by Chris Peterson » Thu Nov 22, 2012 3:37 pm
Ron wrote:How do we know these are grain of sand size, and not golf ball size or watermelon size. ?
There is a well established relationship between the intensity profile of a meteor and the mass of the meteoroid. In addition, Leonids and other meteor showers are well characterized by radar.
The meteoroid that produced the fireball in today's image was certainly
not the size of a grain of sand, however! While a typical Leonid meteor is one or two millimeters across, a fireball like this is probably a centimeter or larger- a marble, not a piece of sand.
On another track, do these ever dive straight down into the atmosphere, rather than streak across the sky. Does that produce a different type of track - or photo ?
All of the meteoroids are moving parallel to one another, in a zone larger than the diameter of the Earth. The angle of an individual meteor in the atmosphere is determined by where it strikes- if it is in the center of Earth's path through the field, the path will be directly down toward the ground; if it nearly misses the planet completely, it will be an Earth-grazer like that in the image, moving parallel to the ground. When you are observing a meteor shower, meteors close to the radiant are moving towards you, and typically are short. As you see meteors farther from the radiant, they are traveling more obliquely with respect to the observer, and tend to have longer paths. If you view when the radiant is overhead, meteors near the radiant are heading almost straight towards the ground, while meteors near the horizons are almost parallel to the ground.
[quote="Ron"]How do we know these are grain of sand size, and not golf ball size or watermelon size. ?[/quote]
There is a well established relationship between the intensity profile of a meteor and the mass of the meteoroid. In addition, Leonids and other meteor showers are well characterized by radar.
The meteoroid that produced the fireball in today's image was certainly [i]not [/i]the size of a grain of sand, however! While a typical Leonid meteor is one or two millimeters across, a fireball like this is probably a centimeter or larger- a marble, not a piece of sand.
[quote]On another track, do these ever dive straight down into the atmosphere, rather than streak across the sky. Does that produce a different type of track - or photo ?[/quote]
All of the meteoroids are moving parallel to one another, in a zone larger than the diameter of the Earth. The angle of an individual meteor in the atmosphere is determined by where it strikes- if it is in the center of Earth's path through the field, the path will be directly down toward the ground; if it nearly misses the planet completely, it will be an Earth-grazer like that in the image, moving parallel to the ground. When you are observing a meteor shower, meteors close to the radiant are moving towards you, and typically are short. As you see meteors farther from the radiant, they are traveling more obliquely with respect to the observer, and tend to have longer paths. If you view when the radiant is overhead, meteors near the radiant are heading almost straight towards the ground, while meteors near the horizons are almost parallel to the ground.