3.4.1Unit 6: Light and objects in space
Galaxies In Space — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions
5 min read 8 parts Lesson 6 of 8 Unit quiz
Lesson summary
3.4.1 Galaxies in space — Notes — CHECKPOINT PHYSICS 0893 notes: Describe galaxies, their shapes and what they are made of, and how scientists estimate how many there are.Name — the galaxy that contains the Earth is called the Milky WayGalaxy — the word comes from a Greek word me…
- Appearance
- Stars we see
- Elliptical
- Stellar dust
- Held together by gravity
- Number of galaxies
Part 1 of 6The Milky Way
Name
- Name the galaxy that contains the Earth is called the Milky Way
Galaxy
- Galaxy the word comes from a Greek word meaning milky
Appearance
- Appearance on a clear dark night a milky band of stars is part of our galaxy
Stars we see
- Stars we see most of the stars seen at night are in our own galaxy
Number
- Number there are hundreds of billions of stars in the Milky Way, including the Sun
Part 2 of 6Shapes of galaxies
Spiral
- Spiral the Milky Way is a spiral galaxy, and from Earth we see one arm as a band across the sky
Elliptical
- Elliptical oval-shaped galaxies
Irregular
- Irregular galaxies without a regular shape
Nearest
- Nearest the closest known galaxy is the Canis Major Dwarf Galaxy, which is elliptical
Part 3 of 6What galaxies are made of
Contents
Contents stellar dust, gas, stars and solar systems
Stellar dust
- Stellar dust the dust found in space, very thinly spread
Held together by gravity
- Held together by gravity galaxies have very large mass, so the gravity holding them is very strong
Size
- Size even at the speed of light it would take more than 100 000 years to cross the Milky Way
Part 4 of 6The universe
Universe
Universe all of space and everything in it
Number of galaxies
- Number of galaxies there are other galaxies besides our own, estimated at about 100 billion
Order of size
- Order of size moon, planet, star, solar system, galaxy, universe
Part 5 of 6Estimating large numbers
Method
- Method count a small sample, measure its mass or volume and scale up to the total
Galaxies
- Galaxies scientists counted the galaxies in one part of space and multiplied up for the whole universe
Uncertainty
- Uncertainty the part counted may have more or fewer galaxies than the rest, and the size of the universe is not known accurately
Sand analogy
- Sand analogy counting a small amount of sand and scaling up by mass or volume models how scientists estimate stars
Part 6 of 6Sand grain estimate
Sand grain estimate
Count a small quantity of sand grains from the large container and put them in the small container.
Repeat to build up a larger counted amount and record the number of grains.
Measure the mass or volume of the grains in the small container.
Measure the mass or volume of all the sand in the large container.
Estimate the total number of grains
Estimate the total number of grains number counted × (large mass ÷ small mass).
Key terms
| Term | Meaning |
|---|---|
| Galaxy | Huge group of stars, gas, dust and solar systems held by gravity. |
| Milky Way | The galaxy that contains the Earth. |
| Universe | All of space and everything in it. |
| Spiral galaxy | Galaxy with arms curving out from the centre. |
| Stellar dust | Dust found in space. |
| Solar system | A star with the objects that orbit it. |
Avoid these mistakes
1
Thinking all the stars in the sky are in other galaxies — most visible stars are in the Milky Way.
2
Thinking the Solar System and the galaxy are the same size — a galaxy contains many solar systems.
3
Thinking the number of galaxies is known exactly — it is an estimate.
4
Confusing galaxy with universe — the universe is all of space and everything in it.
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