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<\/a>Helion and Anthelion<\/h3>\n\n\n\n
Firstly we have the Helion and Anthelion, which are respectively, the points directly toward and away from the Sun and account for around 20-40% of Sporadics. Helion and Anthelion meteors are orbiting the sun in the plane of the Ecliptic in the same direction as the Earth, and Anthelion meteors encounter the Earth on their way inwards towards the Sun. They’re typically therefore moving at about 30 km\/s relative to the Earth. The Anthelion “radiant” is a broad area centred on the point 165 degrees west of the Sun and is shifted from the point exactly opposite due to the Earth’s orbital motion. The Helion radiant is about 15 degrees from the Sun and so for visual and photographic observers the Helion can be ignored.<\/p>\n\n\n\n
The source of these meteors is believed to be debris from Jupiter-family comets and small asteroids most of which broke up long ago. If you look in extended meteor shower catalogues, you will find many weak showers whose radiant lies within the broad area classed as the Anthelion. <\/p>\n\n\n\n
Toroidal Regions<\/h3>\n\n\n\n
The next two areas which provide concentrations of Sporadics are the Toroidal regions. These correspond to dust with highly inclined orbits centred on 67 degrees tilt. Because of their orbits, they’re difficult to study visually and some researchers have questioned whether the sources even exist. Analysis in the early 2010s suggested that after removal of observational bias, only 3-6% of Sporadics could be classified as Toroidal and some researchers believe they’re actually just scattered dust from the Helion and Anthelon sources.<\/p>\n\n\n\n
Apex Regions<\/h3>\n\n\n\n
Finally we have the Northern and Southern Apex sources which account for about 25-30% of Sporadics. The Apex is the point in space towards which the Earth appears to be moving as it orbits round the Sun and these meteors are caused by dust moving in a retrograde orbit, that is to say orbiting in the the opposite direction to the Earth. The two sources ar about 15 degrees above and below the Ecliptic, and at 90 degrees away from the sun. The gap between them is thought to be due to the Earth clearing its orbit of debris. <\/p>\n\n\n\n
Because we encouter Apex meteors head-on and moving in the opposite direction, they generally have very high velocities and can form bright long-lasting trails, though they’ll be foreshortened near the apparent radiant. Apex meteors are best seen just before dawn because the radiant doesn’t rise till then. <\/p>\n\n\n\n
How Frequent Are They?<\/h2>\n\n\n\n
All the sporadic sources together contribute maybe 5 meteors per hour over the whole sky, but over time that adds up. On a clear winter’s night a modern video detection system might pick up 20-30 sporadics per night. <\/p>\n\n\n\n
Could They Actually be Showers?<\/h2>\n\n\n\n
Shower meteors are identified by looking for common velocity and pre-atmospheric trajectory characteristics that correspond to having approximately the same orbit round the Sun, and which therefore are likely to have come from the same parent body. Sometimes, we can identify the source (eg 2P\/Encke for the Taurids) because it also has a similar orbit. Sometimes, we can’t identify the parent body. This could mean it was a comet that has since disintegrated completely, or it could be that the parent has been perturbed out of its original orbit, etc.<\/p>\n\n\n\n
Sporadics don’t really show the same sort of clustering. Although they come generally from the same area and have the same sort of velocity, the apparent radiant area is much larger. To be classed as a shower, meteors must come from a small area typically nor more than 5-10 degrees diameter, and have velocities within a few km\/s of each other. The Sporadic radiants discussed above are 9-10x larger in area, and the range of velocities is much larger. <\/p>\n\n\n\n
That said, within the area covered by the Anthelion and Apex, there are also quite a few named showers, as you can see from the image. Some of these are of questionable quality as the next section explains. <\/p>\n\n\n\n
Ok, but there could still be Undiscovered Showers<\/h2>\n\n\n\n
Yes, sure. There are doubtless weak undiscovered showers and a few are proposed each year. GMN data was used to identify a new shower about 12 months ago. However, over the centuries, most obvious clusterings have been mapped and most sporadics are probably just general space dust, bits of junk left over from the formation of the solar system or formed by collisions in the asteroid belt or elsewhere.<\/p>\n\n\n\n
There are also many showers that overlap in time and space, leading to challenges as to whether they’re truly distinct showers or different streams in the same larger shower. As you may know, the radiant of a shower drifts from day to day due to the orbital motions of the bodies involved, and if there’s a gap in the dust, then it might appear to be two showers. Also sometimes dust streams split into two forming two distinct outbursts. These can end up being classed as two showers (eg northern and southern taurids) if the apparent radiants are distinct enough, even though they are part of the same debris stream.<\/p>\n\n\n\n
Its been the case in the past that teams have inadvertently rediscovered an existing shower and given it a new name, or have made a discovery claim that other researchers can’t confirm, or have published a claimed discovery in the popular press before getting it confirmed etc. <\/p>\n\n\n\n
Identification of a new shower can therefore be contentious, and should be done rigorously, with proper peer review and confirmation from independent researchers.
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The majority of meteors are sporadics. Sporadics are pieces of space dust which are not associated with any known meteor shower and in 2022 60% of confirmed meteors in the UKMON dataset were sporadics. The picture below shows all theRead more<\/span><\/a><\/p>\n","protected":false},"author":23,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[],"tags":[],"class_list":["post-4349","page","type-page","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t