8th Grade The Universe

The Universe Components of the Universe: ❖ Galaxy: a large group of stars, gas, and dust held together by gravity ➢ Spiral Galaxy: a galaxy with a bulge in the center and distinctive arms that radiate outward ■ the Milky Way, the galaxy we live in, is a type of spiral galaxy ➢ Elliptical Galaxy: an oval-shaped galaxy composed of older, low-mass stars ➢ Irregular Galaxy: a galaxy that does not have a distinct regular shape ❖ Nebula: a cloud of gas and dust in which new stars are formed ❖ Star: a large sphere of extremely hot and glowing gas Stars: A star is a ball of plasma held together by its gravity. There are tens of billions of stars in our universe. Nuclear reactions occur in stars and energy from the reactions is released as electromagnetic radiation. The Sun is a medium-sized star located in a spiral arm of the Milky Way. The Sun is many thousands of times closer to Earth than any other star. Characteristics: ❖ Magnitude ➢ A measure of luminosity or brightness ➢ Apparent Magnitude: How bright a star appears to be ➢ Absolute Magnitude: How bright a star actually is ❖ Temperature and Color ➢ The color of a star indicates the temperature of the star ➢ Stars can be classified by temperature ■ Decreasing temperatures means the star is becoming dimmer. Brighter stars generally mean hotter stars. ■ Classes of stars: O, B, A, F, G, K, M Life Cycle: A star’s life cycle is determined by its mass. Stars begin their lives as clouds of dust and gas called nebulae. Gravity causes the nebula to contract. If the star is of an average mass, it will become a red giant then a planetary nebula before becoming a white dwarf. If the star is of a larger mass, it will become a red supergiant before a supernova, where it can then become either a neutron star or a black hole. White Dwarf: a star of high density and temperature and low luminosity Giant: a star with a large radius and high luminosity Supergiant: a star of a massive radius and the highest luminosity Electromagnetic Spectrum: Wave: a disturbance in space that transfers energy A wave is of high frequency if it has a short wavelength and high energy. A wave is of low frequency if it has a high wavelength and low energy. The electromagnetic spectrum is a range of electromagnetic waves that transfer energy through electromagnetic radiation. The spectrum consists of seven types of waves. ● Radio Waves: Radio waves are used for communication such as television, mobile phones, and radios. They have the longest wavelength on the spectrum. ● Microwaves: Microwaves can be used when transmitting the information. These waves can penetrate rain, snow, clouds, and smoke which make them ideal for transmitting. ● Infrared Waves: Infrared waves can be used to reveal an area or object that can not be seen. These waves produce heat and this heat can be picked up to identify objects. These waves can pass through dense regions of dust and gas. Image: https://commons.wikimedia.org/wiki/File:EM_Spectrum_Properties_reflected.svg ● Visible Light Waves: Visible light waves are the waves we can see and they appear as colors. The colors each have a different wavelength. When these waves are out together, we get light. ● Ultraviolet (UV) Waves: UV waves are non-visible waves emitted by the Sun. They provide our bodies with warmth and vitamin D, but if we are overexposed to these waves, our skin tans and/or burns. ● X-ray Waves: X-ray waves have very small wavelengths. They are used by doctors and dentists to scan images of your teeth and bones. ● Gamma Waves: Gamma waves are produced only by the hottest regions in the universe. These include supernova explosions, destruction of atoms, and decaying radioactive material in space. Bursts of these waves can release more energy in ten seconds than the Sun can in its entire lifetime of ten billion years. Our Expanding Universe: The Doppler Effect: The waves a moving object emits can become either stretched or compressed. If the object is moving towards you, the waves will compress and have a shorter wavelength and higher frequency. If the object is moving away from you, the waves will stretch out and have a longer wavelength and lower frequency. This same idea applies to light waves. Red light has longer wavelengths and blue light has shorter wavelengths. Redshift is when an object is moving away from you, meaning its waves are stretched out and have a longer wavelength. It is called redshift because when an object is moving away, the spectral lines seen on the electromagnetic spectrum are shifted towards the red end. Blueshift is when an object is moving towards you, meaning its waves are compressed and have a shorter wavelength. It is called blue shift because when an object is moving towards you, the spectral lines seen on the electromagnetic spectrum are shifted towards the blue end. If a star is moving towards you while emitting light, the light goes bluer. If it is emitting light while moving away from you, the light goes red. If the star is not moving at all but still emitting light, the color of the light looks the same in every direction. Expansion of the Universe: All galaxies in our universe show a redshift of their spectral lines, meaning that these galaxies are all moving away from us and each other. The bigger the redshift, the faster the object is moving and the further away it is, indicating that the universe must be expanding.