Astronomy Chapter on Asteroids and Spectra

Observing the Local Sky

• Stars, planets, and the moon are visible to the naked eye at night.
• People of various cultures named star patterns as constellations.
• Early astronomers used constellations for navigation and calendars.
• Today's astronomers use constellations to define large areas of the sky.
• The apparent movement of constellations across the sky is due to Earth's rotation.
• Stars appear to be firmly attached to a celestial sphere surrounding Earth, but this is an illusion.
• Stars' actual distances can vary greatly within a constellation.
• The celestial sphere lets us visualize the position of stars.

Circling the Sky

• The sky appears to change as Earth rotates
• We view the local sky from a specific location.
• Angles are used to locate objects in the local sky.
• Altitude and azimuth are two angles needed to locate any object.
• Altitude represents elevation, and azimuth is direction.
• The meridian is an imaginary half-circle extending from North through Zenith to South.
• The horizon is where the sky meets the Earth.

Celestial Coordinate System

• The local sky can be extended to encompass the entire Earth.
• The altitude-azimuth system can describe any object in the local sky's coordinates.
• The geographical coordinates (latitude and longitude) provide the location on Earth.

Motion of Objects in the Sky

• The sky changes during the day.
• Stars move in a circular or semi-circular path.
• Circumpolar stars never rise or set.
• Non-circumpolar stars rise in the east and set in the west.
• Paths of the sun, moon, and planets follow the rules of sky motion.

The Reason for Seasons

• The sun's apparent path across the sky varies throughout the year, due to the Earth's tilt.
• The Earth's tilted axis and orbit around the Sun create the seasons.
• Solstices and equinoxes mark the maximum and minimum heights of the Sun.

The Precession of Earth's Axis

• Earth's axis of rotation slowly changes its orientation over a period of ~26,000 years
• It is caused by gravitational forces from the Sun and Moon.

The Moon: Our Constant Companion

• The moon orbits the Earth.
• We see different portions of the moon illuminated by the sun (phases).
• The moon's phases are due to its position relative to the Earth and Sun.
• The relative orbital motions of the Earth/Moon/Sun cause eclipses.

Solar Eclipses and Celestial Timekeeping

• Solar eclipses occur when the Moon passes between the Sun and Earth, casting a shadow on Earth.
• Synodic and sidereal periods are used to measure the Moon's orbit.
• A solar day is defined by the position of the Sun, while a sidereal day is measured relative to a distant star.
• Earth's period of rotation (sidereal day) is slightly shorter than its orbital period (solar day).

Electromagnetic Radiation

• Electromagnetic energy is transferred through space without any physical movement.
• The EM spectrum includes visible light, radio waves, infrared, and ultraviolet waves, among others.
• Properties of objects emit EM radiation that can be measured and analyzed to determine their nature.
• Some properties of light include wavelength, frequency, color, and other characteristics.

Light and Its Properties

• Light is a form of electromagnetic radiation.
• Light waves consist of oscillating electric and magnetic fields.
• Light can be described using wavelengths and frequencies.
• Light's properties are determined by the wavelength.
• The visible spectrum of light contains all the colors that are visible to human eyes.
• Other properties include the frequency and wave intensity of the light.

Charged Particles

• Charged particles have mass and electric charge.
• Electrons and protons are fundamental particles of atoms.
• These fundamental particles carry the basic unit of electric charge.

Transmission of Electric Force

• Electric fields and magnetic fields are linked.
• Moving charges create magnetic fields.
• Variations in the electric field carry information from a distant source.

Thermal Radiation

• All objects emit radiation at all temperatures.
• The amount and types of radiation depend on the temperature of the object.
• A black body is a hypothetical object that absorbs all incoming radiation.
• The amount and types of emitted radiation can characterize the material, properties and temperature of an object.

Doppler Effect

• The Doppler effect describes the change in wave frequency emitted by a moving source.
• When a source is moving relative to an observer, the apparent wavelength changes.
• This effect is useful in astronomy for measuring the motion of celestial objects.

Spectroscopy

• Spectroscopy is the study of the interaction of light with matter.
• It involves using instruments to split light into its component wavelengths (colors).
• The spectrum of an object reveals information about its physical state, chemical composition, and temperature.

Atomic Structure

• Atoms consist of a nucleus surrounded by electrons.
• Energy levels of electrons determine the spectrum of emitted lights (color).

Telescopes

• Telescopes collect light from distant objects.
• Types of telescopes include refracting (lenses) and reflecting (mirrors).
• Refracting telescopes use lenses to bend light.
• Reflecting telescopes use mirrors to focus light.
• Factors like size, aperture, and optical type influence a telescope.

Resolution of Telescopes

• Resolution refers to the ability of a telescope to distinguish objects that appear close together.
• Factors such as telescope size, light wavelength, and atmospheric conditions affect resolution.

High Resolution Observation

• The atmosphere can blur images of distant objects.
• To compensate for atmospheric blurring, adaptive optics adjusts telescope mirrors in real time
• The resolving power of a telescope is dependent on wavelength and size.

Radio Astronomy

• Radio waves are a form of electromagnetic radiation.
• Radio telescopes use antennas instead of reflecting mirrors to detect radiation.
• Radio waves penetrate the atmosphere, and observations can be made 24 hours a day, regardless of the weather

Inner Planets

• The inner planets are composed primarily of rocks, metals, and silicates.
• They are relatively small compared to the outer planets.
• They have few moons, if any.
• They have relatively high densities.

Jovian Planets

• Jovian planets are composed primarily of hydrogen, helium, and other gases.
• These planets are relatively large compared to the inner planets.
• They have many moons.
• They have low densities.

Summary of the Solar System

• The solar system consists of the Sun, planets, moons, asteroids, and other small bodies.
• The planets orbit the Sun in approximately the same plane, and they orbit in the same direction.
• Their relative distances from the Sun vary.

Main Structure of the Solar System

• Terrestrial planets (inner planets)
• Jovian planets (outer planets)
• Small bodies (asteroids, comets, meteoroids)
• Differences in composition and properties between types of planets.

Asteroids

• Asteroids are small, rocky objects that orbit the Sun between the orbits of Mars and Jupiter.
• They are remnants of the early solar system.
• Kirkwood gaps are spaces where asteroids are less numerous.

Comets

• Comets are icy bodies that orbit the Sun.
• Their orbits can be highly elliptical.
• They exhibit a tail when near or close to the Sun, formed by heated material.
• Comets may reside beyond the farthest planets in the Oort cloud or in the Kuiper belt.
• Short-period comets originate in the Kuiper belt; long-period comets originate in the Oort cloud.

Meteors

• Meteors are fragments of interplanetary debris that vaporize as they enter Earth's atmosphere.
• Meteor showers originate from the debris left in Earth's path by passing comets.

Formation of the Solar System

• The solar system formed from a collapsing cloud of gas and dust.
• The central region compressed to form the Sun; the remaining material formed into planets.

Earth's Interiors

• Earth has layers with different densities, compositions (rock type), and pressure.
• Density differences in Earth's layers resulted from the differentiation process
• Gravity, heat from radioactive decay, and early planet impacts drove the early Earth's melting

Earth's Magnetosphere

• A magnetic field protects Earth from harmful particles.
• The magnetosphere extends far beyond Earth's atmosphere.
• Charged particles from the sun are trapped in the van Allen belts.
• Auroras are caused when charged particles interact with gases in Earth's upper atmosphere.

Tides

• The gravitational pull of the Moon and the Sun affect the Earth's oceans, causing tides.
• The Moon's gravity exerts a greater pull on the side of Earth closest to it
• Earth bulges outward in the direction of the Moon, causing a tidal bulge.

Earth's Rotation and Revolution

• Earth rotates on its axis and revolves around the Sun.
• Earth's rotation causes the apparent daily motion of the sky.
• Earth's revolution around the Sun causes the variation of daily sunlight and the appearance of the seasons.

Atmosphere

• Gases that envelope the Earth.
• Chemical composition of the atmosphere affects temperature
• The atmosphere's composition determines the planet's thermal properties.

External Factors

• Density differences, temperature, and internal structure affect a planet's interior
• Volcanic eruptions, Meteoroid impacts and other external factors affect the evolution of a planet's surface.