Milky Way The Sun is a star in the Milky Way galaxy. When viewed from the side, the galaxy looks

Milky Way The Sun is a star in the Milky Way galaxy. When...

Key Concepts

Light-year

A light-year is a unit of distance used in astronomy that represents the distance light travels in one year through a vacuum. It is essential for expressing the vast distances between celestial objects and can be converted into other units such as meters, kilometers, and miles using well-defined conversion factors.

Unit Conversion

Unit conversion is the process of converting a measurement from one unit to another using conversion factors. In astronomy and physics, this is crucial for translating astronomical distances, which are often given in light-years or astronomical units, into more familiar units like meters or miles for easier interpretation and comparison.

Scientific Notation

Scientific notation is a method of expressing very large or very small numbers in a compact form by using powers of ten. This is particularly useful in astronomy where distances and other measurements are enormous, simplifying calculations and ensuring clarity and precision in communication.

Astronomical Distance Measurement

Astronomical distance measurement involves techniques and units specifically designed to handle the immense scales in the universe, such as light-years, parsecs, and astronomical units. Understanding these measurements and how to convert between them is fundamental for studying and interpreting the structure and dynamics of the cosmos.

Transcript

0:00 Hello everyone.

00:01 This is the solution to problem 20 of chapter 24 of college physics.

00:06 For the first part here, we're asked to find what the distance or the diameter of the milky way is when written in terms of meters, kilometers, and miles, and then we're asked to do the same for the milky way's thickness.

00:23 Now, what is a light year in meters? this is the first thing we have to work out, we are told that the milky way has a diameter that is a hundred thousand light years.

00:41 So just write this as 10 to 5.

00:45 And so we have to convert the light years to meters first.

00:53 Now i'm not going to do this explicitly, but i'm just going to tell you what the conversion vector is.

00:58 And so first for that, we're going to work out what one light year is.

01:02 Now one light here, we're told, is the distance that light travels in a year.

01:08 So knowing that the speed of light is three times 10 to 8 meters per second, we know that this is 3 times 10 to the 8 times the time there is in a year in seconds.

01:28 So what is that? so this is going to be 365 for the number of days.

01:34 Times 24 for the number of hours, times 60 for the number of minutes in an hour, and then times 60 again for the number of seconds in an hour.

01:47 And so this is one year in seconds.

01:57 And so you multiply this vector onto c or the speed of light, and that's how you get the distance of one light year.

02:05 Now, then knowing that this is what one light year is, and knowing that the diameter is 10 to 5 light years, we can just substitute it back in here, and we're going to get 10 to 5 times 3 .00 times 10 .38 times this factor of one year in seconds.

02:30 So 3, 6, 5 times 24 times 60 times 60.

02:41 And so this is going to give us that the diameter of the milky way in terms of meters is 9 .46 times 10 to the 20 meters.

02:59 So this is the diameter of the milky way written in terms of meters...

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