## APOD: The Known Universe (2010 Jan 20)

Markus Schwarz
Science Officer
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Location: Germany

### Re: The Known Universe (2010 Jan 20)

Dear Case24,

here are the rough numbers. They are by no means precise, but just orders of magnitude.

diameter earth = 12,700 km
diameter sun = 1.4 10^6 km
So, the diameter would be about 5 m. Imagine your marble and a house.

diameter sun = 1.4 10^6 km
diameter solar system (taken to be that of Pluto's orbit) = 12 10^9 km
So, the diameter would be about 430 m. Imagine a small hill.

diameter solar system (see above) = 11 light hours
diameter of „radio sphere“ = 70 ly
So, the diameter would be about 2.7 km. Imagine a mountain like the Kilimanjaro

diameter of „radio sphere“ = 70 ly
diameter of Milky Way = 30 kpc
So, the diameter would be about 64 m. Imagine a office building.

diameter of Milky Way = 30 kpc
Here I just use the age, since the „size of the universe“ is not well known: 13,7 billion years
So, the diameter would be about 7.6 km. Again, only a mountain comes to my mind.

Chris Peterson
Abominable Snowman
Posts: 18404
Joined: Wed Jan 31, 2007 11:13 pm

### Re: The Known Universe (2010 Jan 20)

Markus Schwarz wrote:diameter of Milky Way = 30 kpc
Here I just use the age, since the „size of the universe“ is not well known: 13,7 billion years
So, the diameter would be about 7.6 km. Again, only a mountain comes to my mind.
The size of the Universe isn't known at all, since most of it is presumably not observable. But the size of the observable Universe is probably known to a high degree of accuracy, and is 93 billion light years. At your scale, that's equivalent to 52 km- quite a bit larger than any mountain.
Chris

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Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

Chris Peterson
Abominable Snowman
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Joined: Wed Jan 31, 2007 11:13 pm

### Re: The Known Universe (2010 Jan 20)

neufer wrote:They couldn't very well include the Kuiper belt after ignoring the Asteroid belt.
The planets are individual, isolated bodies, so you can construct a more or less smooth trajectory from the Sun outwards that will take you past each of them (if you pick a reasonable time). But the asteroid belt, Kuiper belt, and Oort cloud are basically empty space, sparsely populated with tiny bodies. You could construct your path so it took you past one member of each, but that would probably be a rather confusing image to most people, so it makes good sense to leave out these low density clouds of objects.
Chris

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Chris L Peterson
Cloudbait Observatory
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jrsquid3
Asternaut
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Joined: Mon Jan 25, 2010 12:17 am
Location: New York City

### Re: The Known Universe (2010 Jan 20)

FYI, I will be doing this exact "flight" on Tuesday, February 2 at the Hayden Planetarium.

You can RSVP for it here:

or get tickets online here:

http://www.amnh.org/programs/programs.p ... nt_id=1587

TUESDAYS IN THE DOME

VIRTUAL UNIVERSE

The Hayden Planetarium, with ongoing support from NASA, has assembled the world’s largest cosmic atlas, extending from Earth to the greatest distances yet charted by astronomers. Join us on the first Tuesday of each month for a fully interactive tour of the universe that surrounds us—the longest trip you can take while staying in New York.

The Farthest Reaches of the Cosmic Ocean with Jason Kendall
The Farthest Reaches of the Cosmic Ocean with Jason Kendall

* Tuesday, February 2 Buy Tickets
* 6:30 pm
* Hayden Planetarium Space Theater
* \$15 (\$13.50 Members, students, senior citizens)
Enter at 81st Street/Rose Center
* Code: HM020210

Cruise through intergalactic space and explore the immense distances between galaxies. We will learn how the universe has changed with time and how the celerity of light allows us to see the universe as it was billions of years ago.

----

The Museum does this only once a month. If we can sell it out, maybe they'll do more!

Jason Kendall
Director, Inwood Astronomy Project
http://www.inwoodastronomy.org
NASA/JPL Solar system Ambassador, New York City

billcal
Asternaut
Posts: 2
Joined: Mon Feb 01, 2010 11:40 pm

### Re: The Known Universe (2010 Jan 20)

Beautiful video. But in the opening scenes as the "camera" pulls back from the view of the Himalayas, bringing the southern tip of India and then Australia into view, why is the earth shown rotating in the wrong direction (east to west instead of west to east)? When I got up this morning the sun was still rising in the east.

Chris Peterson
Abominable Snowman
Posts: 18404
Joined: Wed Jan 31, 2007 11:13 pm

### Re: The Known Universe (2010 Jan 20)

billcal wrote:Beautiful video. But in the opening scenes as the "camera" pulls back from the view of the Himalayas, bringing the southern tip of India and then Australia into view, why is the earth shown rotating in the wrong direction (east to west instead of west to east)? When I got up this morning the sun was still rising in the east.
Looking at the terminator that is visible in that scene, I don't see anything to suggest the Earth is rotating the wrong way. What happens is that once the camera has pulled back to show the entire Earth, it starts moving to the east (left), which gives a relative apparent east-to-west rotation to the Earth. But it's only an artifact of the viewer's changing position.
Chris

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Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

billcal
Asternaut
Posts: 2
Joined: Mon Feb 01, 2010 11:40 pm

### Re: The Known Universe (2010 Jan 20)

On January 20, without thinking, I posted a comment about the earth appearing to rotate backwards in this video (from east to west instead of west to east as needed to have the sun rise in the east). Almost immediately afterward it dawned on me that this video could only be shot from a satellite traveling eastward around the earth, which would account for the apparent reverse motion. Duhhhh!