Recently, we wrapped up our space series on Patreon with the final chapter in a 5-chapter-series on The Cosmic Ladder. In this series, we explored how to grasp the grandness of the universe by inventing suitable yardsticks for different parts of space. Click here to read all the chapters and to get access to more exclusive space content.
In this post you find a quiz that challenges your knowledge on the cosmic ladder and the different objects we find on various scales in the great universe. You can find all answers in the link – or maybe you already know some of them.
Find out by taking the quiz here!
Click each question to read the answer.
Question 1: What is the cosmic ladder?
The cosmic ladder is a description of the yardsticks we use in space to describe scales across the universe.
It is called a “ladder” because each scale has its own step. One step on the ladder is the solar system. Here we use Astronomical Units (AU) to describe the distance to objects we find on this scale. If we move further up the ladder, we find steps that describe the greater scales such as galaxies and galaxy clusters, where we use units such as light-years or Gigaparsec.
Question 2: What is a standard candle?
A standard candle is -almost as the name reveals- a light source in space that has a standard luminosity, i.e. the amount of light it shines is more or less fixed. We use standard candles to measure distances.
A type Ia supernova is a standard candle because its light curve is known to us, and hence we can measure how dimmed it is in our observations and from that infer how far away the explosion is. Almost like knowing how bright a set of car headlights are and then calculating how far away the car is by measuring how dim the light we can see is.
Standard candles are a key component in our measurement of the size of the universe.
Question 3: Is a parsec bigger or smaller than a light-year?
A parsec is the same as 3.26 light-years so 1 parsec is indeed bigger than 1 light-year.
Question 4: A light-year is defined as the distance that light travels in 1 year. How is a parsec defined?
A parsec is defined from measuring how background stars “move” compared to a nearby reference star when we orbit the sun.
The distance to a nearby star is exactly 1 parsec when the angle at which the background stars “move” is 1 arcsecond during the course of 6 months, i.e. for Earth to make half an orbit around the sun.
Question 5: Can a star die twice?
Small stars die by shredding some of their mass and leaving a white dwarf, and big stars die in supernova explosions.
A supernova is not just a supernova. There are several kinds, the most known is the core-collapse supernovae, where a massive star explodes after having a sufficient build-up of iron in the core. This type is a type IIb/c supernova.
A type Ia supernova happens when a white dwarf, i.e. an already dead star, accretes mass from a companion star. When it reaches a mass of 1.4 solar masses, the so-called Chandrasekhar limit, it “dies again” and explodes in a supernova. It leaves behind a neutron star or black hole.
Because a type Ia supernova always has a mass of 1.4 solar masses, then its light curve is always known, too, and we can use this to calculate distances in space.
Question 6: How far into space can we use standard candles to measure distances?
We can use standard candles such as type Ia supernovae and cepheid variable stars to measure distances up to 1 Giga parsec, i.e. 1 million parsec. At these distances we find galaxy clusters that reside far outside our own Local Group.
The edge of the universe is 14 Gpc away, so standard candles only cover a significant yet small fraction of all there is to measure in space.
Question 7: Is the universe expanding or contracting?
The universe is not only expanding, it is expanding in an accelerating manner!
Dark energy is responsible for this strange behavior, but not much more is known. The expansion of the universe can be observed by observing distant galaxy clusters. A measure of the galaxies’ redshift will reveal that the clusters are moving away from us much faster than they would if the universe was static.
Question 8: Do we use Astronomical Units, AU, to describe distances outside our solar system?
We use AUs to describe the scales of other solar systems, i.e. distant stars with exoplanets around them. An AU is defined from our own solar system but can indeed be used in other systems as well.
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