E And S Galaxies And Asteroids Flashcards
What is the Milky Way?
The Milky Way is the galaxy where we live, visible as a milky band across the sky on clear nights.
What does the term ‘galaxy’ originate from?
The word ‘galaxy’ comes from a Greek word for ‘milky’.
What shape is the Milky Way?
The Milky Way is a spiral galaxy.
Why does the Milky Way appear as a band across the sky?
We can only see one arm of the spiral from our position within the galaxy.
How many stars are estimated to be in the Milky Way?
There are an estimated 250,000,000 stars in the Milky Way, including our Sun.
What is the Universe?
The Universe describes all of space and everything in it.
What are the different shapes of galaxies?
Galaxies can be classified as elliptical galaxies or irregular galaxies.
What is the closest known galaxy to the Milky Way?
The closest known galaxy to the Milky Way is called the Canis Major. It is elliptical in shape and a distance of 240,000 million million km away from us.
What are galaxies made of?
Galaxies are made from stellar dust, gas, stars, and solar systems held together by gravity. Stellar dust is the dust found in space. The Earth is travelling through a cloud of stellar dust that is estimated to contain one dust particle in every one million m² of space!
How strong is the gravity holding a galaxy together?
The gravity holding a galaxy together is strong because galaxies have very large mass. Even if you could travel at the speed of light (300,000 km/s), it would take you more than 100,000 years to cross from one side of the Milky Way to the other! Scientists estimate the mass of the Milky Way to be 1,500,000,000,000 times the mass of the Sun.
How many galaxies are there in the Universe?
Scientists have counted the galaxies in one part of space and multiplied this number to estimate the total number of galaxies in the Universe. The answer they got was 100,000,000,000 galaxies!
Are the estimates of the number of galaxies accurate?
Such estimates may not be accurate. There could be more or fewer galaxies in the part of space that the scientists counted compared to the rest of the Universe. Also, the scientists may not know the total volume of the Universe accurately.
What are the different shapes of galaxies?
Galaxies can have different shapes, including irregular and elliptical.
What are asteroids?
Asteroids are objects made from rock that orbit the Sun.
What is the size range of asteroids?
Asteroids range in size up to 975 km across. The smallest asteroid that has been studied is 2 m across.
How do scientists describe the shape of most asteroids?
Scientists describe the shape of most asteroids as being similar to the shape of potatoes.
Where do most asteroids in the Solar System orbit?
Most of the asteroids in the Solar System orbit the Sun between the orbits of Mars and Jupiter.
How many asteroids are there?
There are millions of asteroids. Some have been studied and have been given names.
What is the largest asteroid and when was it discovered?
The largest asteroid is called Ceres and was discovered in the year 1801.
What did scientists initially think Ceres was?
When Ceres was discovered, scientists thought it was a new planet.
What term was introduced for Ceres and why?
The term asteroid was introduced because Ceres looked much smaller than a planet.
What features does Ceres have?
Ceres has a core, a mantle, and a crust like some planets.
What are some characteristics of asteroids?
Asteroids are smaller than planets, irregular in shape, and primarily located in a belt between Mars and Jupiter.
What is the size of asteroid Itokawa?
Asteroid Itokawa is about 530 m long and about 250 m wide.
When did a spacecraft collect samples from Itokawa?
In the year 2005.
What have studies of Itokawa’s samples provided evidence for?
They have given scientists more evidence about how the Solar System formed.
What is Itokawa primarily made of?
Itokawa appears to be made from lumps of rock.
Where do the lumps of rock on Itokawa likely come from?
They appear to have come from other small planets or moons which have been broken by impacts.
Why is the force of gravity on Itokawa weak?
The asteroid is a relatively small object.
What can change the shape of an asteroid like Itokawa?
Tidal forces when it passes a large object such as a planet.
How do scientists know some asteroids are made from a single piece of rock?
These asteroids are small and spin quickly.
What is the average frequency of large asteroid impacts on Earth?
Scientists think a large asteroid impacts the Earth on average every 130,000 years.
How frequently do smaller asteroids impact Earth?
Smaller asteroids impact the Earth very frequently.
What happens to many small asteroids in the Earth’s atmosphere?
Many small asteroids break up and never reach the surface.
What are the two reasons why asteroids impact with Earth?
- The Earth exerts a strong force of gravity on passing objects such as asteroids.
- Many asteroids have orbits that pass relatively close to Earth.
What is the term for a three-dimensional shape that curves around a central axis?
Spiral
What is a common characteristic of a spiral structure?
It has a continuous and gradually widening shape.
What is an example of a irregular in nature?
The shape of a galaxy, such as the Large Magellanic Cloud.
Example: The Large Magellanic Cloud is a irregular galaxy.
