AST 112 1.4 Notes

Why are astronomical numbers difficult to work with?

Astronomy deals with extremely large distances and numbers far beyond everyday experience.

What two strategies help astronomers handle large numbers?

Scientific notation and the use of consistent SI (metric) units.

What is scientific notation?

A way of writing very large or very small numbers using powers of ten.

Why is scientific notation useful?

It eliminates long strings of zeros and makes numbers easier to read and compare.

How is 500,000,000 written in scientific notation?

5 × 10^8

What does the exponent in scientific notation represent?

The number of places the decimal point is moved.

What unit system do astronomers use?

The International System of Units (SI), also known as the metric system.

Why is the SI system important in astronomy?

It provides consistency when measuring and comparing quantities.

What is a light-year?

The distance light travels in one year.

Why is light a good standard for measuring distance?

Light travels at a constant speed and is the fastest possible speed in the universe.

Why is a light-year a distance and not a time?

It measures how far light travels in a year, not the passage of time itself.

What everyday example mixes time and distance?

Saying a place is “20 minutes away.”

What is the speed of light in kilometers per second?

3 × 10^5 km/s

How many kilometers are in one light-year?

9.46 × 10^12 kilometers.

How far away is the nearest star (other than the Sun)?

About 4.25 light-years away.

How far away are many visible stars?

Hundreds to thousands of light-years away.

How far away is the Orion Nebula?

About 1,400 light-years.

How many kilometers away is the Orion Nebula?

Approximately 1.34 × 10^16 kilometers.

What is the Orion Nebula made of?

Gas and dust from which new stars and planets are forming.

What illuminates the Orion Nebula?

Light from extremely energetic young stars.

How can large distances be visualized?

A string one light-year long could wrap around Earth about 236 million times.

How is 79.2 billion written in scientific notation?

7.92 × 10^10

Why is scientific notation common in astronomy examples?

Astronomical values are often extremely large.

How many seconds are in one hour?

3.6 × 10^3 seconds.

How many hours are in one year?

About 8.77 × 10^3 hours.

What key idea do light-year calculations demonstrate?

Even the nearest stars are incredibly far away.