Star Parties, Lawnchair Style - Tips for a Memorable Stargazing Party
A Lawnchair for All Seasons
The Magnitude System
Red & Blue Shifting
What could be better than sharing a lingering look into the universe with dear friends and family under a really dark, star filled sky? If you plan it correctly, you'll create memories that will last a lifetime. Here are some things to consider in order to create a spectacular night out under the stars.
The thrill of getting out of the house and staying up all night is just the first part of the most memorable evening you, your kids, neighbors and friends can have during the summer. You might start by developing the guest list, cleaning up the backyard, polishing the Lawnchairs and making sure the BBQ has plenty of propane, or charcoal, for the purists like myself.
The weather, of course, is always a major concern. Clouds and rain are the mortal enemies of the Lawnchair. While skies may remain clear all day, an approaching front can only serve to ruin your plans. It’s best to keep an eye on the weather sites and track what's in store for your area. Summer often tends to see an increase in humidity. Because of this, early evening skies can often be a bit hazy. Fortunately, as the night wears on, this moisture dissipates and typically, by late evening and early morning, skies are primed for observational inspection.
The next consideration is location. If you live in the city, then your backyard perhaps isn't the best place to consider a night out under nature's tapestry. Ideally, if you can get away from the city, perhaps as little as twenty miles or so, then you should be able to find a nice dark place to setup your Lawnchairs. What constitutes a nice place depends on what exactly you want to see. Of course, if you’re looking to capture some deep sky targets via telescope, then the darker the locale the better. You want to stay away from places where there are street lights, billboards and the worst light pollution offenders, auto dealerships, shopping centers and malls. Even in rural communities these days, light pollution is, more often than not, becoming an issue and serving to limit the ability for both amateurs and professionals alike to enjoy dark, clear skies. The best advice I can offer is to get as far away from any city or town as possible.
Once you find your way to a dark sky, what else should you look for in an observing site? For starters you want to be able to see as large a piece of sky as possible. A large open field is ideal, especially if it is on a hill providing panoramic access to each horizon. However, there is also the concern that the horizon in the direction of nearby cities will be awash in a glow of light. So you have your choice of either setting up in a valley field limiting your access to some of the low horizon targets or, a hill where you may be inundated with extraneous light from far off cities and towns. So depending on how close you are to a light source, your decision will affect how much sky you will have to see. But lastly, don’t worry about seeing right down to the horizon as this is not the best area to observe objects in. Looking through the atmosphere at a target low to the horizon is often distorted by varying temperature gradients along the line of sight, interrupting a steady light path. Similar to a looking down a long road on a hot summer day and seeing those view warping mirages.
Next on the list of parameters for a great stargazing evening is the question of when is best to attempt such a feat. Well, as it is with city lighting, the moon, too, can serve to lessen the success of a wonderful night out. Cyclic, there are both good and bad times to observe. For instance, when the moon is rising full in the east it will persist all evening and make finding and observing any deep sky objects much more difficult. However, when you see that sliver moon in the early evening heading down toward the western horizon, rest assured that the remainder of the night will provide crisp dark skies in which to peruse at will. And this is also the stage in the moon's cycle when it is best to observe it. When the Moon is full, it’s simply too bright to do any meaningful observing.
Throughout the first and last quarter stages of the lunar cycle the light levels, though still bright, are easily managed and viewing the moon is much easier and typically more rewarding. Viewing along the terminator or the line of day/night separation on the moon can provide some interesting sights through a pair of binoculars or a small telescope. Look for sun rays peeking through the mountaintops, illuminating portions of the moon ensconced in nighttime. The moon is often a great starting point for an evening of observing.
Then there are the planets. Known as wanderers since antiquity, you'll need access to either computer generated planetary information, the web, or hard copy published tables regularly found in many newspapers and magazines. Seeing Saturn in person is always a wonderful surprise. Jupiter and Mars are also excellent sights to behold in the eyepiece. Mercury, being so close to the sun can be challenging to see as it typically rides very close to the horizon and, time for viewing is limited before the sun rises or sets. Venus, though, spends more time above the horizon. However, covered in clouds, it is generally featureless, other than the fact that it, too, like the moon, experiences phases. Sometimes it can be seen in full, at others, just the waning or waxing phases.
The remaining, Neptune and Uranus, are difficult to capture in backyard grade instruments. The best opportunities to see these two elusive gas giants are when they reach opposition to Earth (closest point) and oftentimes can be found near an easily located star. They are not generally much to look at if you do indeed locate them. Both present as small dot like images. In the case of Neptune, its blue shade is the dead giveaway.
When, is a subjective concept, especially when discussing the opportunities to take a well ensconced Lawnchair out into the realm of rewarding astronomical pursuits. Targets abound in a dark sky and many are available to peruse at any time of the year. For example, the circumpolar constellations never really set as they play hobby-horse to Polaris, the North Star. The entire sky rotates around this point in the heavens. Most of these constellations can be seen year-round: Ursa Major and Ursa Minor, the Big and Little Dippers are examples.
Those constellations further away from this central point, however, are occasionally overtaken by our parent star and, for a few months each year, are said to be traveling with the sun. It’s like when the moon is at its waxing and waning extremes each month, when for a few days it is absent from both evening and early morning skies until it reemerges from the sun's glare, at the beginning of its "new" phase.
This is also true of the constellations as well. In early November, for example, some of summer's finest sights are available to see in the late afternoons after the sun sets, not yet having reached that point where they disappear with the sun below the horizon. But then, some of those glorious sights like those you’d see in Sagittarius, which you’d normally endeavor to capture on a warm July evening, can be glimpsed during an early morning jaunt out into a frozen, yet crisp mid-February morning sky before the sun rises.
So take that to heart as you read through the following monthly chapters. There is more than one way to skin a cat and, there are certainly many ways to satiate a thirsty Lawnchair's observational desires. Many of the constellations described in the following sections can be seen, whether in the early evenings, late nights or pre-sunrise mornings for up to nine months or longer each year.
Stars are classified in a variety of ways: size, spectral class, motion, age and, most relevant for Lawnchair astronomers - brightness. These measurements are referred to as a star's magnitude, at least as to how bright they appear to us. They are, of course, also classified by their "absolute magnitude" which is how bright they would appear from a distance of ten parsecs (a parsec is equivalent to 3.26 light years).
The earliest reference to this system of cataloging stars came from the early Greek astronomer Hipparchus in 129 B.C. About 270 years later Ptolemy incorporated and refined this system for use in his own star catalog. The basic concept is that the brightest stars are rated as first magnitude or Magnitude 1 stars. The dimmest stars that could be seen with eyes alone were cataloged as Magnitude 6 stars. Those on the scale in between are, of course, 2 through 5.
However, once the telescope was added to the equation, astronomers realized that there was more than meets the eye with regard to stars. Starting in Galileo's day, it became apparent that there were many more stars there than what could be seen with eyes alone. The categories were expanded to include stars dimmer than Magnitude 6. Backyard telescopes of size can "see" stars as dim as 15th and 16th magnitude, while the Hubble Space Telescope has recorded stars as dim as 31st magnitude.
The scale is also expanded in the other direction using negative integers such as Magnitude -1 and -2, etc. The bright planets Venus and Jupiter, for instance, rate as -4 and -2 magnitudes respectively, while the brightest star Sirius comes in at magnitude -1. The sun on this scale is Magnitude -26, while the moon rates a Magnitude -13.
Under very dark skies, our eyes can detect stars as dim as Magnitude 6. That said, without the aid of binoculars or a telescope, we can see approximately 3000 stars under ideal conditions. As we know, however, that's not even the tip of the iceberg. It is estimated that there are three hundred billion stars in our galaxy alone, give or take a hundred billion or so. A step further would include an almost infinitely inconceivable number, given the estimates of how many galaxies there may be within the universe, today thought to be perhaps as many as five hundred billion. The Lawnchair has occasionally, though not so eloquently uttered, "That's a sh"#load of stars"!
At the distances of galaxies outside ours, a simple parallax-based measurement doesn’t work. After a certain limit, parallax measuring methods break down, specifically for objects as incredibly far away as other galaxies. It works fine in our local neighborhood. In analyzing the light from very distant objects, one of the more interesting aspects of these signatures is that they are "shifted" to either the blue or red end of the spectrum, depending on the direction they’re traveling. Approaching objects generate a blue shifting of their spectrum, while receding objects display a red shifting. Additionally, the more red or blue shifted an object's spectra is, the faster it is moving.
Call it an old astronomer's trick, but it does work. The center of our eyes having been bombarded with light since birth become less and less sensitive to light as we age. While some of us are older than others, beards greying and bones regularly beginning to creek, seeing in general slowly deteriorates.
The trick: look slightly away from a dim object, to the immediate left or right. This lets the more sensitive sides of your eye detect what you'd not be able to see looking straight on.
The result is that very dim objects can be glimpsed, albeit only fleetingly, as you move your gaze off the target. However, as soon as your eye naturally returns to the object, poof, it will seem to disappear.
To try this techniques yourself, look for the three stars that make up Orion's Belt. From there, look down below the belt and notice what looks like three stars, (the scabbard) much closer together than the belt stars and at an obvious angle to the belt. This is where the Great Nebula resides. Of these three stars, the middle one, is the Nebula. Now, sometimes, when looking right at it, this middle star will seem to disappear. Then, amazingly, as you look away from it slightly, poof, it pops back into view, only to disappear again as your gaze returns to it. This is how averted vision works. It’s one of a handful of tricks that you'll become accustom to when searching the night skies for these wonderful, though often times dim jewels of the heavens.
The Lawnchair Astronomer
Gerry Descoteaux is the author of “The Lawnchair Astronomer,” a Dell Trades paperback. He has been writing about astronomy for more than 25 years. He also played an integral role in the development of America Online’s pioneering distance education program known as AOL’s Online Campus and served as Professor of Astronomy there for 10 years. He can be reached at TheStarMan@thelawnchairastronomer.com.
Notes From the Lawnchair