Copy of Physics- Space Unit Test

Physics Space Unit- Study Guide

1. For Our Eyes Only

a) Frames of Reference- Everything appears to move from our frame of reference. This is a set of axes of any kind that is used to describe the positions or motions of things. For example, the equator and prime meridian are the axes that we use to describe horizontal and vertical locations on Earth.

b) Ancient peoples-They watched the motions of celestial bodies (the Sun, Moon, stars, and planets). Ancient civilizations, such as the ancient Greeks, Babylonians, Hindus, and Egyptians, built up a body of knowledge from their observations:

c) Constellations- The stars make unchanging patterns in the sky called constellations. These patterns look like objects.

d) Polaris/North Star- The stars appear to revolve around one point in the sky, which is very near Polaris, or the North Star. Polaris never rises or sets, so early people used it to find direction at night. The southern hemisphere doesn’t have a South Star, but instead has the constellation Crux (the Southern Cross), whose long axis

points toward the South Celestial Pole.

2. Sky Coordinates

a) The azimuth- is (also known as a bearing) is an angle measured clockwise

from the north.

b) The Altitude- Next, measure the altitude by measuring the celestial body’s angle

above the horizon in degrees.

c) The altitude-azimuth coordinates- These two angles are called altitude-azimuth coordinates. They locate a celestial body relative to a fixed Earth. These two coordinates for each celestial body change depending on the time of the reading, e.g. the Moon’s location changes throughout the day.

d) Astrolabe- An astrolabe is a device used to measure the altitude of an object. It was invented by the Greeks. The pointer on it is aimed toward a star. The angle (altitude) is measured from the horizontal.

e) Compass- A compass is used to measure an object’s azimuth. With these

tools, navigation was improved and the great sea explorations of the world began.

3.The Stars as a Frame of Reference

a) Mars and the stars- It is simple to use the stars as a frame of reference. Suppose you want to see the actual movements of the planet Mars. Find Mars in the night sky. Next, find a few very bright stars near Mars. Mark down Mars’s position relative to those few bright stars. The next night you would find Mars and the few bright stars in the sky again. Mark it down. If you made similar observations over several weeks, you could see in which direction Mars is really moving.

b) The Geocentric model- The geocentric model is a debunked theory that the Earth is the center of the universe, with the sun and planets revolving around it. The geocentric model was accepted for nearly 1,500 years.

c) The Heliocentric Model- In the early 1500’s, Polish astronomer Nicholas

Copernicus proposed a Sun-centered or heliocentric model to explain the view from Earth. He placed the Sun in the center, with a rotating Earth revolving around it.

d) Solstice- marks the longest period of daylight or shortest period of daylight in the year.

e) Equinox - represents days of equal length. Dates are shown on the diagram.

f) Universal Gravitation- This law provided an explanation for the planets’ elliptical orbits. There is a gravitational force, or pull, between all objects. If there is no force acting on an object, it will move in a straight line at a constant speed.

3. The Spectroscope: New Meanings in Light

a) A spectroscope- If you pass a beam of light through a narrow slit before sending it through a prism, the resulting spectrum shows much finer detail. A spectroscope is

a device that produces this kind of focused spectrum.

b) Spectroscopy: The Science of Colour- Each element has a unique and particular set of spectral lines. Each spectrum can be used to identify an element. For example, if a sample is tested and has the lines below, you can conclude that the sample contains hydrogen.

c) Diffraction Gratings- Like waves in a pool, the Sun’s light energy ripples out through space. Some spectroscopes use prisms to split the light into a spectrum, but a diffraction grating can also split the light. It is made of thousands of closely spaced slits. Modern spectroscopes use diffraction gratings instead of prisms to split the light into spectra.

d) Absorption -If white light is passed through a cooler substance, the spectrum observed is a continuous spectrum with dark gaps between colors. This is called an absorption or dark line spectrum.

e) Spectral analysis- Astronomers use this spectral analysis method to learn about distant stars, but the stars are much dimmer than the Sun, and astronomers can’t identify the hundreds of lines in their spectra.

f) Doppler Effect- You have probably noticed that the siren on an ambulance or fire truck sounds different as the vehicle approaches, passes, and then moves away from you. The change in the siren’s pitch is called the Doppler effect. The Doppler effect can be used to measure the speed and direction of light-emitting objects such as stars.

4. Bigger and smarter Telescopes

a) Optical telescopes give us information based on visible light. However, objects in space, such as stars and galaxies, also emit electromagnetic energy in the form of radio waves, infrared (heat) waves, and X-rays.

b) Wavelengths and Frequency

As wavelengths go up the frequency goes down.

As wavelengths go down the frequency goes up.

c) Radio telescopes have several advantages over optical telescopes:

• They are not affected by weather.

• Signals can be detected during the day and at night.

• They are not distorted by clouds, pollution, or the atmosphere as are light waves.

• They can detect information from regions of the universe that appear empty.

d) Radio telescopes- Radio telescopes are a metal-mesh curved dish with a receiver in the middle. The curved portion intercepts and focusses radio waves before transmitting them to the receiver as an electrical signal. The wavelength of light is one factor for the resolving power of telescopes – the smaller the wavelength, the

better the resolving power.

e) Radio interferometry- As with optical telescopes, several small radio

telescopes can be arranged into groups (called arrays) to achieve greater resolving power than one large radio telescope can achieve.

f) Radio astronomers can connect their telescopes without wires, called very long baseline interferometry. Now radio telescopes from anywhere around the world can be connected and signals can be combined.

5. Distance to the Stars

Triangulation: This is a technique in measuring the distance to a star. To do this, you need to:

1. Create a baseline. The distant object will be viewed from each end of the baseline. Mark off a long, straight line.
2. Measure the angles to the object at each end of the baseline.
3. Make a scale drawing of the triangle that is formed. Draw the baseline and the angles that are formed at each end. Extend the sides of the triangle until they cross at the location of the object.
4. Measure the shortest distance(the perpendicular line) to the baseline. This is the distance of the object.

Parallax is used to determine distances to nearby stars. To create the longest baseline possible without leaving Earth, angles are measured when the Earth is farthest from the Sun (with Earth’s elliptical orbit, measurements are taken in January and June). The stars behind the one being measured appear to have changed in position, which is called parallax. This helps to measure the parallax angle.

Light-year: Since the universe is so large, the distance must be measured in different units such as light years.

Important terms

-One AU is the distance from Earth to the Sun

-1 AU = 1.5 x 108 km or 150 million km