Comets

A comet's tail always points away from the Sun, so it may be in front of the comet as the comet travels away from the Sun.

A comet's tail always points away from the Sun, so it may be in front of the comet as the comet travels away from the Sun.

ion tail

A stream of ionized particles evaporated from a comet and then swept away from the Sun by the solar wind.

A typical short-period comet might return to the inner Solar System after 150 years. (Reason: Short-period comets have orbital periods of less than 200 years).

A typical short-period comet might return to the inner Solar System after 150 years. (Reason: Short-period comets have orbital periods of less than 200 years).

Oort Cloud

A vast region in which comet nuclei orbit. This cloud lies far beyond the orbit of Pluto and may extend halfway to the next nearest star.

As a comet approaches the Sun, solar radiation causes ices on comet's surface to sublimate (The ices turn directly into gas

As a comet approaches the Sun, solar radiation causes ices on comet's surface to sublimate (The ices turn directly into gas

How would a comet nucleus be best described?

As a dirty snowball, loosely packed (Current estimates of the densities of comet nuclei are less than 1 kg/L. They appear to be loosely packed, at least for a good chunk of the volume, rather than solid ice).

Comets are leftover material, a mix of ice and dust, from the formation of the Solar System.

Comets are leftover material, a mix of ice and dust, from the formation of the Solar System.

Comets from the Oort cloud might develop elliptical orbits and arrive in the inner Solar System as a result of gravitational interactions with other nearby stars in the Milky Way and dwarf planets that orbit in the Oort cloud

Comets from the Oort cloud might develop elliptical orbits and arrive in the inner Solar System as a result of gravitational interactions with other nearby stars in the Milky Way and dwarf planets that orbit in the Oort cloud

Compared to the Kuiper belt, the Oort cloud is... · about 2000 times farther from the Sun (reason: The Oort cloud is at about 100,000 AU.) · more nearly spherical · colde

Compared to the Kuiper belt, the Oort cloud is... · about 2000 times farther from the Sun (reason: The Oort cloud is at about 100,000 AU.) · more nearly spherical · colde

Dust lost from a comet continues in orbit and can create meteor showers if Earth passes through the debris cloud

Dust lost from a comet continues in orbit and can create meteor showers if Earth passes through the debris cloud

Each time a comet passes by the Sun, it loses the material that forms the tail, parts of the nucleus experience outbursts, explosions, and melting

Each time a comet passes by the Sun, it loses the material that forms the tail, parts of the nucleus experience outbursts, explosions, and melting

If the comet's orbit brings it to the inner Solar System, the solar wind pulls gas from the coma into an ion tail, and radiation pressure from the Sun pushes the dust particles out into a dust tail.

If the comet's orbit brings it to the inner Solar System, the solar wind pulls gas from the coma into an ion tail, and radiation pressure from the Sun pushes the dust particles out into a dust tail.

Ion tails of comets glow through fluorescence. The process is also why fluorescent paint looks bright at twilight or under a blacklight. It happens when ultraviolet photons excite electrons in atoms to high-energy orbitals. The electrons emit multiple lower-energy photons as they drop back down (Reason: In fluorescence, the electrons are excited by external radiation).

Ion tails of comets glow through fluorescence. The process is also why fluorescent paint looks bright at twilight or under a blacklight. It happens when ultraviolet photons excite electrons in atoms to high-energy orbitals. The electrons emit multiple lower-energy photons as they drop back down (Reason: In fluorescence, the electrons are excited by external radiation).

It is possible that material in the Oort cloud originated closer in and was sent outward by gravitational interactions with the Jovian planets

It is possible that material in the Oort cloud originated closer in and was sent outward by gravitational interactions with the Jovian planets

Long-period comets come from the Oort Cloud, which extends roughly 100,000 AU from the Sun.

Long-period comets come from the Oort Cloud, which extends roughly 100,000 AU from the Sun.

Short-period comets have orbits less than 200 years long and generally originate from Kuiper belt.

Short-period comets have orbits less than 200 years long and generally originate from Kuiper belt.

Shower meteors seem to come from one point on the sky, the radiant, because the shower is caused by the Earth running into a concentration of debris. (Reason: The meteors come from debris along a comet's orbit. The Earth crosses the orbit, so the meteors all contact the atmosphere from the same direction).

Shower meteors seem to come from one point on the sky, the radiant, because the shower is caused by the Earth running into a concentration of debris. (Reason: The meteors come from debris along a comet's orbit. The Earth crosses the orbit, so the meteors all contact the atmosphere from the same direction).

The Kuiper belt is the source of short-period comets. It also contains many times more mass than the asteroid belt, has objects with orbits of varied inclinations but that are fairly close to the plane of the Solar System, and is home to the TNOs in addition to other icy bodies

The Kuiper belt is the source of short-period comets. It also contains many times more mass than the asteroid belt, has objects with orbits of varied inclinations but that are fairly close to the plane of the Solar System, and is home to the TNOs in addition to other icy bodies

The Sun plays a role in creating both tails of a comet. Radiationpressure from sunlight pushes particles out of the coma to form the dust tail of a comet, but the ion tail is shaped by the solar wind

The Sun plays a role in creating both tails of a comet. Radiationpressure from sunlight pushes particles out of the coma to form the dust tail of a comet, but the ion tail is shaped by the solar wind

the process of fluorescence

The gases in the tail absorb ultraviolet light from the Sun. · The energy from an ultraviolet photon lifts an electron bound to a gas atom up several energy levels · The electron spontaneously drops back down, stopping at an intermediate level and emitting a lower energy visible light photon. The electron takes additional steps back down, emitting additional visible or lower-energy light rays until it is back to where it started.

The meteor shower appears to come from the direction of a comet's orbit relative to Earth's own motion

The meteor shower appears to come from the direction of a comet's orbit relative to Earth's own motion

The object Oumaumau passed inside the orbit of Mercury in September 2017 and showed evidence of acceleration in its trajectory. It is small, shows variations in brightness, and was traveling very fast compared to the typical Solar System object. Based on this evidence astronomers believe it might be a comet from outside our Solar System

The object Oumaumau astronomers believe it might be a comet from outside our Solar System because evidence of acceleration in its trajectory. It is small, shows variations in brightness, and was traveling very fast compared to the typical Solar System object. It was traveling too fast to have come from the Oort cloud.

They are basically "dirty snowballs" that spend most of their time far from the Sun at temperatures close to absolute zero.

They are basically "dirty snowballs" that spend most of their time far from the Sun at temperatures close to absolute zero.

What usually happens when small rocks or chunks of ice enter Earth's atmosphere? Friction with the atmosphere heats them, causing a "shooting star" to appear

What usually happens when small rocks or chunks of ice enter Earth's atmosphere? Friction with the atmosphere heats them, causing a "shooting star" to appear

When a comet gets too near the Sun, ices sublimate and carry off dust particles, forming a gas cloud (coma) around the nucleus

When a comet gets too near the Sun, ices sublimate and carry off dust particles, forming a gas cloud (coma) around the nucleus

Where would you find a comet that has a long tail? · At the orbit of Earth · Inside the orbit of Mercury

Where would you find a comet that has a long tail? · At the orbit of Earth · Inside the orbit of Mercury

dust tail

a comet tail containing dust that reflects sunlight. The dust in a comet tail is expelled from the nucleus of the comet.

Halley's comet

a comet that reappears about every 76 years, famous because it was the first comet whose return was predicted

Long-period comet

a comet whose orbital period is longer than 200 years. these comets may originates from the Oort Cloud.

short-period comet

a comet whose orbital period is shorter than 200 years. For example, Halley's Comet has a period of 76 years.

Kuiper Belt

a region containing many large icy bodies and from which some comets come. The region appears to extend from the orbit of Neptune at about 30 AU, past Pluto, out to approximately 55 AU.

meteor shower

an event in which many meteors occur in a short space of time, all from the same general direction in the sky, typically when Earth's orbit intersects debris left by a comet. The most famous shower is the Perseids in mid-August.

meteor

the brighter trail of light created by small solid particles entering Earth's atmosphere and burning up; a shooting star

fluorescence

the conversion of ultraviolet light (or other short-wavelength radiation) into visible light. This occurs, for example, when an atom is excited into a high energy level by an ultraviolet photon, and then descends to the ground state in a series of steps, emitting lower-energy photons.

nucleus

the core of an atom around which its electrons orbit. The nucleus has a positive electric charge and comprises most of an atom's mass

radiation pressure

the force exerted by photons when they strike matter

coma

the gaseous atmosphere surrounding the head of a comet

solar wind

the outflow of low-density, hot gas from the Sun's upper atmosphere. It is partially this wind that creates the tail of a comet by pushing a comet's gases away from the Sun.

radiant

the point in the sky from which meteors in showers appear to originate. See also meteor shower

sublimate

to charge directly from a solid into a gas without passing through a liquid phase

Math the parts of a comet to their approximate sizes: gas and dust tails, hydrogen envelope, coma, and nucleus.

· 10 km - nucleus · 100 million km - gas and dust tails · 100,000 km - coma · 10 million km - hydrogen envelope

· Perseids - August meteor shower associated with comet Swift-Tuttle · Meteor - Particle of asteroid or comet burning up in the atmosphere · Radiant - Point on the sky from which meteors in the shower seem to diverge · Meteor shower - Many meteors associated with particular debris in the Earth's path hitting the atmosphere over a few hours. · Geminids - A shower in December with many meteors per hour

· Perseids - August meteor shower associated with comet Swift-Tuttle · Meteor - Particle of asteroid or comet burning up in the atmosphere · Radiant - Point on the sky from which meteors in the shower seem to diverge · Meteor shower - Many meteors associated with particular debris in the Earth's path hitting the atmosphere over a few hours. · Geminids - A shower in December with many meteors per hour

What is the source of materials for a comet's tail?

· Sublimated (evaporated) material from the nucleus (Sublimation is changing directly from solid to gas. It is what happens to some of the ices in a comet's nucleus as it comes close to the Sun. The gas and dust freed from the nucleus make the comet's tail.)