|Home Page||Astronomy Articles||Stars Page||Astronomy Links|
|Vis-Viva Along with the Lyrid Meteor Shower|
|& the March 2011 "SuperMoon" Revisted|
Vis-Viva With the Lyrid Meteors
Yes, you can calculate the speed the April Lyrid meteors with relative ease. This annual meteor shower peaks around April 22 or 23, and is usually a modest shower, producing the greatest number of Lyrids in the dark hour before dawn (perhaps 10 to 15 per hour). This year, in 2011, the Lyrid shower will have to contend with the light of the waning gibbous moon.
Meteor showers result when the Earth in its orbit passes through the orbital path of a comet, and the cometary debris burns up in Earth's atmosphere as streaking meteors. In the case of the Lyrids, the Earth crosses the orbit of Comet Thatcher.
Velocity of the Lyrid Meteoroid Stream
Once we know the semi-major axis of Comet Thatcher's orbit in astronomical units, we have all we need to figure out how fast the particles in the Lyrid meteoroid stream travel through space at the Earth's distance from the Sun. (By the way, the particles are called meteoroids when traveling in outer space and meteors when burning up in the Earth's atmosphere.) According to this site, the semi-major axis = 55.68 astronomical units. In astronomy, the letter a is used as a symbol for the semi-major axis.
Enter the Vis-Viva Equation
All you have to do is to substitute 55.68 for a in the equation below to know how fast the Lyrid meteoroids travel in miles per hour through space at the Earth's distance from the Sun:
|Velocity = 66,627 x the square root of (2-1/a)|
|Velocity = 66,627 x the square root of (2-1/55.68)|
|Velocity = 66,627 x the square root of (2-0.01796)|
|Velocity = 66,627 x the square root of 1.98204|
|Velocity = 66,627 x 1.40785 = 93,801 miles per hour|
Want more? Try calculating the velocity of the Perseids. The semi-major axis for Comet Swift-Tuttle, the parent of the Perseid shower, is 26.092 astronomical units. Click here for the answer.
The 2011 March 19 "SuperMoon" Revisited
The catchy term "SuperMoon" spread like wildfire in media reports of the year's closest Full Moon on March 19, 2011. Even NASA and National Geographic got on the bandwagon, using a newfangled word that has more gravitas than definition.
Apparently, the astrologer Richard Nolle coined the term SuperMoon to describe any Full Moon or New Moon that comes within 90% of its closest approach in a given orbit. In the course of one month, the moon's distance from Earth varies by about 50,000 kilometers (30,000 miles). Its closest point to Earth is called perigee and its farthest point is called apogee. Ninety percent of 50,000 km is 45,000 km. So, by this definition, any Full Moon or New Moon coming within 5,000 kilometers of the perigee distance qualifies as a "Super" New Moon or "Super" Full Moon. (Photo Credit: bilboard99)
What Definition Does NASA Have In Mind?
In this NASA write-up, it's said that the Full Moon on December 12, 2008 was almost a SuperMoon. Why it doesn't make the grade is left to one's imagination, as Richard Nolle lists the Full Moon of 2008 December 12 as a SuperMoon on his SuperMoon Table. In fact, there are SuperMoons every year, anywhere from 3 to 6 SuperMoons, depending on the year.
The same NASA article also states, "The full Moon of March 19th occurs less than one hour away from perigee - a near-perfect coincidence that happens only 18 years or so." I was beginning to wonder about the validity of the claim when seeing the Full Moon perigees on the following dates on this perigee calculator: January 19, 1992; May 6, 2012; June 23, 2013; and August 10, 2014. However, if I allow for the possibility of close-knit Full Moon perigees for a few years in succession, the statement may have something to it after all.
SuperMoons of 1955, 1974, 1992 and 2005?
This article quotes Mark Paquette: "These years had their share of extreme weather and other natural events. Is the supermoon and these natural occurrences a coincidence?" Given that SuperMoons (as defined by Richard Nolle) happen several times every year, it was hard for me to fathom why 1955, 1974, 1992 and 2005 should be all that significant. The spacing looks suspiciously close to the purported approximate 18-year cycle, except that there is about a 3-hour difference between Full Moon and perigee on December 29, 1955. On January 10, 2005, the closest perigee coincides with the New Moon.
Moon's Closest Encounter With Earth Since 1993?
No! March 19, 2011 presented the Moon at its closest since December 12, 2008. At perigee on March 19, 2011, the Moon was 356,575 kilometers from Earth. At perigee on December 12, 2008, the Moon was slightly closer, at 356,566 kilometers away. Although the Full Moon and perigee fall on or near the same date every 413 days, the number of hours between the two events varies - depending on the year.
Closest Full Moon Since 1993?
Yes. If we choose to give the distances at the instant of Full Moon, then the Full Moon of March 19, 2011 was slightly closer than the Full Moon of December 12, 2008. Astronomically speaking, the Moon is full at that fleeting moment when it resides 180 degrees from the Sun in ecliptic (or celestial) longitude.
In years when the Full Moon perigee is not the closest perigee of the year, it's the New Moon perigee that is. New Moon perigees occur midway between Full Moon perigees, and vice versa. The New Moon, like the Full Moon, realigns with perigee every 413 days, or in a time period of about 1 year 1 month and 18 days.
copyright 2011 by Bruce McClure
|Lunar Perigee and Apogee Calculator|
March 2011 Feature * May 2011 Feature