We have all enjoyed the images from the Hubble telescope. What sets those pictures apart from those taken with Earth-based telescopes is the unprecedented detail, or the Hubble’s resolution. Resolution is the ability to tell two things apart that are very close together.
You can measure angular resolution by simply finding the angle between your eye (or camera, or telescope) and two different objects, such as two different stars. If two stars are so close together that they look like one star, we say they cannot be resolved.
Rather than saying how well your vision is with a quantity like “20/20 eyesight,” your optometrist could give the smallest angle you could resolve. People with 20/20 vision can typically resolve things that are about one arc-minute (one-sixtieth of a degree) apart.
To get a feel for how big one arc-minute is, hold your pinky finger out at arm’s length. At that distance, your fingernail is about one degree wide and about one arc-minute thick.
If you use a telescope, your resolution can increase dramatically. For example, the Hubble telescope’s resolution is 0.05 arc-seconds. There are 60 arc-seconds in one arc-minute, so the Hubble’s resolution is about 1,200 times better than an average human eye.
Unfortunately, Earth’s atmosphere limits the resolution of traditional terrestrial telescopes to approximately one arc-second. If we didn’t have to look through the atmosphere, all telescopes, lenses and eyes would have a resolution limited by their diameter. This is the physical result of light being a wave that will bend as it encounters an edge or an aperture of a telescope. Double the diameter and your resolution gets twice as good.
Digital photography introduced a common misconception concerning resolution. Early digital cameras were limited not by the camera’s optics but mostly by the number of pixels in the sensor. Getting better sensors greatly improved the resolution of those cameras. Today, most sensors have overcome this limitation, so we are back to the physical limits of the optics. In most cases, increasing your pixel count will not increase your resolution, but getting a lens with a larger diameter will.
This monthThe summer solstice, which is the official kickoff to summer, is June 20. Also on June 20 is this month’s full moon. On July 4, you will be able to not only celebrate the nation’s birthday but also Earth’s aphelion. That is the day the Earth is farthest from the sun.
Jupiter, Mars and Saturn are well positioned for evening viewing right now. Jupiter will be at its highest just after dark, and the orientation is good for catching eclipses and transits of the Galilean moons. Mars and Saturn, following Jupiter by a few hours, will be at their highest points just before midnight.
There are two new ways to connect with the Four Corners Stargazers group. A Google website and a Facebook page have been set up to keep stargazers in touch with each other. See the “Useful Links” box with this column.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Email him at firstname.lastname@example.org.