears that the limiting distance for the supermoon depends on which perigee and apogee distances are being used to compute 90% of the moon’s closest approach to Earth.
If we choose the year’s closest perigee and farthest apogee, as Nolle did, we narrow the definition of supermoon.
If we choose the perigee and apogee for a given monthly orbit, as Espenak did, then we broaden the definition of supermoon.
Given the narrower definition, the full moon on November 4, 2017, is not a supermoon, but given the broader one, it is.
Take your choice!
The moon’s apparent size in our sky depends on its distance from Earth. The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Image by Marco Langbroek of the Netherlands via Wikimedia Commons.
Bottom line: At least two commentators – Richard Nolle and Fred Espenak – disagree on whether the November 4, 2017, full moon should be called a supermoon. Is it? If you define a supermoon based on the year’s closest perigee and farthest apogee, then the November 2017 full moon is not a supermoon. If you define a supermoon based on the perigee and apogee for a given monthly orbit, then it is a supermoon. Take your choice!
from EarthSky http://ift.tt/2iK8qd3
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