1
00:00:00,160 --> 00:00:02,760
Speaker 1: Streaming TV shows and movies directly to your home is

2
00:00:02,759 --> 00:00:05,560
Speaker 1: a breeze with Netflix. As a Netflix member, you can

3
00:00:05,600 --> 00:00:09,040
Speaker 1: instantly watch TV and movies on your PC, Mac, mobile device,

4
00:00:09,160 --> 00:00:12,440
Speaker 1: or television. Get a free thirty day trial membership. Go

5
00:00:12,520 --> 00:00:15,200
Speaker 1: to Netflix dot com slash stuff and sign up today.

6
00:00:15,880 --> 00:00:18,919
Speaker 1: Welcome to brain Stuff from how Stuff works dot com

7
00:00:18,920 --> 00:00:30,120
Speaker 1: where smart happens. Hi. I'm Marshall Brain with today's question,

8
00:00:30,640 --> 00:00:34,199
Speaker 1: what is a light year? A light year is a

9
00:00:34,240 --> 00:00:37,600
Speaker 1: way of measuring distance that doesn't make much sense because

10
00:00:37,760 --> 00:00:41,000
Speaker 1: light year contains the word year, which is normally a

11
00:00:41,120 --> 00:00:45,400
Speaker 1: unit of time. Even so, light years measure distance. When

12
00:00:45,440 --> 00:00:49,480
Speaker 1: astronomers use their telescopes to look at stars, the distances

13
00:00:49,520 --> 00:00:53,479
Speaker 1: are gigantic. For example, the closest start of Earth besides

14
00:00:53,520 --> 00:00:57,480
Speaker 1: our sun is something like twenty four trillion miles or

15
00:00:57,560 --> 00:01:02,639
Speaker 1: thirty eight trillion kilometers away. That's the closest star. There

16
00:01:02,680 --> 00:01:05,640
Speaker 1: are stars that are millions of times further away than that.

17
00:01:06,160 --> 00:01:09,160
Speaker 1: When you start talking about those kind of distances, a

18
00:01:09,200 --> 00:01:12,560
Speaker 1: mile or kilometer just isn't a practical unit to use

19
00:01:12,840 --> 00:01:15,920
Speaker 1: because the numbers get too big. No one wants to

20
00:01:15,959 --> 00:01:19,000
Speaker 1: write or talk about numbers that have twenty digits in them.

21
00:01:19,480 --> 00:01:22,920
Speaker 1: So to measure really long distances, people use a unit

22
00:01:22,959 --> 00:01:26,280
Speaker 1: called a light year. Light travels at a hundred eighty

23
00:01:26,400 --> 00:01:30,399
Speaker 1: six thousand miles per second or three hundred thousand kilometers

24
00:01:30,400 --> 00:01:34,720
Speaker 1: per second. Therefore a light second is a hundred eighty

25
00:01:34,760 --> 00:01:38,319
Speaker 1: six thousand miles or three hundred thousand kilometers. A light

26
00:01:38,600 --> 00:01:41,959
Speaker 1: year is the distance that light can travel in a year,

27
00:01:42,640 --> 00:01:47,400
Speaker 1: or roughly six trillion miles or ten trillion kilometers. That's

28
00:01:47,440 --> 00:01:50,800
Speaker 1: a long way, so the closest star is about four

29
00:01:51,000 --> 00:01:55,280
Speaker 1: light years away. Using a light year as a distance

30
00:01:55,360 --> 00:01:59,480
Speaker 1: measurement has another advantage. It helps you determine age. Let's

31
00:01:59,520 --> 00:02:02,080
Speaker 1: say that a star is a million light years away.

32
00:02:02,360 --> 00:02:05,240
Speaker 1: The light from that star has traveled at the speed

33
00:02:05,280 --> 00:02:08,400
Speaker 1: of light to reach us. Therefore, it's taken the star's

34
00:02:08,520 --> 00:02:11,080
Speaker 1: light one million years to get here, and the light

35
00:02:11,200 --> 00:02:14,880
Speaker 1: we're seeing was created one million years ago. So the

36
00:02:14,960 --> 00:02:17,800
Speaker 1: star we're seeing is really how the star looked a

37
00:02:17,840 --> 00:02:20,800
Speaker 1: million years ago, not how it looks right now. In

38
00:02:20,840 --> 00:02:23,840
Speaker 1: the same way, our sun is eight or so light

39
00:02:24,040 --> 00:02:28,160
Speaker 1: minutes away. If the sun were to suddenly explode right now,

40
00:02:28,639 --> 00:02:31,359
Speaker 1: we wouldn't know about it for eight minutes, because that's

41
00:02:31,400 --> 00:02:33,120
Speaker 1: how long it would take for the light of the

42
00:02:33,160 --> 00:02:38,040
Speaker 1: explosion to get here. For more on this and thousands

43
00:02:38,080 --> 00:02:40,680
Speaker 1: of other topics, does that how stuff works dot Com

44
00:02:40,720 --> 00:02:42,600
Speaker 1: and don't forget to check out the brain stuff blog

45
00:02:42,680 --> 00:02:44,840
Speaker 1: on the house stuff works dot com home page. You

46
00:02:44,840 --> 00:02:47,799
Speaker 1: can also follow brain stuff on Facebook or Twitter at

47
00:02:47,800 --> 00:02:52,560
Speaker 1: brain stuff hs W. The house Stuff Works iPhone app

48
00:02:52,600 --> 00:02:59,440
Speaker 1: has arrived down at it today on iTunes. This episode

49
00:02:59,440 --> 00:03:01,280
Speaker 1: of brain stuf Off is brought to you by Linda

50
00:03:01,320 --> 00:03:04,680
Speaker 1: dot Com. Linda dot Com offers thousands of engaging, easy

51
00:03:04,680 --> 00:03:07,840
Speaker 1: to follow video tutorials taught by industry experts to help

52
00:03:07,880 --> 00:03:11,360
Speaker 1: you learn software, creative and business skills. Membership starts at

53
00:03:11,360 --> 00:03:14,800
Speaker 1: twenty five dollars a month and provides unlimited seven access

54
00:03:14,960 --> 00:03:17,560
Speaker 1: Tried Linda dot Com free for seven days by visiting

55
00:03:17,639 --> 00:03:19,720
Speaker 1: Linda dot com slash brain Stuff