Astronomy: Moon, Planets, and Sun

Motion of the Moon

• The Moon is constantly falling towards Earth due to gravitational attraction.
• The Earth and Moon orbit around a common center of mass which is closer to the Earth because Earth is more massive.

Classifying Planets

• Traditionally, planets were classified into two groups: inner rocky planets and outer gas giants.
• Pluto's characteristics did not align with either group.
• With discovery of smaller, icy bodies, the solar system was divided into:
  • Inner terrestrial planets
  • Outer gas giant planets
  • Dwarf planets and comets

Properties of the Sun

• The Sun is the largest object in the solar system in terms of diameter and mass.
• It's so large it would take 109 Earths or 10 Jupiters lined up to cross its diameter.
• The Sun is made up of mostly gas due to its high temperature.
• The Sun's center is composed of atomic nuclei and electrons.
• It produces a massive amount of energy equal to trillions of lightbulbs shining every second.

The Sun's Atmosphere

• The solar atmosphere is divided into three layers:
  • Photosphere: The visible surface of the Sun, innermost layer of the atmosphere.
  • Chromosphere: Located outside the photosphere, visible during solar eclipses. Emits UV radiation.
  • Corona: Outermost layer of the atmosphere, visible during eclipses. Extremely hot and emits X-rays.

Solar Activity

• The Sun exhibits changes in its features called solar activity.

• Magnetic fields in the solar atmosphere cause disturbances and create new features.

• Types of features on the Sun:

  • Sunspots: Darker, cooler regions where intense magnetic fields penetrate the photosphere. Often occur in pairs with opposite magnetic polarity.
  • Coronal Holes: Areas of low density and low temperature in the corona. Responsible for escaping solar wind particles.
  • Solar Wind: A stream of plasma flowing out from the corona. Bathes the planets in a flood of particles and is responsible for auroras.
  • Solar Flares: Violent eruptions of particles and radiation from the Sun's surface. Associated with sunspots.
  • Prominence: Arcs of gas ejected from the chromosphere or gas condensing in the corona that rains back to the surface.

• The number of sunspots varies in a predictable 11-year cycle, linked to reversals in the Sun's magnetic field.

Solar Interior

• The Sun's energy originates from nuclear fusion in its core.
• Fusion combines lightweight nuclei into heavier nuclei.
• The Sun's core fuses hydrogen into helium, releasing energy in the process.
• The Sun is estimated to have about 5 billion years left.
• It has only used around 3% of its hydrogen fuel.

Energy Transport in the Sun

• There are two zones responsible for transferring energy from the core to the surface:
  • Radiation zone: Inner portion of the Sun extending to 86% of its radius where energy travels by radiation.
  • Convection zone: Extends from the radiation zone to the photosphere where energy travels by convection.
• The Sun emits energy in various wavelengths, a small fraction of which reaches Earth.

Spectra

• Spectra are the arrangement of visible light based on wavelengths, often observed after passing light through a prism.

• Three types of spectra exist:

  • Continuous spectrum: Contains all wavelengths without breaks. Produced by glowing solids, liquids, or highly compressed gas.
  • Emission spectrum: Contains bright lines at specific wavelengths. Produced by non-compressed gas. Wavelengths are specific to the element emitting the light.
  • Absorption spectrum: Contains dark lines at specific wavelengths. Produced when cooler gas absorbs light from a source that emits a continuous spectrum.

• Comparing laboratory spectra helps scientists identify the elements in the Sun's outer layer.

The Sun's Composition

• Analysis of the Sun's absorption spectrum reveals its composition:

  • 71% hydrogen
  • 27.1% helium
  • Small amounts of other elements

• The composition is similar to gas giant planets, suggesting a common origin in an interstellar cloud.

• The heavier elements in terrestrial planets likely originated from long-extinct stars.

• The Sun's composition represents the composition of the galaxy as a whole.

Patterns of Stars

• Ancient civilizations grouped stars into constellations, named after animals, mythological characters, or everyday objects.
• Today, astronomers recognize 88 constellations.
• Types of constellations:
  • Circumpolar constellations: Visible all year round in specific hemispheres, such as Ursa Major.
  • Seasonal constellations: Visible during specific seasons due to Earth’s orbit, such as Orion and Hercules.
  • Zodiac constellations: Located along the ecliptic plane, seen in both hemispheres.

Star Clusters

• Stars can be grouped together in star clusters:
  • Open clusters: Relatively loose groups of stars, several hundred to a few thousand.
  • Globular clusters: Tightly packed spheres of thousands or millions of stars. Usually older than open clusters.

Life Cycle of Stars

• The life cycle of a star is determined by its mass:
  • Main-sequence phase: Fusion of hydrogen to helium in the star's core. Size and lifespan vary based on mass.
  • Red Giant phase: Hydrogen is depleted in the core, and fusion continues in a shell. The star expands, cools, and becomes more luminous.
  • Final stages: The star's evolution depends on its mass:
    • Low-mass stars: The core becomes a white dwarf, surrounded by a planetary nebula, eventually cooling to become a black dwarf.
    • Massive stars: Explode as supernovae, creating heavier elements and leaving behind remnants like neutron stars or black holes.

Life Cycle Of Massive Stars

• Massive stars follow a similar life cycle to smaller stars, but their phases are more extreme.
• They go through multiple stages of fusion creating heavier elements, expanding into a supergiant phase.
• When iron is formed in the core, the lack of further fusion leads to a core collapse and a supernova explosion.
• Supernovae create elements heavier than iron and leave behind neutron stars or black holes.

Explore the fascinating concepts of the motion of the Moon, the classification of planets, and the properties of the Sun. This quiz covers gravitational effects, planetary groups, and the Sun's composition and energy output. Test your knowledge and understand our solar system better!