| A | B |
|---|
| Solar System | The Sun and its family of orbiting planets, moons, and other objects. |
| Galaxy | Millions or billions of stars held together in a group by their own gravity. |
| Universe | Space and all the matter and energy in it. |
| Constellation | A group of stars that form a pattern in the sky. |
| Orbit | The path of an object in space as it moves around another object due to gravity; for example, the Moon moves in an orbit around Earth. |
| Orbit | To revolve around, or move in an orbit; for example, the Moon orbits Earth. |
| Electromagnetic radiation | Energy that travels across distances as certain types of waves |
| Wavelength | The distance from one wave crest to the next crest; the distance from any part of one wave to the identical part of the next wave. |
| Spectrum | Radiation from a source separated into a range of wavelengths. |
| Spectrum | The range of colors that appears in a beam of visible light when it passes through a prism. See also electromagnetic radiation. |
| Telescope | A device that gather visible light or another form of electromagnetic radiation. |
| Satellite | A body that orbits a more massive body. A natural satellite is also called a moon. |
| Space station | A satellite in which people can live and work for long periods. |
| Lander | A craft designed to land on a planet’s surface. |
| Probe | A spacecraft that is sent into a planet’s atmosphere or onto a solid surface. |
| axis of rotation | an imaginary line about which Earth turns |
| revolution | the motion of one object around another |
| season | patterns of temperature changes and weather trends over the course of a year |
| equinox | occurs when sunlight shines equally on the northern and southern hemispheres |
| solstice | occurs when the amount of sunlight is greatest in one hemisphere |
| mare | a dark area on the Moon |
| eclipse | occurs when a shadow makes the Sun or the Moon seem to grow dark |
| umbra | the darkest part of the shadow |
| penumbra | a spreading cone of lighter shadow around the umbra |
| asteroids | Small, solid, rocky bodies that orbit close to the Sun. |
| gas giants | The four largest planets—Jupiter, Saturn, Uranus, and Neptune—that are made mainly |
| tectonics | The processes of change in a crust as a result of the motion of hot material underneath. |
| meteor | When a particle enters Earth’s upper atmosphere and the particle and the air around it |
| meteorite | A space object that passes through Earth’s atmosphere and reaches Earth’s surface. |
| astronomical unit | Earth’s average distance from the Sun. |
| comet | A small, icy object that produces a coma when it gets close to the Sun. |
| volcanism | A process that moves molten rock from a planet’s interior onto its surface. |
| ellipse | The shape of the planets’ orbits in our solar system. |
| terrestrial planets | Small, solid, rocky bodies that orbit close to the Sun. |
| ring | A wide, flat zone of small particles around a planet’s equator. |
| tectonics | This process shaped mountains, valleys, and other features on Earth and other space bodies. |
| astronomical unit | This is equal to about 150,000,000 kilometers. |
| ellipse | flattened circle or oval |
| volcanism | This is the eruption of molten material onto a planet’s surface. |
| gas giants | The four largest planets in the solar system |
| meteor | These are found far from the Sun, so they are made of rock and some metal. |
| comets | These are found far from the Sun, so they are made of different ices as well as rock and some metal. |
| terrestrial planets | The closest planets to the Sun—Mercury, Venus, Earth, and Mars—that all have rocky |
| asteroids | Most of these have paths that keep them between the orbits of Mars and Jupiter. |
| convection | the transfer of energy from place to place by the motion of heated gas or liquid |
| fusion | a process in which particles of an element collide and combine to form a heavier element, such as the fusion of hydrogen that occurs in the Sun’s core |
| big bang | the moment in time when the universe started to expand out of an extremely hot, dense state, according to scientific theory |
| main sequence | the stage in which stars produce energy through the fusion of hydrogen into helium |
| black hole | the final stage of an extremely massive star, which is invisible because its gravity prevents any form of radiation form escaping |
| quasar | the very bright center of a distant galaxy |
| Doppler effect | a change in observed frequency of a wave, occurring when the source of the wave or the observer is moving |
| nebula | a cloud of gas and dust in space from which stars form |
| parallax | the apparent shift in the position of an object when viewed from different locations |
| light-year | the distance light travels in one year, which is about 9.5 trillion kilometers (6 trillion miles) |
| solar wind | a stream of electrically charged particles that flows out in all directions from the Sun’s corona |
| sunspot | a darker spot on the photosphere of the Sun |
| corona | the outer layer of the Sun’s atmosphere |
| Neutron star | A dense core that may be left behind after a higher-mass |
| Day and Night | What are the results of Earth's rotation on its axis? |
| Earth's orbit and the 23-degree tilt of its axis | What causes seasons? |
| on or around June 21 | When is the Sun highest in the sky near the North Pole? |
| Impact craters | round features caused by collisions with space objects |
| The Moon causes tides on Earth by producing | two bulges of water, one toward and one away from the Moon |
| changing hydrogen into helium through fusion | The Sun produces energy by |
| Core | Which layer of the Sun's interior is the densest? |
| prominence | Which feature of the Sun appears as a loop in the Sun's atmosphere? |
| new and then waxing crescent | During the first week of the phases of the Moon, the Moon is |
| White dwarf or black dwarf | What are is part of the life cycle of a lower-mass star? |
| Distance from Earth | Astronomers measure parallax to determine a star's |
| 12 hours of daylight and 12 hours of darkness | Each day at the equator there are about |
| Spiral | The Milky Way is what kind of galaxy? |
| Old stars | Elliptical galaxies are made of mostly |
| Quasar | very bright center of a galaxy |
| Big bang | Microwave radiation is evidence of what space event? |
| Seasons | Patterns of temperature changes and weather trends over the course of a year |
| Black hole | The final stage of an extremely massive star, which is invisible because its gravity prevents any form of radiation from escaping. |
| Main Sequence | The stage in which stars produce energy through the fusion of hydrogen into helium. |
| quasar | The very bright center of a distant galaxy. |
| Nebula | A cloud of gas and dust in space. |
| Doppler effect | A change in the observed frequency of a wave, occurring when the source of the wave or the observer is moving. |
