Definition
The Sun generates its energy through nuclear fusion: hydrogen nuclei fuse together under immense gravitational pressure and temperature at its core to form helium, releasing enormous energy in the process (via , since the resulting helium has slightly less mass than the hydrogen that formed it). Hydrogen and helium are the Sun's two main constituent elements.
A planet's surface temperature is primarily determined by its distance from the Sun (closer means more solar energy received per unit area) and its atmospheric composition — particularly the presence of greenhouse gases, which trap outgoing heat and raise surface temperature beyond what distance alone would predict.
Planets are compared using factors such as size, mass, density, distance from the Sun, atmospheric composition, surface temperature, and number of moons.
Remember
Gas giants like Jupiter have lower density than rocky planets like Earth or Mars despite being much larger, because they're made mostly of light gases (hydrogen and helium) with no solid rocky surface, while rocky planets are made of denser materials like iron, silicon, and rock packed tightly together — size alone doesn't determine density; composition and internal structure do.
Two planets receiving identical sunlight can still end up at very different surface temperatures if their atmospheres differ: a planet with a thick atmosphere rich in greenhouse gases traps much more outgoing heat than one with a thin atmosphere or little greenhouse gas, so atmospheric composition can matter as much as distance from the Sun.
Definition
Cyclones form primarily over warm ocean waters because warm water evaporates rapidly, and the resulting warm, moist air rises quickly, creating a strong low-pressure zone that draws in surrounding air — this rising, spiralling air, continuously fed by more evaporation from the warm ocean surface, is what powers and sustains the storm.
The Coriolis effect (caused by Earth's rotation) deflects the air flowing into this low-pressure zone, curving it into the spiral rotation characteristic of a cyclone rather than flowing straight inward — without Earth's rotation, air would simply flow directly into the low-pressure centre without organizing into a rotating storm system at all.
Cyclones weaken rapidly once they move over land, because they lose their fuel source: the warm, moist ocean air that continuously feeds their rising convection currents is cut off, and increased surface friction over land also disrupts their organized circulation.
Remember
Global warming intensifies hurricanes/cyclones because warmer ocean surface temperatures mean more evaporation and more energy available to feed the storm's convection, allowing cyclones to grow stronger and hold more moisture (leading to heavier rainfall) than they would over cooler waters.
Definition
Carbon dioxide contributes the most to global warming among greenhouse gases overall, due to the sheer volume released by human activity (burning fossil fuels), even though other gases like methane trap more heat per molecule.
Rising sea levels are primarily caused by two effects of global warming: thermal expansion of ocean water as it warms (water takes up more volume when hotter), and melting of land-based ice (glaciers and ice sheets), which adds new water into the oceans that wasn't there before.
Definition
Background radiation is the low level of ionizing radiation always present in the environment, from both natural and human sources. Natural sources include cosmic rays from space, radioactive elements in rocks and soil (terrestrial sources), and radon gas seeping from the ground — these together form a fairly constant baseline that human activity fluctuations don't significantly change, since natural sources vastly outweigh typical human contributions in most locations.
A significant human-linked source of background radiation is medical procedures (such as X-rays and radiotherapy), though this remains small compared to natural background levels for most people.
Definition
Three safety measures for handling radioactive materials: (1) shielding — using lead, concrete, or thick material to absorb radiation before it reaches people; (2) distance — keeping as far as practical from a radioactive source, since radiation intensity falls off rapidly with distance; (3) limiting exposure time — spending the minimum time necessary near a source, since total dose received depends on how long you're exposed.
Quick Recap
- ●Sun's energy: hydrogen fusing into helium (nuclear fusion), via
- ●Surface temperature: distance from Sun atmospheric/greenhouse gas composition
- ●Gas giants: low density (light gases, no solid surface). Rocky planets: high density (packed solid material)
- ●Cyclones: warm ocean water fuels rising moist air; Coriolis effect creates the spiral; weaken over land (fuel cut off)
- ●CO dominates warming by sheer volume; sea level rise: thermal expansion melting land ice
- ●Background radiation: cosmic terrestrial sources, fairly constant; safety shielding, distance, limited time
