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Tap a card to reveal its definition. Only one card stays open at a time, and each card closes after 8 seconds. You may reopen any card as often as you need. When you are ready, complete the matching activity underneath.
Click a term on the left, then click the description on the right that matches it.
Every object in the universe hotter than absolute zero is broadcasting. Stars, planets, dust clouds, and even the cold vacuum between galaxies release electromagnetic radiation — energy carried by linked oscillating electric and magnetic fields that need no medium at all. In a vacuum, every one of these waves travels at exactly the same speed, roughly 3.00 × 108 meters per second. Because the speed is fixed, wavelength and frequency are locked together in an inverse relationship: stretch the wave out and fewer cycles pass you each second; squeeze it down and more do.
That single relationship organizes the entire spectrum. It also explains a second, less obvious pattern. Light does not deliver its energy continuously; it arrives in discrete packets called photons, and the energy of each photon is directly proportional to its frequency. Radiation with a short wavelength therefore has a high frequency and a high energy per photon. A single ultraviolet photon can break a chemical bond in your skin. A microwave photon, carrying roughly a millionth as much energy, cannot.
Page 14 of the Earth Science Reference Tables displays the portion of the spectrum most useful in Earth and Space Sciences. Read it carefully, because its layout is deliberately reversed from what many students expect. Wavelength, printed in nanometers along the upper axis, increases toward the right. Frequency, printed in hertz along the lower axis, increases toward the left. The bold arrow at the bottom of the chart states the consequence directly: energy increases in the same direction as frequency. The visible band — violet at roughly 4.0 × 102 nm through red at 7.0 × 102 nm — occupies a startlingly thin sliver of the chart, which is exactly the point. Human eyes sample less than one percent of the information arriving from the sky.
Astronomers therefore treat wavelength as a filter for choosing which physical process they want to study. Cold dust and forming planets glow in the infrared. Hot young stars pour out ultraviolet. Gas heated to millions of kelvins near a black hole emits X-rays. The faint afterglow of the early universe has cooled all the way down into the microwave band. Distance adds a further complication: as the universe expands, radiation from remote galaxies is stretched toward longer wavelengths, an effect called redshift. Visible light emitted by the first galaxies has been stretched so far that it now reaches us as infrared. To look at the oldest objects in the universe, you must build an instrument that sees a band your eyes cannot.
1 Complete each sentence using a word from the bank. Tap a blank, then tap a word.
2 Arrange the words to form a correct sentence. Tap words in order; correct placements turn green.
3 Expand the bare-bones sentence below into one detailed sentence. Use the prompts.
4 A star emits its peak radiation at a wavelength of 5.3 × 102 nm. According to ESRT page 14, this radiation is
5 Which list places these forms of electromagnetic radiation in order of increasing wavelength?
6 Which row in the table below correctly compares ultraviolet radiation to microwave radiation?
| Row | Wavelength | Frequency | Energy per Photon |
|---|---|---|---|
| (1) | Longer | Higher | Greater |
| (2) | Shorter | Lower | Less |
| (3) | Shorter | Higher | Greater |
| (4) | Longer | Lower | Less |
7 Visible light emitted by the earliest galaxies now arrives at Earth with a wavelength near 2.0 × 103 nm. Which statement best explains this observation?
A telescope performs only two jobs, and neither one is magnification. Its first job is to collect light — to intercept a larger area of the incoming wavefront than a human pupil can. Its second job is to resolve that light, separating two sources that lie close together on the sky. Both jobs are governed by a single number: the diameter of the main optical element, called the aperture. Because collecting area scales with the square of the diameter, doubling the aperture quadruples the light gathered. A 2.4-meter mirror collects sixteen times the light of a 0.6-meter mirror, which is the difference between recording a galaxy and recording nothing at all.
Early telescopes were refractors, using a lens to bend light to a focus. Refractors suffer a fundamental flaw: glass bends short wavelengths more sharply than long ones, so violet and red light focus at different distances and every bright star is fringed with false color. This is chromatic aberration. Large lenses also sag under their own weight, because a lens can only be supported at its rim. Nearly every research instrument built in the last century is therefore a reflector, using a curved mirror. A mirror reflects all wavelengths at the same angle, eliminating chromatic aberration entirely, and it can be braced across its entire back surface. The largest telescopes now use dozens of hexagonal mirror segments aligned to a fraction of a wavelength.
Aperture, however, cannot solve the atmosphere. Air is not uniformly transparent. Ozone and molecular oxygen absorb essentially all incoming ultraviolet, and the atmosphere is completely opaque to X-rays and gamma rays. Water vapor and carbon dioxide absorb most of the infrared. What remains are two narrow atmospheric windows: a visible window near 4 × 102 to 7 × 102 nm, and a much wider radio window at wavelengths longer than about 1 × 107 nm. Everything else must be observed from above the atmosphere. This is why the Hubble Space Telescope works in ultraviolet, visible, and near-infrared from low Earth orbit, and why the James Webb Space Telescope was placed roughly 1.5 million kilometers from Earth, shaded by a tennis-court-sized sunshield and chilled below 50 K — a warm infrared telescope would drown in its own glow.
Human activity has narrowed even the windows that remain. Outdoor lighting scattered by the atmosphere produces skyglow, which raises the background brightness and erases the faintest visible objects; roughly four-fifths of North Americans can no longer see the Milky Way from home. Radio observatories face the parallel problem of radio-frequency interference from mobile networks and satellite constellations. Communities near major observatories have responded with shielded-lighting ordinances and legally protected radio quiet zones — design solutions that restore access to a natural resource without prohibiting its use.
The graph below shows the percentage of incoming radiation blocked by Earth's atmosphere at each wavelength. Low points on the curve are atmospheric windows.
Use the graph above to complete every cell.
| Radiation | Wavelength (nm) | Percent Blocked by Atmosphere | Best Observatory Location |
|---|---|---|---|
| Gamma ray | 1 × 10−3 | ||
| Visible (yellow-green) | 5.5 × 102 | ||
| Mid-infrared | 1 × 104 | ||
| Radio | 1 × 108 |
8 Complete each sentence using a word from the bank.
9 Arrange the words to form a correct sentence.
10 Expand the bare-bones sentence below into one detailed sentence. Use the prompts.
11 Based on the graph above, radiation with a wavelength of 1 × 104 nm cannot be studied effectively from Earth's surface because
12 Telescope A has an aperture of 2.4 m and Telescope B has an aperture of 0.6 m. Compared to Telescope B, Telescope A gathers
13 The James Webb Space Telescope is kept below 50 K and shielded from the Sun. This design requirement exists because
14 A town near a research observatory passes an ordinance requiring all outdoor lights to be shielded and pointed downward. This design solution primarily
A research team wants to image a cold dust cloud in which new stars are forming. Visible light from inside the cloud is almost completely blocked by dust grains, but infrared radiation passes through the same dust with little loss. The team must choose between two instruments already in operation. Some information about the two telescopes is shown in the table below.
| Telescope | Aperture (m) | Primary Band Observed | Location | Servicing |
|---|---|---|---|---|
| Mauna Loa Optical | 3.6 | Visible | Mountain summit, 3400 m | Continuous |
| Orbiting Infrared Array | 2.4 | Infrared | Orbit, 1.5 million km from Earth | Not possible |
15 Complete each of the three statements below by placing an X in the box next to the phrase that correctly completes the statement. [1]
16 Several statements about the atmospheric transmission graph are listed below.
Statement 1: The atmosphere blocks nearly all radiation with wavelengths shorter than 3 × 102 nm.
Statement 2: The atmosphere blocks nearly all radiation in the visible band.
Statement 3: A wide window near 1 × 108 nm allows ground-based detection of radio waves.
Statement 4: Most mid-infrared radiation from space reaches Earth's surface unabsorbed.
Statement 5: Water vapor and carbon dioxide absorb much of the infrared radiation arriving from space.
Statement 6: Radiation is blocked by the atmosphere equally at every wavelength.
Which statements are correctly supported by the graph?
17 Which row in the table below correctly describes how a telescope's performance changes when its aperture is increased from 0.6 m to 2.4 m?
| Row | Light-Gathering Power | Amount of Detail Resolved | Faintest Object Detectable |
|---|---|---|---|
| (1) | 4 times greater | Increases | Fainter |
| (2) | 16 times greater | Increases | Fainter |
| (3) | 16 times greater | Decreases | Brighter |
| (4) | 4 times greater | Decreases | Brighter |
18 A team recorded the following observations of an unidentified source.
A. The source does not appear in any visible-light image.
B. The source is brightest at a wavelength of 1 × 104 nm.
C. The source is embedded in a thick cloud of cold dust.
D. The source emits strongly at 1 × 10−1 nm.
E. The source is located outside the Milky Way galaxy.
F. The source has a surface temperature above 25,000 K.
Which set of observations correctly identifies the instrument the team should use?
Before committing funds, the team compared the benefits and drawbacks of each design. Some of this information is shown in the chart below.
| Advantages | Disadvantages | |
|---|---|---|
| Ground-based optical | • Lower construction cost • Can be repaired and upgraded continuously • Larger apertures are practical |
• Limited to visible and radio windows • Skyglow from nearby towns raises background • Image blurred by air turbulence • Dust blocks visible light from star-forming regions |
| Space-based infrared | • No atmospheric absorption of infrared • No skyglow or turbulence • Infrared passes through dust clouds • Cooled optics reduce background heat |
• Very high development and launch cost • Repair is not possible at this distance • Limited operational lifetime (coolant, fuel) • Smaller aperture than the largest ground telescopes |
19 A student claims that the space-based infrared telescope is the more effective design solution for imaging stars forming inside the dust cloud. Using all the information provided, which statement provides the most correct evidence to support this claim?
20 Choose the correct letter to complete each statement about telescope design. [1]
Choices for Statement 1:
A – eliminate chromatic aberration and allow a larger aperture to be supported from behind
B – eliminate chromatic aberration but limit the aperture, because the glass must be flawless throughout
Choices for Statement 2:
C – reduce absorption by atmospheric water vapor and reduce the heat radiated by the instrument itself
D – reduce absorption by atmospheric water vapor but increase the heat radiated by the instrument itself
Choices for Statement 3:
E – reduce skyglow and improve detection of faint visible-light objects
F – reduce skyglow but prevent detection of faint infrared objects
21 Using ESRT page 14, rank the four forms of radiation below in order of increasing photon energy. Tap a card, then tap the position where it belongs. Then justify your ranking. [1]
Justification (refer to wavelength and frequency):
22 A student makes the following claim:
Place an X in either the Support or Refute box to indicate whether the information provided supports or refutes the claim. Then justify your response using evidence. [1]
No single telescope can observe the entire electromagnetic spectrum. Engineers select an aperture, a detector, and a site based on the wavelength the science target emits. The table below lists five operating or recently retired observatories and the wavelength each was designed to record.
| Observatory | Aperture | Design Wavelength (nm) | Site | Signature Result |
|---|---|---|---|---|
| W. M. Keck Observatory | 10 m (×2) | 5.5 × 102 | Mauna Kea summit, 4145 m | Tracked stars orbiting the Milky Way center |
| Very Large Array (VLA) | 27 dishes, 25 m each | 1.0 × 108 | Plains of San Agustin, New Mexico | Imaged a planet-forming disk around a young star |
| Hubble Space Telescope | 2.4 m | 2.0 × 102 | Orbit, 535 km above Earth | Hubble Deep Field survey of distant galaxies |
| James Webb Space Telescope | 6.5 m | 1.0 × 104 | Orbit, 1.5 million km from Earth | Detected galaxies formed soon after the Big Bang |
| Kepler Space Telescope | 0.95 m | 6.0 × 102 | Solar orbit, trailing Earth | Confirmed more than 2700 exoplanets by transit dips |
Use ESRT page 14 and the atmospheric transmission graph to complete every cell.
| Observatory | Design Wavelength (nm) | ESRT p. 14 Band | In an Atmospheric Window? |
|---|---|---|---|
| Keck | 5.5 × 102 | ||
| Very Large Array | 1.0 × 108 | ||
| Hubble | 2.0 × 102 | ||
| James Webb | 1.0 × 104 | ||
| Kepler | 6.0 × 102 |
23 A newly discovered object is buried inside a cold dust cloud and radiates most strongly at 1.2 × 104 nm. Which observatory in the table is best suited to study it, and why?
24 Kepler observed at 6.0 × 102 nm, a wavelength that lies inside an atmospheric window, yet it was still launched into solar orbit. Which row in the table below correctly identifies the design reason and the measurement it protected?
| Row | Reason for Placing Kepler in Space | Measurement Protected |
|---|---|---|
| (1) | The atmosphere absorbs nearly all visible light | Spectral class of each star |
| (2) | Sunlight would overheat a ground-based detector | Surface temperature of each planet |
| (3) | Turbulence, weather, and day-night cycles interrupt ground observations | Continuous, extremely small dips in a star's brightness |
| (4) | Visible light is redshifted into the infrared above the atmosphere | Recessional velocity of each host star |
25 The Very Large Array uses 27 separate dishes spread across baselines up to 36 km rather than one enormous dish. Which statement best explains this design decision?
26 Keck has an aperture more than four times larger than Hubble, yet Keck cannot record the 2.0 × 102 nm radiation Hubble observes routinely. Using evidence from the transmission graph, construct an explanation for this difference. [1]
27 A student claims that the James Webb Space Telescope, not Hubble, is the better instrument for imaging the very first galaxies that formed after the Big Bang. Which statement provides the most correct evidence to support this claim?