Chapter 2: Time and Space Flashcards
What is a light-year?
A light-year is the distance that light travels in one year, approximately 9.46 trillion kilometers (9.4608 × 10¹² km).
What major discoveries did Galileo Galilei make with his telescope?
Galileo (1546-1642)
- Galileo was first to observe planets through a telescope
- did not invent the telescope but improved it
- magnified 8 fold, and in a later instrument 33 fold
1609-1610 made revolutionary discoveries using the 8 fold telescope:
discovered the Moon’s surface features, sunspots, and four moons of Jupiter, supporting the heliocentric model.
Considered himself a Copernican and was told to stop teaching this by the church - he stopped teaching it but not arguing it!
He was charged for heresay - the Inquisition placed him under house arrest
Why are light-years used to measure distances in space?
Light-years are used because distances in space are so vast that measuring in kilometers or miles would be unwieldy
How far is the nearest star from the sun in light years?
How far away from the sun is the farthest naked eye object?
Proxima Centauri, the nearest star to the Sun, is 4.3 light-years away.
The Andromeda galaxy is farthest naked-eye object – 2.36 million light years from the sun
What are the closest planets to the sun (those measured in light minutes)
- Mercury (3.22 light mins)
- Venus (6.01 light mins)
- Earth (8.32 light mins)
- Mars (12.7 light mins)
- Jupiter (43.3 light mins)
Which planets are further away from the sun (those measured in Light hours)
- Saturn (1.32 Light hours)
- Uranus (2.66 liht hours)
- Neptune (4.16 light hours)
How far away is the centre of the Milky Way from the Sun?
26 thousand light years
Why is observing the light from stars like seeing into the past?
if a star is 1 million light years away, it means the light has taken 1 million years to reach you - therefore, you are seeing light from 1 million years ago, not seeing it as it is now - lots of things could have happened in those 1 million years that we can’t see because the light has not reached us
What are the methods for measuring different ranges of distances in space
different measurements are needed for different distance ranges
up to 500 light years distance
* Trigonometric Parallax
500 to 500 million light years distance
* Main Sequence Fitting (up to 150,000 Light years)
* “Marker Stars” - Cepheids (up to 500 million light years)
more than 500 million light years distance
* Hubble’s Equation
Explain the use of trigonometric Parallax to measure distances in space
Useful range?
What is this Method about?
Steps?
Info needed for the calculation?
Useful Range: Distances up to 500 light years
Method: Trigonometric Parallax
What is this method about?
* an object appears to be at a different place relative to the background, depending on your viewpoint
* involves measuring the apparent shift in position of a nearby star against distant stars as Earth moves around the Sun.
Steps:
1. Astronomers view a star centered to middle of telescope
2. Astronomers view that star again at a different time (from 2 different viewpoints in Earth’s orbit)
3. The nearby star appears to “wobble” against the background of distant stars.
4. Parallax Angle: The angle of this wobble (called the parallax angle) is measured.
- the angle at which we would have to move our telescope to recenter the start
5. Distance Calculation: Knowing the Earth’s orbital distance (300 million km, or 2 astronomical units), astronomers use geometry to calculate the star’s distance.
Info needed for the distance calculation:
* Parallax angle
* Earth’s orbital distance (2AU or 300 mill km)
Describe the Image Below
**This image represents parallax **- scientists use this to measure distances up to 500 light years.
For example, they measure the apparent position of the nearby star against a background of distant stars from one position in earth orbit in July
6 months later, in January, the Earth is at a different position in orbit (half way around) and they measure again the nearby star against a background of the distant stars.
The nearby star appears to be in a different position. the parallax angle p’’ is measured – this is the angle that we woud have to readjust the telescope to recentre the nearby star after the apparent change in position – this is a very small angle
distance is represented by d – we must know the distance Earth has travelled in these 6 months (2 AU)
using the parallax angle and the distance earth has travelled in its orbit, we can caluclate the distance of the star from earth
How can you explain parallax in an easy way using a finger test?
hold your finger up, close one eye and align finger with some distant object
now switch eyes - close eye and open the other
Your finger appears to have changed positions relative to the background
This is because you changed the viewpoint (which eye seeing it from)
Explain the use of the Hertzsprung-Russel Diagram (Main Sequence Fitting) to measure distances in Space.
Useful range?
What is this method about?
Steps?
Formula?
Useful Range:Up to 150,000 Light Years Distance
Method: Main Sequence Fitting using Hertzsprung-Russel Diagram
What this method is about:
* relating the luminosity (brightness) of stars to their temperature (related to color)
Steps:
1. use a calibrated colour chart to determine temperature value (because temp is related to color)
2. Determine apparent brightness through observation
3. Use H-R diagram to find star’s intrinsic brightness for temperature value (draw vertical line from temperature to main sequence and horizonal from mainsequence to luminosity to get instrinstic brightness value)
4. Compare apparent brightness to intrinsic brightness using the equation
FORMULA
Define Luminosity of a star
Define Apparent Brightness and how you find it
Define Instrinsic Brightness and how you find it
Exlain how you find temperature of a star?
Luminosity = Brightness
Apparent Brightness: Brightness we see from Earth through observation
Intrinsic Brightnesss: True brightness found from sequence fitting (the brightness we find by using the temp of the star to draw a line to main sequence, then a line to luminosity)
You can find the temperature of a star with a calibrated colour chart because color and temperature are related.
Explain the use of “marker stars” called cepheids to measure distances in space
Useful Range?
What is the Method about?
Steps?
Formula?
Useful Range: up to 500 million light years
Method: Cepheids as marker stars
What this Method is About:
* Using the period-luminosity relationship of cepheid stars to determine their intrinsic brightness
* We use same equation as used in sequence fitting, so we need to know their apparents and intrinstic brightness
Cepheids: Variable stars that have a regular cycle of brightness changes
Period-Luminosity Relationship: The time between brightness peaks (the period) of a Cepheid star is directly related to its intrinsic brightness.
Steps:
1. Measure the time between brightness peaks to determine the star’s intrinsic brightness.
2. Determine the apparent brightness through observation
3. Use the same brightness-distance calculation as main-sequence fitting.
FORMULA
Describe the use of Hubble’s Law to measure distances in Space:
Useful Range: more than 500 million light years– primarily used for galaxies, clusters of galaxies, and quasars that are extremely far away.
Method: Hubble’s Law
**What is this Method About? **
* using the redshift of stars and galaxies, and Hubble’s equation to determine their distance
Steps:
1. Measure the redshift to determine velocity
* observe light from galaxy through telescope
* compare to known spectral lines of elements (light patterns emmited by certain elements)
* Then we can calculate how much it has redshifted
* The amount of redshift is directly related to it’s velocity therefore we can determine velocity
2. Calculate the distance using Hubble’s equation
* Hubble’s equation can be simply rearranged to calculate distance (velocity/Hubble’s constant)
* the equation gives distance as (d) measured in parsecs
1 parsec - 3.26 light years
FORMULA
Image of a map of the visible universe. Describe the image and define the virgo supercluster
The Virgo Supercluster is the supercluster of galaxies that includes the Milky Way galaxy, where our solar system resides. It’s one of the many superclusters that make up the observable universe. In the image, it’s highlighted to indicate its location relative to the myriad other galaxies visible.
The line showing the scale of 1 billion light years proves how vast our universe is
What is depicted in this famous photo? How was it taken
This is “deep space” captured by the Hubble Space Telesope many years ago – each of the spots of light in the picture (with the exception of a few close stars) are galaxies
Describe what is depicted in this image
This is an image the depicts our galaxy, the Milky Way
Because the milky way is disc-shaped, the wide band lit by a high density of stars is a view of the milky way.
This is looking parallel to the plane of the disc (perpendiculat view sees relatively few stars)
