By Ernie Jacobs, Astronomer
One of the goto targets for summertime stargazing is M57, the Ring Nebula. Located in the constellation Vega, it’s relatively easy to find and is visible in most equipment used by amateur astronomers. The Ring Nebula has been featured prominently in promotional material for our upcoming (July 29th) Astronomy Night at Penn Dixie. So what is it? What’s with the “M57” thing? Where is it? What can be expected when looking through the eyepiece?
Deep Space Objects
The Ring Nebula is what astronomers refer to as a Deep Space Object or DSO. Basically a DSO is any object beyond our solar system (something other than the Sun, Moon or the Planets). Galaxies, Nebula, and Star Clusters are all examples of various types of DSOs. The Ring Nebula belongs to a type of DSOs known as Planetary Nebulae. There are a few types of Nebulae: Reflection, Emission, and Planetary. Planetary Nebulae are the remnants of stars similar in size to our Sun. Stars up to about eight times the mass of our Sun are too small to explode in a Supernova at the end of their lives. Once the stars can no longer fuse Hydrogen or Helium, the star sheds it’s outer layers of gas.
A hot dense ember known as a White Dwarf is all that remains of the star and the expelled outer layers are ionized by the this White Dwarf remnant, creating the object that we view. So why are they called Planetary Nebulae? Do they have anything to do with planets? When they were originally discovered, astronomers had no idea of their true nature. In the telescopes of the time (eighteenth, nineteenth centuries) they appeared very similar to planets. One Planetary Nebulae looks so much like Saturn (NGC 7009) it’s called the Saturn Nebula.
So now we know what the Ring Nebula is and what the “Nebula” part means in the name. What’s the deal with the “M57” thing? Well the Ring Nebula is contained in a Catalog (a list) of objects created by Charles Messier. The “M” refers to Messier and it’s number 57 on the list. Charles Messier was a French Astronomer that lived from 1730 to 1817. He was primarily interested in finding comets, indeed he found several, but ironically he is not known for finding comets. Messier started a list of objects which appeared fixed with respect to the stars, moving each night with stars as opposed to moving through them as comets do. He created the list so fellow comet hunters wouldn’t waste anytime observing these objects. The objects are relatively bright and are therefore easily observed by amateurs and are popular targets at Public Astronomy Nights or Star Parties.
In March/April it is possible to view all 110 objects in one night in what is called a Messier Marathon.
In addition to being well suited for the equipment frequently used by amateur astronomers, M57 is relatively easy to find. It’s located near one of the brightest stars in the summer night sky (Vega), within a prominent summer asterism (the Summer Triangle), and right between the two bright stars Sheliak and Sulafat in the constellation Lyra. These factors make finding the Ring Nebula relatively easy.
Time and Distance
So that’s how to find it in the Night Sky, but where is it in relation to Earth? The Ring Nebula is 2,283 light-years from Earth. A light-year is the distance light travels in one year (about 300,000 meters/second or 186,000 miles/second). That is about 5.8 Trillion miles in a year. Space is unimaginably large and requires truly astronomical units of measure. Nothing can exceed this cosmic speed limit. The result of the finite speed of light, is that looking through a telescope is like looking through a time machine. We see these objects not as they are now but how they were. We see the Moon as it was a few seconds ago, the Sun as it was about nine minutes ago, Jupiter as it was about forty five minutes ago, and the Ring Nebula as it was 2,283 years ago. The Ring Nebula, cosmically speaking, is very young at about 7,005 years old.
Our Eyes vs. Telescopes
Finally, it’s time to address the 800 pound gorilla in the room. What will M57 look like when viewed through one of our telescopes? Major spoiler: it will not look like the colorful images like the one used to promote our upcoming event or that can be found in many other forms of media. So what’s going on? Well, to be completely honest, this is one of the greatest challenges the we face with astronomy outreach. With the advent of digital imaging techniques, the Hubble Telescope, & the internet, astronomy has benefited tremendously from the excitement that these amazing images generate. Unfortunately, for some it can be disappointing that what they view through the telescope is not as colorful and detailed as in these images. So what’s going on? Are NASA and astrophotographers tricking us? Is our equipment used for visual observing substandard? The answer to both questions is no. What is needed is an understanding of how both technologies work so that expectations can be properly set.
When observing distant objects through a telescope it is important to understand that it is very difficult to see color in the objects viewed, unless they are very bright. Typically, it is possible to discern colors in the planets (Jupiter, Saturn & Mars for example) and sometimes in the Orion Nebula (M42). In some cases color can be perceived in other objects under favorable viewing conditions (clear and dark sky) with telescopes that have a large aperture. The reason we don’t perceive color when looking through a telescope has to do with the part of the eye we use when observing (cones vs. rods) and our sensitivity/ability to collect light with our eyes. Our eyes are truly amazing, and in no way is this intended diminish their amazing capabilities in any way. The cones are good at detecting color but are not that sensitive. The rods are more sensitive and are therefore able to detect the light. Unfortunately the rods cannot detect colors and have poor resolution.
Additionally, our eyes work much differently than a camera. In some cases this is an advantage. When looking through one of our telescopes at the planet Jupiter, it is common to be able to see Jupiter’s Belts/Bands and the four Galilean moons at the same time. Ours eyes have incredible dynamic range. When imaging Jupiter it is a challenge to capture the details of Jupiter’s clouds and the moons at the same time. In order to see the details on the planet’s disk, the exposure setting must be low. The consequence is that the moons, which are much dimmer than the planet, may no longer be visible with a lower exposure setting. Increasing the exposure to reveal the moons blows out (over-exposes) the planets surface.
However, cameras do provide a distinct advantage over eyes when it comes to capturing images of distant, faint, and diffuse objects. The camera’s shutter can be left open for extended periods, increasing the amount of photons collected on the camera’s chip.
Let’s perform a little thought experiment to help understand what’s going on. Imagine you have a paper plate resting on a flat surface. Now sprinkle something granular on the plate, grains of sand for example. Do this for a second or two. How well will the grains of sand cover the plate? When poring the sand out quickly, there won’t be enough grains of sand to thoroughly cover the plate. There will be many places where there is no grain of sand covering the plate and the grains will be non-uniformly distributed over the plate. The plate represents our eye or the camera sensor. The grains of sand represent the photons of light from a distant object.
Now lets repeat this experiment. This time increase the amount of time that the sand is poured onto the plate, let’s say a minute or two. Now the plate has collected more photons and there are significantly less gaps if any. This is why photographs of astronomical objects can show so much more detail and color. Additionally, there are other techniques of capturing the images and processing that impact the color of the image as well. We won’t get too technical, but the colors in the image may not be what can be seen with our eyes, but the do represent real aspects of the object.
When looking through our telescopes visually (we often have one of our telescopes setup to image during an event) the Ring Nebula will look like a small, faint smoke ring or doughnut, not the spectacular psychedelic image from the Hubble Telescope. However, it’s just as amazing. The light hitting your eyeballs left the Ring Nebula almost 2,300 years ago. What was Penn Dixie like 2,300 years ago — that’s a question for a geologist not an astronomer. What civilizations existed 2,300 years ago? As previously stated, looking through a telescope is like looking back into time. It provides an opportunity to try to comprehend the incomprehensible vastness of the universe and our humble place in it.
Hope you come out Saturday July 29 and we hope the weather cooperates. We’ll have a nice nearly quarter moon to look at, the planets Jupiter and Saturn, and many DSOs like the Ring Nebula to show you. Additionally, I will be joining our Buffalo Astronomical Association (BAA) colleagues at Wlikeson Pointe on Friday July 28th for some observing at the Outer Harbor.