# The Size of the Universe in the Hubble Ultra Deep Field Photo

The technical details followed by Chet Raymo's summary of how the photo demonstrates just how incredibly vast is our Cosmos.

Folksonomies: astronomy universe cosmos summary scale hubble photo

# Facts About the Hubble Ultra Deep Field

1. #### 1.How faint are the farthest objects?

The Hubble observations detected objects as faint as 30th magnitude. The faintest objects the human eye can see are at sixth magnitude. Ground-based telescopes also can detect 30th-magnitude objects. Those objects, however, are so dim they are lost in the glare of brighter, nearby galaxies.

Searching for the faintest objects in the Ultra Deep Field is like trying to find a firefly on the Moon. Light from the farthest objects reached the Hubble telescope in trickles rather than gushers. The orbiting observatory collected one photon of light per minute from the dimmest objects. Normally, the telescope collects millions of photons per minute from nearby galaxies.

2.How many orbits did it take to make the observations?

It took 400 orbits to make the observations.

3.How many exposures were needed to make the observations?

The Hubble telescope's Advanced Camera for Surveys' wide-field camera snapped 800 exposures, which equals two exposures per orbit. The exposures were taken over four months, from Sept. 24, 2003 to Jan. 16, 2004.

4.How much viewing time was needed to make all the exposures?

The 800 exposures amounted to about 1 million seconds or 11.3 days of viewing time. The average exposure time was 21 minutes.

5.How many galaxies are in the image?

The image yields a rich harvest of about 10,000 galaxies.

6.How many colors (filters) were used to make the observations?

The colors used were blue, green, red, and near-infrared. The observations were taken in visible to near-infrared light.

7.If astronomers made the Hubble Ultra Deep Field observation over the entire sky, how long would it take?

The whole sky contains 12.7 million times more area than the Ultra Deep Field. To observe the entire sky would take almost 1 million years of uninterrupted observing.

8.How wide is the Ultra Deep Field's slice of the heavens?

The Hubble Ultra Deep Field is called a "pencil beam" survey because the observations encompass a narrow, yet "deep" piece of sky. Astronomers compare the Ultra Deep Field view to looking through an eight-foot-long soda straw.

The Ultra Deep Field's patch of sky is so tiny it would fit inside the largest impact basin that makes up the face on the Moon. Astronomers would need about 50 Ultra Deep Fields to cover the entire Moon.

9.How sharp is Hubble's resolution in pinpointing far-flung galaxies in the Ultra Deep Field?

Hubble's keen vision (0.085 arc seconds.) is equivalent to standing at the U.S. Capitol and seeing the date on a quarter a mile away at the Washington monument.

## Notes:

Interesting factoids about the epic photo that illustrate the scale of the Universe.

Folksonomies: astronomy universe scale hubble galaxies epic

Summary

# Hubble Ultra Deep Field (UDF) photograph

Here we go again, one of the epic documents of our time, the Hubble Ultra Deep Field (UDF) photograph, the deepest look into space ever. A random part of the sky, so small it could be covered by a pinhead held at arm's length. A part of the sky -- as NASA says -- that you'd see looking through an eight-foot-long soda straw. A photo exposed over 400 orbits of the Hubble, a total exposure of 11.3 days. The telescope pointing precisely to the same point in space even as it whizzes around the Earth.

Here's another way to think of it. The image on your computer screen is about 10x10 centimeters. Imagine the image as a tile of that size. A survey of the whole sky -- the whole visible universe from Earth -- would encompass 12.7 million tiles, enough to cover 18 footfall fields!

And each tile shows something like 10,000 galaxies.

A typical galaxy contains as many stars as there are grains of salt in 10,000 one-pound boxes of salt. We are potentially seeing the light of more than 1,000,000,000,000,000 stars. Most, or all, of which have planets.

We've been over this before, but it's worth coming back to. It's not easy to get one's head around. Surely, discovering the scale of the universe is the greatest intellectual achievement in human history, and one of the least appreciated. We live in a universe of at least 10 billion galaxies -- maybe an infinite number -- and we go on worshiping the gods of our cave-dwelling ancestors. Gods with human faces, human qualities, human actions.

Perfectly natural to do so. The familiar is always more consoling than the unfamiliar. As for myself, I stare into those vast and almost unimaginable depths of space and I'm humbled into silence. Stunned. Ecstatic. Curious. Proud of what we have discovered. Knowing that future generations will consider our knowledge fragmentary and naive.

## Notes:

It would take 12.7 million such photos to cover our night sky, and there are 10,000 galaxies in this image.

Folksonomies: wonder astronomy cosmos nasa scale hubble galaxies