Observing the Local Sky and Circling the Sky

Observing the Local Sky

• Stars, planets, and the moon are visible to the naked eye at night.
• Cultures have named patterns of stars as constellations.
• Early astronomers used constellations for navigation and calendars.
• Today's astronomers use constellations to define large areas of the sky.
• Stars appear to move across the sky due to Earth's rotation.
• The celestial sphere is a model where the stars appear to be fixed on a sphere.
• Stars in a constellation may appear close together but are often vastly different distances from Earth.
• The celestial sphere is a model to visualize star positions.

Circling the Sky

• Stars appear to rise in the east and set in the west due to Earth's rotation.
• To locate any object in the local sky, two angles are needed.
• Azimuth and altitude are used to locate any object precisely.
• The local sky is the sky as seen from a particular location on Earth.
• Zenith is the point directly overhead.
• The meridian is the imaginary half-circle from North through Zenith to South.

Celestial Coordinate System

• The local sky can be extended to the whole Earth, creating a geographical coordinate system: longitude and latitude.
• Longitude lines measure East-West positions from a prime meridian.
• Latitude lines measure North-South positions from the equator.

The Moon

• The Moon is the Earth's closest and second brightest celestial body.
• Phases of the Moon involve changes in the Moon's appearance as seen from Earth.
• The Moon orbits Earth, causing its appearance to change based on its position relative to the Sun.
• A full moon occurs when the Earth-Moon-Sun line is nearly straight with the Sun behind Earth.
• Eclipses occur when the Earth or the Moon cast a shadow on the other body, which may result in a Lunar or Solar Eclipse.

The Seasons

• The seasons are caused by the tilt of Earth's axis relative to its orbital plane.
• Solstices and Equinoxes are specific points in Earth's orbit around the sun.
• Solstices represent the longest and shortest days of the year.
• Equinoxes represent equal days and nights.
• The period of time from one equinox to the next is called a tropical year.

Precession of Earth's Axis

• Earth's axis slowly rotates (precesses) in a cycle of roughly 26,000 years.
• This precession is caused by gravitational forces exerted by the Sun, Moon, and other planets upon Earth.
• The changing orientation of Earth's axis affects the seasons over very long periods.

Observing Techniques

• Telescopes collect light from celestial objects.
• Refracting telescopes use lenses to focus light, while reflecting telescopes use mirrors.
• The size of the mirror or lens is a key factor determining light collection and clarity.
• Spectrometers determine the properties of light coming from distant objects.
• Spectrometers display wavelengths, which provide information about the composition/temperature of objects.

Electromagnetic Radiation

• Electromagnetic waves are one form of energy transfer.
• Visible light is only a small part of the electromagnetic spectrum, which includes radio waves, infrared, ultraviolet, x-rays, and gamma rays.
• The intensity of wavelengths provides information about objects in space.
• Spectroscopy is used to learn more about the composition and temperature of distant objects.

Law of Radiation

• Wien's law relates a particular object's temperature to the wavelength at which it emits the most radiation.
• The Doppler effect describes the apparent change in wavelength of radiation observed by an observer in relation to the motion of a source or object.

Astronomical Instruments

• Various tools, such as telescopes, are used to make observations of sky objects.
• Telescopes collect light and magnify images.
• Light collection is dependent on the size of the lens/mirror, with larger instruments capable of collecting more light and providing better views.

Understanding the Solar System

• The Solar System includes our Sun and the planets orbiting it.
• Planets are categorized as either terrestrial or Jovian planets, possessing different characteristics.
• Planets in the solar system orbit the sun, with elliptical rather than circular orbits.
• Planets and moons have moons, or other satellites orbiting them.
• Asteroids, comets, and other space debris orbit the sun in various locations, particularly outside the orbit of the classical planets.
• Studying the differences in planetary characteristics can help us understand their formation.

The Interiors of the Solar System

• Earth has several layers, with the crust (on the outside), the mantle, then outer and inner cores.
• The interior temperature and pressure create these layers.
• Radioactivity and large impact events can contribute to the interior's temperature.
• Other planets have similar internal structures, although compositions may differ.

Earth's Magnetosphere

• Earth has a magnetosphere, which is a region of space where Earth's magnetic field is dominant.
• The shape and size of Earth's magnetosphere are influenced by solar winds.
• Charged particles, originating from the Sun's solar wind, are trapped in the Van Allen radiation belts.
• These trapped particles occasionally escape and generate beautiful displays of light called the Aurora Borealis and Aurora Australis.

The Tides

• The gravitational forces between Earth, the Moon, and the Sun cause tides.
• The Moon and Sun exert gravitational forces, causing slight bulges in oceans on the side of Earth that faces and opposite side.

Other Planets

• Different planets have their own characteristics.
• Various surface features, atmospheric composition, and magnetic fields differ between planets.
• Understanding planetary differences, such as the composition of the atmosphere, is a way to understand a planet's possible formation.

Light, Radiation, and the Spectra

• Studying different types of electromagnetic radiation (light) and their spectra can give information about objects' composition, temperature, and motion.
• Each element has a unique "fingerprint" or spectrum that can be used to identify its presence in objects.
• Understanding wavelength spectra provides clues on the properties of objects in Space and how they form.