P7 - Further Physics - Studying the Universe

Question 1

What is 1’ arc minute?

(1’ minute of arc)

Answer 1

1/60*1^o.

Question 2

How are stars formed?

Answer 2

1. Gravity brings gas clouds together, causing them to become denser.
2. The force of gravity pulls the gas inwards, causing the pressure and temperature to increase.
3. As more gas is drawn in, the force of gravity increases.
4. The gas is compressed further, becomes hotter and denser, and forms a protostar.
5. Eventually, the temperature and pressure become so high that hydrogen nuclei fuse into helium nuclei. Energy is released and the star is a main sequence star.

Question 3

What is retrograde motion?

Answer 3

Where planets appear to slow down against the star background and go in reverse.

This happens because the Earth’s smaller orbit causes it to overtake the outer planets at different times of year.

A good example is Venus, which looks like it travels in one direction when on the same side of the Sun as Earth, but the opposite direction if it’s on the other side to Earth.

See this video to visually explain this concept.

Question 4

How long does it take for the Moon to orbit the Earth?

Answer 4

About 27 days.

Question 5

What is 1’’ arc second?

(1’’ second of arc)

Answer 5

1/60*1’ or 1/3600.

Question 6

What are the properties of diffraction?

Answer 6

• None of the properties change apart from the direction in which the wave is travelling.

Question 7

Draw the Lifecycle of a Star.

Answer 7

Question 8

Give advantages and disadvantages to locating astronomical observatories on isolated high mountains.

Answer 8

_Advantages *(Any of the following)*:_

• Away from any light pollution.
• Low atmospheric pollution.
• Less scattering of light.
• Dry air/less humid.
• Frequent cloudness lights/above the clouds.
• Less atmospheric absorption.
• Less atmospheric refraction.
• Darker skies give more contrast.
• Less image distortion/flickering.

_Disadvantages *(Any of the following)*:_

• Still some atmospheric absorption.
• Still some atmospheric refraction.
• Some parts of em spectrum absorbed by atmosphere.
• Altitude sickness/difficult working conditions.
• Hard to get to location.
• Higher construction/transport costs.
• Poor transport links.
• Environmental and social impacts.

Question 9

You are given the following formula. What are the units?

Speed of recession = Hubble constant * Distance.

Answer 9

Speed of recession (km/s) = Hubble constant (s^-1) * Distance (km).

AND

Speed of recession (km/s) = Hubble constant (km s^-1 Mpc^-1) * Distance (Mpc).

N.B: -1 means per. For example, km s-1 Mpc-1 means kilometers per second per megaparsec.

Question 10

State two major ground-based optical telescopes.

Answer 10

• Royal Observatory, UK.
• Mauna Kea Observatories, Hawaii.

Question 11

There is a relationship between cepheid period (days) and absolute brightness (lux) - what is this?

Answer 11

Henrietta Leavitt’s graph showing as the period increases, absolute brightness increases.

Question 12

What are the ways we can calculate the distance of stars?

Answer 12

We can either use red shift to calculate the velocity of recession (km/s) and therefore the distance using Hubble Law’s graph.

OR

We can use a parallax distance (Convert from parsecs to megaparsecs). That’s it! We could also use Hubble Law’s graph though, to get the velocity of recession (km/s).

OR

We can calculate the period of luminosity from a cepheid, then calculate the absolute brightness through Henrietta Leavitt’s graph and then use the equation Distance+Apparent Brightness=Absolute Brightness (You will need the apparent brightness, and rearrange the equation).

Question 13

What is a virtual image?

Answer 13

The image formed when light rays from an object appear to have come from another point. e.g: A mirror. The image can not be captured on a screen, as the light waves never cross.

Question 14

What are the 5 steps to drawing a ray diagram?

Answer 14

1) Draw the first ray line from the top of the object to the lens. Then, carry it through the focus.
2) Draw the second ray line from the top of the object through the principal axis (Centre of lens), and carry it on.
3) Draw the third ray line from the top of the object through the focal point on the same side, through to the lens and then horizontally.
4) If the object crosses the principal axis, draw a fourth ray horizontally from the bottom of the object parallel to the principal axis. Then, at the lens, bend the ray towards the focal point on the opposite side.

— The 3 rules —

• In parallel, out through focus.
• In through focus, out parallel.
• Straight through vertex.

Question 15

If nuclear fusion only occurs up to iron - how come we have elements with higher masses than iron?

Answer 15

Because when a high mass star’s core is mostly iron, it explodes as a supernova, creating nuclei with masses greater than iron.

Question 16

In the Curtis & Shapley debate - What did Shapley say?

Answer 16

That the nebulae were nearby within the Milky Way, and that the universe contained only one big galaxy.

Question 17

Electromagnetic radiation with a higher frequency will refract more/less?

Answer 17

Electromagnetic radiation with a higher frequency will refract more?

Question 18

What is 1 parsec?

Answer 18

The distance to a star with a parallax angle of one second of arc.

Question 19

What is the purpose of the objective lens?

Answer 19

To form an image, therefore it should have a long focal length (So that the image can go deeper into the eyepiece without losing focus) and large diameter (To gather more light).

This may seem weird, since it means it has little power, but actually using the formula focal length of objective lens/focal length of eyepiece lens, we can see that the bigger the difference, the higher the magnification, and that if the objective lens had the shortest focal length, we would have a negative magnification.

Question 20

Compare nuclear fusion in main sequence stars and red giants.

Answer 20

• Main sequence stars fuse hydrogen to helium.
• Red giants have a contracting core and rising temperature, so helium can fuse to carbon and further reactions to produce heavier nuclei occur.

Question 21

Convert 0^oC to K.

Answer 21

0^oC = 273K.

Question 22

What are the units for pressure?

Answer 22

Pa (N/m²).

Question 23

A lens that is more curved than another lens made from the same material is stronger/weaker in power and has a shorter/longer focal length?

Answer 23

A lens that is more curved than another lens made from the same material is stronger in power and has a shorter focal length?

Question 24

What is a real image?

Answer 24

The image formed when light rays from an object are made to pass through another point. The light rays are actually there and the image can be captured on a screen.

Question 25

To convert **from C^o to K^o**, you **\_\_\_\_\_\_\_\_\_\_** 273.

Answer 25

To convert **from C^o to K^o**, you **add** 273.

Question 26

When **white light** is passed through a **prism**, the light is **refracted**. **\_\_\_\_\_\_\_\_\_** light is refracted the **least**, and **\_\_\_\_\_\_\_\_\_** light is refracted the **most**.

Answer 26

**_red_** light is refracted the **least**, and **_violet_** light is refracted the **most**. This is because the colours that make up white light have **different frequencies and wavelengths**.

Question 27

How do you calculate the **luminosity period of a cepheid**?

Answer 27

**1/Frequency of pulses** ## Footnote *(Not given)*.

Question 28

To convert **from K^o to C^o**, you **\_\_\_\_\_\_\_\_\_** 273.

Answer 28

To convert **from K^o to C^o**, you **subtract** 273.

Question 29

What is **parallax**?

Answer 29

The **apparent motion of an object against a background**. It's actually the **motion of the observer** that **causes the parallax motion of an object**, however.

Question 30

Define **diffraction**.

Answer 30

When waves **move through a narrow gap or past an obstacle**, and **spread out from the edges**.

Question 31

How long does it take for the **Earth rotate 360^o on its west-east axis**? ***_Accurately_**. **What is this called**?*

Answer 31

**23 hours and 56 minutes**. ## Footnote **Sidereal day**.

Question 32

**Red light** has a **\_\_\_\_\_\_\_\_\_\_ wavelength** and a **\_\_\_\_\_\_\_\_\_** **frequency** compared to violet light.

Answer 32

**Red light** has a **_long_ wavelength** and a **_low_** **frequency** compared to violet light.

Question 33

Define **mass**.

Answer 33

The **amount of matter**.

Question 34

How do you calculate **absolute brightness**?

Answer 34

**Distance + Apparent brightness = Absolute brightness.** *(Rearrangeable - not given)*

Question 35

What **evidence of extraterrestrial life** have scientists found?

Answer 35

**None**.

Question 36

What must you have to **confirm a causal link**?

Answer 36

A **mechanism** that explains **how the factor causes the outcome**.

Question 37

What must **astronomical observatories be aware of** in order to be **socially acceptable**.

Answer 37

* **Costs** involved. * **Environmental** and **social impact** nearby. * **Working conditions** for employees and **access**.

Question 38

How big is **1Mpc**?

Answer 38

**1Mpc = 1 mega-parsec = 1 million parsecs**.

Question 39

**Diffraction is at its maximum when...**

Answer 39

**Diffraction is at its maximum when _gap in aperture = wavelength_.** To minimise diffraction, the gap in aperture should be larger than the wavelength.

Question 40

What is **absolute zero**?

Answer 40

**-273^oC / 0^oK**. ## Footnote This is the **point at which particles stop moving altogether**, and have **no more energy to lose**, and the **temperature can not get any lower**.

Question 41

What is a **total solar eclipse**?

Answer 41

When the **moon is directly in front of the Sun**, and **completely obscures the Earth's view of the Sun**, casting a **shadow on the Earth**.

Question 42

What are the **positives** and **negatives** to **Reflecting** telescopes?

Answer 42

**_Positives_** * Chromatic aberration does **_not_** occur. **_Negatives_** * **Many designs** - different positioning and function of secondary mirror.

Question 43

Give **4 examples** of **major astronomical observatories**.

Answer 43

* **Hawaii**. * **Australia**. * **Chile**. * **Canary Islands**.

Question 44

How is **global success** important in **astronomy**?

Answer 44

**_Share the cost_** * **Expensive**. e.g: **The Great Canary Telescope of 2009**, funded by **Spanish Government, Mexico and Florida**. **_Share expertise_** * Work **faster**, more **efficiently** and share **ideas**. **_Global access_** * Astronomers can book time on telescopes in different countries, allowing them to **see the stars on the other sides of the Earth**.

Question 45

**Hubble law** and **cepheids** both rely on **different factors** - what are these?

Answer 45

**Hubble law** depends on **cepheid variable distances**. _Explanation:_ The **Hubble Constant** is accurately calculated because we know how far away the cepheid variable stars are. **Cepheid variable distances** depend on **parallax distance**. _Explanation:_ We can use **cepheid variable distances when we can't use parallax**. Also, some scientists have tried to combine marginal measurements of many Cepheids to derive an **"average" parallax**.

Question 46

How can we **tell what chemical elements a star contains**?

Answer 46

By comparing the **emission spectra of elements** with the **absorption spectra of a star**.

Question 47

**State** and **explain** the **3 main parts of a star**.

Answer 47

* **_Core_** - **Hottest** part of the star where **nuclear fusion** takes place and **energetic photons are released**. * **_Convective zone_** - Where energy in the form of **photons** is **transferred to the surface by convection currents**. * **_Photosphere_** - Where **photons are radiated into space**.

Question 48

**Radiation** is **diffracted by the aperture of a telescope** - how do we **get around this**?

Answer 48

The effect of this is **blurry images**. To make sure images are **sharp**, the **aperture must be much larger than the wavelength of the radiation detected by the telescope**.

Question 49

Draw the **Hertzsprung-Russell Diagram**.

Answer 49

Question 50

Define **reflection**.

Answer 50

When a **wave bounces from the surface of an obstacle**.

Question 51

What are the **positives** and **negatives** to putting **telescopes in space**?

Answer 51

**_Positives_** * Avoid **atmospheric absorption/reflection/distortion**. * Can **use parts of spectrum that atmosphere absorbs**. **_Negatives_** * Lots of **money** to set up, maintain and repair. * **Uncertainties** of space program.

Question 52

What do astronomers use to get **spectrums from stars**?

Answer 52

A **spectrometer**.

Question 53

A **large or hot star** will burn **_bright/dim_**?

Answer 53

A **large or hot star** will burn **_bright_**. *Therefore, further stars may appear brighter.*

Question 54

What is a **lunar eclipse**?

Answer 54

When the **Earth is between the Sun and the Moon**. This results in the **Earth casting a shadow on the Moon**.

Question 55

What **features** do **major astronomical obervatories** have?

Answer 55

* **Little rain** *(Avoid defraction from rain)*. * **High elevation** *(To avoid atmospheric distortion)*. * **Frequent cloudless nights** *(To see stars clearly)*. * **Low atmospheric pollution + dry air** *(To see stars clearly)*. * **Low light pollution** *(Darker skies provide more contrast)*. * **Equitorial location** *(Best view of solar eclipses)*. * Less scattering of light. * Less image distortion/flickering.

Question 56

What is an **extrasolar planet**?

Answer 56

A **planet that orbits a star other than the Sun**.

Question 57

Define **refraction**.

Answer 57

When **waves cross a boundary between one medium and another**.

Question 58

What is a **solar eclipse**?

Answer 58

When the **Moon passes between the Earth and the Sun**, causing a **shadow on Earth**.

Question 59

How long does it take for the **Earth rotate 360^o on its west-east axis**? *Roughly. **What is this called**?​*

Answer 59

**24 hours**. ## Footnote **Solar day**.

Question 60

If the **Moon orbits the Earth approximately every month**, why don't **eclipses occur every month**?

Answer 60

Because the **moon doesn't orbit on the same plane as Earth** - it has a **5^o inclination** to that of the Earth. Therefore, eclipses only occur when the Moon passes through the **ecliptic** *(The apparent path the Sun traces out along the sky)*.

Question 61

What does a **stars luminosity depend on**?

Answer 61

* **Size**. * **Temperature**.

Question 62

What are the **positives** and **negatives** to **refracting telescopes**?

Answer 62

**_Positives_** * One **basic design**. **_Negatives_** * **Chromatic aberration** occurs *(That weird RGB thing that looks quite cool actually)*. * **Expensive at large sizes**. * Some of the light **reflects off the lens**, so the **image is very faint**.

Question 63

**Why** do we use **computers in telescopes**?

Answer 63

* Work **remotely**. * **Continuous tracking** of astronomical objects. * **Precise positioning** towards astronomical objects. * **Storage** and **processing** of data.

Question 64

In the **Curtis & Shapley debate** - what did **Curtis** say?

Answer 64

That **nebulae were made up of many stars**, and that the **universe consisted of many galaxies like our own**, and that **fuzzy objects were distant galaxies**. He was **correct**. This was proven by **improved telescopes** and the fact that Edwin **Hubble observed Cepheid variables** in one nebula, and found that the **nebula was much further away than any star in the mily way**.

Question 65

What is a **parsec**?

Answer 65

The **distance to a star** with a **parallax angle of one second of an arc**.

Question 66

Why does the **moon** turn **red** during a **lunar eclipse**?

Answer 66

Because the **atmosphere filters out the green to violet range of the spectrum**, letting the **red light pass through**. Also, the Earth's atmosphere **refracts the light** so that it is bent slightly, and can **illuminate the moon at the greatest eclipse** *(The instant when the axis of the Moon's shadow passes closest to the center of Earth)*.

Question 67

What is **Declination**?

Answer 67

**Declination** is like **latitude**, it reports how far away a star is from the **celestial equator**. * A **positive declination** is visible from the **northern hemisphere**. * A **negative declination** is visble from the **southern hemisphere**. You should also be aware that **right ascension** is the **angular distance measured along the celestial equater**. It is **measured in hours**.

Question 68

Write a **sequence of equations** to **explain how Helium (4,2) is formed**.

Answer 68

Question 69

What does a **stars observed intensity** depend on?

Answer 69

* **Luminosity** *(Actual brightness)*. * **Distance from Earth**.

Question 70

What are the **properties** of **reflection**?

Answer 70

* **None of the properties change** apart from the **direction in which the wave is travelling** *(Inverted, \> becomes \< ORA)*.

Question 71

What is **angular magnification**?

Answer 71

The **increase in the angle of an object**, which makes it seem **larger than it actually is**. This is **due to refraction of light**.

Question 72

Define **volume**.

Answer 72

A **3D amount of space**.

Question 73

What are the **properties** of **refraction**?

Answer 73

* The **frequency remains the same**. * There is a **change in wavelength**. * Consequently, there is a **change in wave speed**. * Consequently, there is a **change in direction**.

Question 74

**Describe** the **journey of light** in a **refracting** telescope.

Answer 74

1. Light enters through the **objective lens**, which is usually a **convex lens**. 2. Light is **defracted** slightly. 3. Light hits the **eyepiece lens**, which is usually a **concave lens**. 4. The image is **magnified**. 5. Light hits the **users eye**.

Question 75

Why is a **sidereal day** shorter than a **solar day**?

Answer 75

Because the Earth also orbits the Sun, this **orbiting movement** is the cause.

Question 76

**Describe** the **journey of light** in a **reflecting** telescope.

Answer 76

1. Light enters and hits the **rear primary mirror**, which is the **"objective lens"**, and is usually a **concave _mirror_** to allow more light collection. 2. Light is **defracted** slightly. 3. Light hits the **secondary mirror**, which is the **"eyepiece lens"**, and is usually a **diagonal _mirror_**. 4. Light hits the **eye of the user**.

Question 77

What are the **units** for **volume**?

Answer 77

**m³**.

Question 78

What are the **units** for **mass**?

Answer 78

**kg**.

Question 79

Define **pressure**.

Answer 79

The **force per unit area on the walls of its container**.

Question 80

How can we **measure absolute brightness** from **parallax**?

Answer 80

1. Perform **parallax**. 2. Get the **distance** to a star. 3. Measure the stars **apparent brightness**. 4. **Distance+Apparent brightness=Absolute brightness**!

Question 81

......What **causes** the **emission of radiation of different frequencies** *(Line spectra)*?

Answer 81

The **movement of electrons within an atom.** Electrons can **gain energy to move to a higher energy level**, and will then **release light of one wavelength when they return to the lower energy level**.

Question 82

If you are asked to draw a **graph** *(Oh no...)* showing the **relationship of stars for heat and colours**, what would your **X** and **Y axis** be?

Answer 82

* The **X axis** would be **Wavelength (mm)**. * The **Y axis** would be **Spectral Radiancy/Intensit****y.** Also, I would **start at 3000K** and **go up in 1000K**.

Question 83

What **objects have scientists found in Space that makes it much more likely that extraterrestrial life exists**?

Answer 83

**Planets around other stars**, some of which in **other solar systems**. As well as this, we have found some **planets similar to Earth**.

Question 84

**Describe The Celestial Sphere**.

Answer 84

The **Celestial Sphere** is a **grid for locating stars, relative to the Earth's orbit**. Its **x axis** is **right assention**, measured in **hours**. Its **y axis** is **declination**, measures in **degrees north (+) and south (-)**. **1 hour = 15^o**.

Question 85

What is the **parallax angle**?

Answer 85

**Half the angle** moved against a **background of distant stars** in **6 months**.

Question 86

Good 'ol Jane looks at the **moon** when it is **directly above her**. She then looks in the **same direction again 24 hours later** - but the moon is **not** directly above her. **Why** is this?

Answer 86

Because it **takes longer for the moon to orbit the Earth than it does for the Earth to spin 360^o on its axis**.

Question 87

How can we **prove that light and sound are waves**?

Answer 87

Because they can be **diffracted**.

Question 88

What is the **purpose** of the **eyepiece lens**?

Answer 88

To m**agnify the image formed at the objective lens**. Therefore, we want the **most powerful lens** here, which will have a **short focal length**.