# How long does it take for pictures by Hubble to arrive on Earth?

Recently, there was news that Hubble took a high definition picture of the Andromeda galaxy. I wanted to know how long does a high definition picture from Hubble takes to arrive on Earth; if at all possible, how does this process occur?

• Are you asking about the time it takes to transmit (by radio waves) the signal from Hubble to Earth? Or the time it took the light from Andromeda to reach Hubble? – Floris Jan 13 '15 at 1:20
• Or, possibly, Hubble's downlink bandwidth in kilobytes/second and typical image data sizes in kilobytes? – rob Jan 13 '15 at 1:26

Hubble transmits about 120 GB of data per week (source: http://hubblesite.org/the_telescope/hubble_essentials/quick_facts.php). One picture of the original camera was only 640k pixels (this camera was built a long time ago), but the images you see are composited from many many images. Today, it uses WFC3 - a 8 mega pixel camera. Even so, a single image from the Hubble takes very little time to transmit - but depending on which composite image (dataset) you are talking about, the answer could be "a very long time".

The time for the radio signal to travel back to earth depends on the distance to the transmitter, but since its orbit is only 569 km above the earth's surface, it could be as little as 2 ms. From the furthest point it will be about 4000 km away, so it would take 13 ms for the signal to reach earth (speed of light ~300,000 km/s). Note that the article linked below says that Hubble doesn't in fact send data to Earth - instead it sends it to the geosynchronous tracking and data relay satellite system (TDRSS) twice a day, which will add some delays.

A more detailed answer is at http://en.wikipedia.org/wiki/Hubble_Space_Telescope#Transmission_to_Earth

And I just found this cool picture (source):

As for the size of the Andromeda data (the Panchromatic Hubble Andromeda Treasury), you can start at https://archive.stsci.edu/prepds/phat/ and dig down to the data files from there - for example, when you drill down to brick 1, you will come to https://archive.stsci.edu/pub/hlsp/phat/brick01/ and you'll see a long, long list of files that amounts to about 94 GB of data. And that's just for one brick. There are 23 bricks. But note that these are not raw image files as sent by Hubble. It seems reasonable to think it took a few months though.

• cool, but what about that high definition picture? How long would that take? Meaning, how many pictures there are on that times the transference time – rafb3 Jan 13 '15 at 1:31
• "That" high definition picture? Do you have the dimensions? Note also that the pictures would most likely be overlapping, and that a lot of the imaging is done sequentially - many different filters are used to create a composite (color) image from a series of monochrome images. So depending on how many colors (wavelength bands) were acquired, the answer will change. – Floris Jan 13 '15 at 1:35
• There's probably more effort in reshaping the dozens of images to blend them into a beautiful composite image (especially when using more than just Hubble) than there is effort in getting pictures to Earth. – Kyle Kanos Jan 13 '15 at 1:45
• @Floris yeah, that picture from the Andromeda galaxy. I believe you are right and there is all that to consider, but what would the result be? Or at least how can we have a rough estimate? – rafb3 Jan 13 '15 at 1:48
• @KyleKanos ok, but that's not the point. – rafb3 Jan 13 '15 at 1:48