Ukraine 11 клас Astronomy

1. Introduction

Subject of astronomy

• History of Science: How Our Ideas About Nature Changed – Science grew slowly over 5,000 years. Early civilisations watched the sky to make calendars. Greek thinkers asked why things happen and used reason. Indian and Islamic scholars gave us zero, algebra and careful experiments. In the Scientific Revolution, Copernicus, Galileo and Newton replaced the Earth-centred model with a Sun-centred one and tested ideas by experiment. Modern science brought atoms, evolution, relativity and quantum theory. Each step shows the same lesson: good evidence can overturn old ideas.

2. Celestial sphere and motion of celestial bodies

Celestial sphere and coordinates · Time and calendars · Apparent motions and Kepler’s laws

• Celestial Coordinates: Finding Any Star in the Sky – Astronomers imagine the sky as a huge celestial sphere around the observer. In the horizon system a star is fixed by its altitude (angle above the horizon) and azimuth (angle from north towards east); both change as Earth turns. In the equatorial system a star is fixed by declination (angle from the celestial equator, like latitude) and right ascension (hours east of the March equinox point, like longitude); these stay almost constant, so star maps use them. The altitude of the celestial pole equals the observer's latitude. Brightness is given by magnitude: smaller numbers mean brighter stars.
• Clock and Calendar: Telling Time by the Sky and by Numbers – Our time units come from the sky. One spin of the Earth relative to the Sun is a solar day (24 h); relative to the stars it is a sidereal day (about 23 h 56 min). The Moon's phases repeat every 29.53 days (a month). The Earth goes round the Sun in about 365.2422 days (a year). Calendars are lunar, solar or lunisolar. The Gregorian leap year rule keeps the calendar in step with the seasons. With numbers we can then solve clock problems (angle = |30H − 5.5M|) and calendar problems (odd days).
• Kepler's Laws of Planetary Motion – Kepler gave three rules for how planets move. 1) Each planet moves on an ellipse with the Sun at one focus. 2) The line from the Sun to the planet sweeps equal areas in equal times, so the planet moves faster when it is near the Sun. 3) The square of the time for one round (T²) is proportional to the cube of the semi-major axis (a³). The second law is really conservation of angular momentum. The third law follows from Newton's law of gravitation.

3. Methods and tools of astronomy

Telescopes and detectors

Coming soon

4. Our planetary system

Planets and small bodies

• The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.

5. The Sun

The Sun

• The Sun: Our Star from Core to Corona – The Sun is a star: a huge ball of hot gas (plasma), about 73% hydrogen and 25% helium by mass. It is 1.39 million km wide (109 Earths), holds 99.86% of the Solar System's mass and is about 150 million km away, so its light takes about 8 minutes 20 seconds to reach us. Its surface (photosphere) is about 5500 °C; its core is about 15 million °C. In the core, nuclear fusion joins 4 hydrogen nuclei into 1 helium nucleus; the small mass lost becomes energy (E = mc²). The Sun turns about 4 million tonnes of mass into energy every second. Energy crawls out through the radiative zone (as light, over thousands of years), then rises by convection to the surface. Fusion also makes neutrinos, tiny particles that escape at once and prove fusion is happening. The Sun's magnetic field makes sunspots (cooler, darker patches), flares (sudden blasts) and coronal mass ejections. Activity rises and falls in an 11-year cycle. The solar wind and storms cause auroras and can disturb radio, GPS, satellites and power grids.

6. Stars and stellar evolution

Stars

Coming soon

7. Our Galaxy

Milky Way

• The Milky Way: Our Home Galaxy – The Milky Way is a barred spiral galaxy of about 100–400 billion stars, roughly 100,000 light-years across. It has a thin disc with spiral arms, a central bulge and bar, and a large faint halo with old globular clusters. The Sun sits about 26,000 light-years from the centre in the Orion Arm and orbits at about 230 km/s, once every 230 million years or so. Dust hides much of the disc, so astronomers map the arms using 21 cm radio waves from hydrogen. At the centre is a black hole, Sgr A*, of about 4 million solar masses. The flat rotation curve shows the galaxy holds much more mass than we can see: dark matter.

8. Structure and evolution of the Universe

Galaxies and cosmology

• Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.

9. Life in the Universe

Life beyond Earth

• Astrobiology: Is There Life Beyond Earth? – Astrobiology is the science that asks whether life exists beyond Earth. Life as we know it needs liquid water, energy and carbon chemistry. The habitable (Goldilocks) zone is the range of distances from a star where a planet could keep liquid water. Scientists search Mars, icy moons such as Europa and Enceladus, and thousands of exoplanets, look for biosignatures in their air, and listen for signals (SETI). The Drake equation estimates how many talking civilisations might exist; the Fermi paradox asks why we have not heard from any.