Site logo,

A question of distance

Q: If you have a camera, what is the greatest distance from which you have photographed anything?

A: You might say 30km (20 miles) or so, that being the distance of the horizon in a landscape.

Think again. Have you ever included the moon in any of your shots? If so you have to multiply your answer by more than 10,000. The moon is 384,000 km (240,000 miles) away.

The moon through 300mm lens at 1-to-1 pixel size

Canon EOS5D 100-400mm lens at 285mm 1/1000s
f/5.6 ISO400 2008:2:11 17:52:05

Have you photographed the sun at sunrise or sunset, or inadvertently included it in a daylight shot? If so, multiply by another 400. The sun is so far away that its light takes 8.3 minutes to reach us. So we can say the sun is just over 8 light-minutes away.

Have you tried putting your camera on the ground facing upwards at night and taking a long exposure to see star trails? you don't need a fancy camera to do that. (More on that idea is described here.) Most of the brightest stars are around 10 to 100 light years away - their light takes 10 - 100 years to reach us. That's 6 hundred thousand to 6 million times further away than the sun.

Still using nothing more than a cheap camera, though it would help to put it on a simple tripod, if you aim it in a certain direction in the constellation of Andromeda you can photograph the nearest galaxy outside our Milky Way. The Andromeda Galaxy (known to astronomers as M31) is about 2 million light years away. It is just visible to the naked eye as a faint patch of light provided you know where to look and your local street lights are not too bright. It is the furthest object that can be seen without optical aid.

Cameras, even cheap ones, can do better than the naked eye by taking long exposures. The main difficulty then is the rotation of the earth, causing objects in the sky to trail and blur. On these pages you can see how software such as GRIP can overcome that problem. (Start at the same reference as the previous one: here.)

Adding more equipment helps of course. A motorised tripod, compensating for the earth's rotation, is the first thing to get. Mount the camera on it directly, as shown here. Then of course a telescope. And in due course a bigger telescope. With my 254mm Newtonian I have photographed a group of galaxies called Stephan's quintet. Alright, it is only a faint blur. The staggering thing is that most of that blur is caused by light emitted 300 million years ago! And yet I can catch it in my camera in my own back garden. (More recently I have gone considerably further, to 5 billion (5 x 109) light years: see 3C66A.)

But you really don't need either a motorised tripod or a telescope to see some amazing things. Have you photographed the craters and mountains on the moon? You probably can, especially if your camera is recent and therefore has at least 6 megapixels. The moon photo above was taken without tripod or telescope. I have a page that explains why first results usually seem disappointing but that you only have to enlarge the picture to do better than Galileo could.

Galileo was the first to see the 4 principal moons orbiting Jupiter. Today it is possible to photograph them without a telescope and here is an example.

Jupiter photographed without a telescope

Canon EOS D60 70-300mm lens at 300mm 23 x 10s
f/5.6 ISO800 2003:3:22 20:05 - 20:38

In this case the camera was riding piggy-back on a Meade ETX-125 telescope, as shown here. Jupiter is grossly over-exposed, as it had to be to photograph the fainter stars and satellites around it. The over-exposure caused diffraction spikes from the multiple blade edges of the iris diaphragm in the lens.

There appear to be four stars close to Jupiter. In fact two are stars and two are satellites. Of the four bright satellites of Jupiter two (Io and Europa) were either in front of or behind the planet at the time the photo was taken. From the left we can see Callisto, a magnitude 8.3 star, Jupiter, Ganymede, and a magnitude 9.5 star (not so well aligned as the others). Jupiter had recently passed in front of M44, the Beehive Cluster, which is the spread of stars above and to the right of the planet.

The 4 main satellites of Jupiter are like a mini-solar system that can be seen to change hour by hour. It can be fascinating to watch that happening. With a small telescope it is possible to see their shadows crossing the planet and them being eclipsed by the planet. At certain times in Jupiter's 12-year orbit around the sun (and it is true now, early in 2010) the satellites can occult (hide) and eclipse each other.

Next page