Category Archives: Observing

About The Perseid Meteor Shower (“Perseids” For Short)

Greetings fellow astrophiles!

This article has been posted in preparation for our Perseid Session and International Starry Night event at Baltimore Woods this coming Monday, August 12th (with the 13th as the weather-alternate). We might even get a view or two of the Perseids at our Thursday, August 8th Beaver Lake Nature Center lecture!

The Perseid Meteor Shower is an almost perfect combination of location and timing for amateur astronomers and the general public, as the Earth grazes a rich debris field from the tail of Comet Swift-Tuttle during the peak of the Northern Summer. We’ll cover the details of this confluence below so you know what makes the Perseids the most anticipated (and observed) meteor shower of the year.

One Thousand And Thirty Words (And Two Numbers)

Comedian: “Ask me what the key to comedy is.”
Assistant: “What’s the -”
Comedian: “Timing!”

2013august3_swift_tuttle_orbit_v2

The image above shows all of the important pieces of the Perseid puzzle. We find the Earth in its orbit around the Sun as it approaches a mid-August position (the 10th to the 14th, although one may see meteors at the fringe of Perseid territory several nights before and after) that finds Earth (and us) scraping against the edge of a debris field produced by Comet Swift-Tuttle on its 133-year orbit around the Sun. Last seen in our vicinity in 1995, observers will have to wait until the 2120’s for another good view of its flaring core. Fortunately, it leaves enough tiny pieces of itself as it draws close to the Sun to provide us with a brilliant reminder of its existence every mid-August.

Unlike Halley’s Comet, which passes close to Earth’s orbit on its way toward (producing the Eta Aquariid Meteor Shower in early May) and away from (producing the Orionid Meteor Shower in late October) the Sun, Comet Swift-Tuttle’s eccentric orbit finds it passing close to Earth only at one point, like a snapshot capturing a hula-hoop (Swift-Tuttle’s orbit) as it touches the belt buckle (Earth) of a gyrating dancer whose waist is Earth’s orbit in circumfrence.

What’s In A Name?

We refer to this meteor shower as the “Perseids” because the meteors associated with Swift-Tuttle appear to streak across the sky from a point (known as a “radiant“) originating in the direction of the mythical constellation Perseus. The shower itself has nothing to do with the stars of the constellation Perseus, only the part of the sky that Perseus occupies on the late nights and early mornings in mid-August. One might even consider Perseus the beneficiary of this shower, as the constellation has taken on a new-found importance to astronomers over the last several millennia as the marker for this shower in the August skies.

It’s All Relative

Anyone caught driving late at night during a snow storm knows the sensation of making the Millenium Falcon’s “jump to lightspeed” as the snowflakes appear to shoot towards, then past or onto, your windshield. To the driver cruising at 65 mph on a highway, the snowflakes appear to have no motion but the one directly towards the windshield. If you were standing on a snowflake, you’d notice the very slow decent to the Earth’s surface, the rapidly oncoming car headlights, then the swift rush across the windshield as the aerodynamics of the windshield combined with the high speed of the car.

2013august3_lightspeed_v2

This same state of “relative observation” occurs during all meteor showers as the Earth revolves around the Sun. The meteors, themselves mostly no larger than grains of sand, are not moving rapidly towards the Earth’s atmosphere. They lie scattered about the path of Comet Swift-Tuttle, a result of the comet heating enough as it approaches the Sun to lose small pieces of its surface. If Swift-Tuttle were a massive gravel delivery truck (to continue the driving analogy), these small grains would be the random pieces of rock that fall to the ground as the truck bumps over uneven pieces of highway.

Clash Of The Tinys

It is the Earth, revolving around the Sun at a dizzying 110,000 km/hour (that’s 30 km/second!), that powers the meteor shower we see on the ground. As the Earth rushes through the debris field of Comet Swift-Tuttle, these tiny grains of comet come into contact with our atmosphere at speeds so great that they ignite the air around them, causing brilliant streaks of light as the tiny grains are incinerated.

The number of meteors one can observe over a Perseid session is determined by (1) your looking at the right place at the right time (no long blinks!) and (2) the density of tiny Swift-Tuttle-ettes in the comet’s orbit as Earth passes through it. There are some meteor showers where one is lucky to see a few per hour. Because the Earth passes through a generally rich part of Swift-Tuttle’s orbit, two or three per minute may not be uncommon for a “usual” Perseid session. Those outside for the 1972 Perseid Meteor Shower were treated to what many believe to be the best meteor shower in recorded history (and those outside for the 1998 Leonid Meteor Shower (a close second by all metrics) know what it’s like to see thousands per hour raining down on dark skies).

Finding Perseus

The Perseids appear to radiate from the constellation Perseus. For your best chance of seeing Perseid meteors, it is not your eyes that should be transfixed on the heart of Perseus. Instead, you should anchor the bottoms of your toes towards Perseus, then find a comfortable piece of ground (or reclining chair) that gives you a clear view of the sky right above you. Perseid meteors will then, with a thick patch of debris field and a bit of patience, appear to blaze across the night sky from your toes (Northeast) past your head (to the Southwest).

2013august3_perseus_finding_v1

Perseus will appear to rise above the Northeast horizon after 9:00 p.m. Directly above the stars of Perseus resides Cassiopeia – a giant and prominent “W” in the night sky that, for many hours after sunset, will appear as a West-facing throne for this ancient Ethiopian queen. Those familiar with the many tricks amateur astronomers use to learn the Night Sky will simply find Polaris, perhaps using the two end stars of the bowl of the Big Dipper and an imaginary line along these stars in the direction of the bowl’s open face to pick out the dim North Star. Polaris does not shine with the brightness one might have imagined for the second most important star in the sky (after our own Sun), but it is in a piece of sky that contains few brighter stars, making it the most obvious member of a very modest piece of northern sky.

If you’re still too new to constellation hunting, the solution is simple! Grab a compass (or a compass app in your smart phone) and find Northeast the new-fashioned way. With luck, the Perseids will race to the Southwest at a rate of a few per minute, increasing in count, then decreasing, from around 10:00 p.m. to 4:00 a.m. local time. With the good fortunes of all the Olympian Gods, we’ll all be treated to many, many more.

Additional Information

The Perseid Meteor Shower

en.wikipedia.org/wiki/Perseids
earthsky.org/astronomy-essentials/everything-you-need-to-know-perseid-meteor-shower
solarsystem.nasa.gov/planets/perseids.cfm

Comet Swift-Tuttle

en.wikipedia.org/wiki/Comet_Swift%E2%80%93Tuttle
ssd.jpl.nasa.gov/sbdb.cgi?sstr=109P

Meteors And Meteor Showers

en.wikipedia.org/wiki/Meteor_shower
leonid.arc.nasa.gov/meteor.html

Bob Piekiel’s August 12th Baltimore Woods Perseid Session Now Listed As An “International Starry Night” Event

UPDATE: 28 July 2013 – The International Starry Night page for the Baltimore Woods event can be found @ THIS LINK.

Check cnyo.org on the 12th (and 13th) for final event details.
To Register By Email: info@baltimorewoods.org
To Register By Phone: (315) 673-1350
Please register for this event! Low registration may cause programs to be canceled.
Date: Monday, August 12th (weather-alternate: Tuesday, August 13th)
Cost: $5 for Baltimore Woods members/$15 for BW families; $8 for non-members/$25 for families
Time: 9:00 p.m. to 11:00 p.m. (maybe beyond?)
Bring: Chairs (or something to lay on), bug spray, and long sleeves
About The Perseids: See THIS EXCELLENT SUMMARY at earthsky.org
Location: Baltimore Woods Nature Center in Marcellus, NY (directions)


View Larger Map


Greetings fellow astrophiles!

Bob Piekiel, Baltimore Woods, and CNYO are pleased to be hosting a local session for the “International Starry Night,” (herein referred to as “ISN”) an event organized by the “One Star at a Time” Program. While the official ISN night is scheduled for Saturday, August 10th, ISN-related events are being scheduled throughout the days around the Perseid Meteor Shower, and we have opted to host this event during the peak nights of the Perseids. Dedicated amateur astronomers cannot be bothered with such trivialities as their mental states at work on Tuesday (or weather-alternate Wednesday) mornings!

The ISN, which coincides with the Perseid Meteor Shower this year, is being used as a way to organize meteor shower observers and amateur astronomers around to world in the interest of both increasing nighttime observation and decreasing the amount of light pollution through understanding of the issues and public action. As described on the starry-night.org website (and note that their August 10th date is NOT our August 12th date):

2013july20_starrynight_620

Click on the image for a full-sized version (8 MB).

The “One Star at a Time” program is a worldwide effort to create accessible public spaces to view a starry night sky. The program uses night sky conservation to unite people across the planet, their cultures and their skies. This is a story of how people from around the world united together to give the gift of natural starlight for all children of this planet.

A National Parks Service study predicts that unless we can significantly reduce light pollution, by 2025 only 10% of people in the United States will EVER see a starry night sky in their LIFETIME. Similar concerns are coming from all around the world.

“One Star at a Time, Reclaim the starry night sky” is a campaign to engage and unite the public on a global scale to reduce light pollution so that we may reconnect with the stars and each other. The motto of Astronomers Without Borders is “One People*One Sky”. If we can unveil the inspirational night sky we share with all people of this planet, and share experiences and explorations of the cosmos together, we may regain steps toward peace… the greatest gift we could ever give to our children.

On Light Pollution…

Overcast skies and light pollution are THE biggest problems facing amateur astronomy. Unlike the weather conditions, light pollution is a problem that CAN be addressed through legislation and education. International organizations, such as the International Dark-Sky Association, and local groups that lobby for proper lighting legislation, such as SELENE-NY (selene-ny.org), have been pushing for years to educate the public on the potential health risks of light pollution, the importance of dark nights for other species, the best choices of lighting fixtures that help reduce light pollution, and the obvious cost benefits that come from lighting ONLY places that need lighting with ONLY the amount of lighting that is required.

Observers throughout CNY have noticed the increase in light pollution from many familiar observing locations – including Darling Hill Observatory, Beaver Lake Nature Center, and Baltimore Woods. The problem is one of engagement – if more people, organizations, municipalities, and companies know how to illuminate the night in keeping with pro-dark sky practices, light pollution could be greatly reduced. Imagine how much more observing could be done if the sky near our horizons were that much darker!

On the Perseid Meteor Shower…

The issue of light pollution aside, the Perseids and the Leonids often tie for the best meteor showers of the year, with the Perseids benefiting from their appearance in the mid-Summer nighttime sky. The International Starry Night event will find groups around the planet observing the Perseids together (provided the nighttime sky remains clear). And, as an added bonus, the Perseids coincide with the tail end of the Delta Aquarids, a much smaller meteor shower that is more prominent at Southern Latitudes. But we will take any additional shooting stars we can!

But wait, there’s more! The Perseids peak during a Waxing Crescent Moon, meaning the Moon will have set before or near 10:00 p.m. for all five reasonable observing nights (August 10th – 14th). Attendees will have Saturn and the Moon to observe in early-evening skies, then intrepid observers will have Neptune, Uranus, and a host of deep-sky objects to find and observe for the rest of the night.

On the Entire Perseid Meteor Shower Weekend…

The week around the August 12th peak is a busy one for CNYO members. CNYO will also be hosting a lecture and observing session on August 8th (on the 15th as a weather-alternate) at Beaver Lake Nature Center. Maybe a few decent shooting stars on the 8th will hint at a busy Perseid peak on the 10th-12th. We will keep you posted!

CNYO Feature: Going Big

Thinking of going big? Of course you are, and right you should be. Nothing makes up for aperture under dark skies if it’s deep sky objects you’re after. Some may make an argument that refractors show slightly sharper planetary images, but simple physics says the more light you gather (aka, the bigger the mirror), the brighter the image will be. So, how bright and how big is big enough? Let’s take a look at some practical considerations.

Questions to consider before making a final decision on scope size include: What do I most enjoy viewing? Do I observe more at, or away from, my home? How much weight can I comfortably lift? What eyepieces do I currently use? Can I locate deep sky objects by reading a map, or do I depend on computers to point me where I need to go? And finally, do I mind having lines of people waiting to look through my scope, or would I rather observe alone?

The Basics

If you’re a deep sky aficionado, then a big scope will reveal more detail on the faint fuzzies, period. A scope’s light gathering capability is determined by the size of its primary mirror in the case of reflecting telescopes, or its primary lens in the case of refracting telescopes. And you don’t have to double in size to double in light gathering capability. Remember, the area of a circle is π (pi) multiplied by the square of its radius (πr2). With that in mind, here’s a quick reference table of increased light gathering with a number of mirror sizes, each compared to a 4″ telescope:

Mirror Size
Increase in light gathering over a 4″ mirror
Limiting Magnitude*
8″
4x
14.7
10″
6x
15.2
12″
9x
15.6
16″
16x
16.3
20″
25x
16.7
24″
36x
17.1

*Limiting Magnitude – This estimate is based on good seeing, magnitude 6 skies, a 6mm dilated pupil, and 40x per inch of aperture. 40x per inch of aperture requires a well-figured primary mirror. For more information on limiting magnitude, see www.cruxis.com/scope/limitingmagnitude.htm

So, What Does That Mean At The Eyepiece?

The first step is to understand the above table, yet that alone doesn’t tell the whole story. Low contrast objects require not only dark skies and decent transparency, but also aperture. Think about M51, the Whirlpool Galaxy. Under dark skies and pristine conditions, an 8″ telescope will reveal a hint of the spiral arms with averted vision and high scrutiny. Through a 12″ under the same conditions, the arms are easy with direct vision. Through a 16″, knots in the arms can be made out. Through a 20″, the knots are much brighter and M51 begins to look like a black and white photo. Through a 24″, it’s possible to begin to make out faint coloring in the spiral arms, and the core of the galaxy is so bright, one wonders if it’s going to ruin their night vision!

Nebulae, globular clusters and any of the 109 Messier objects are perfect targets for large telescopes. I have found that a 12″ delivers color on the brightest of nebulae, and the color gets easier to see and more vibrant as the telescope size goes up. On globular clusters, an 8″ will resolve M13 and M3, while a 12″ will resolve most of the rest of the Messiers. With a 16″, all of the Messier globs are easily resolved, as well as many of the NGC’s. With a 20+”, you start loosing count of resolved globs!

Planets

Who can resist a peak at Saturn or Jupiter? Well, once again, aperture rules.

As a rule, as the primary mirror increases in size, the ability to discern detail increases. To fully recognize the potential of the large scope, a finely figured primary mirror is necessary. A great amount of discussion has occurred regarding smaller refractors and their reputation to outperform larger Newtonians. This mustn’t always be the case, however, and it would be a serious error to believe the superior view through a refractor is constant, impervious to variables in design, optics and weather. Those in the pro-refractor camp often claim their allegiance is due to the inherent design inferiority of a Newtonian. Nothing could be further from the truth.

A large mirror, such as is found in some Newtonians, must not only be properly supported from underneath, but also on its edge as it is being tilted within the telescope. Many a Newtonian builder neglects to provide the appropriate support. A consequence of an improperly designed mirror cell or edge support system will be any of several detail and contrast robbing aberrations, most notably different orders of spherical aberration and astigmatism.

An important aspect of large aperture Dobsonians (Dobs) is that the larger primary mirror requires far more time to cool down than a smaller refractor. Most of the older large Newtonians out there compound this because it was once thought that the mirror had to be relatively thick, otherwise aberrations would be introduced by the mirror cell (we now have finite computer analysis programs that will plot a perfect mirror cell of any size – most specifically David Lewis’ PLOP program). Thanks to the research of Bryan Greer (research article published in the May and June issue of Sky and Telescope) and others, we now have a better understanding of the ways larger optics shed heat. One of the more straightforward discoveries of this research was that the reason larger mirrors take so long to cool is mostly due to their thickness and not overall diameter. So if we choose the thinner mirror for faster cool down, we again shift our attention to the mirror cell. A thin mirror that is not supported properly from underneath will cause a slight deformation in the surface figure, which in turn causes light rays reflecting off the mirror’s surface to not come into focus at a single point. A star test would then readily reveal different orders of spherical aberration, degrading the view at the eyepiece. Now consider the mirror’s edge support. A sling is historically used to support the edge of large primary mirrors, often made out of Kevlar or metal banding. Through the work of Nils Olif Carlin (www.cruxis.com), we now understand that as much care should be given to choosing the proper edge support as goes into the design of the rest of the mirror cell. If this part of the mirror cell is neglected, you once again will experience different optical aberrations at the eyepiece as the telescope is moved from horizon to zenith.

Another point to consider is that bad atmospheric seeing can cause one to believe that a large telescope is performing poorly on the planets. It is true that a larger mirror will seemingly amplify poor seeing conditions, but patience at the eyepiece (waiting for the seeing to settle momentarily and for the planetary image to “pop”) will once again prove the larger mirror to outperform the smaller one.

So, let us review: A big telescope with a thin mirror, excellent mirror cell and edge support, built with an active cooling system (fans to provide air motion within the mirror box) and a night of good seeing – Viola! It’s a recipe for a night of planetary viewing that will leave you and other observers arguing about the spokes in Saturn’s rings!

Portability

I often hear of an amateur astronomer selling his scope because it’s just too much of a hassle to get out and observe with. The size and weight limit varies from astronomer to astronomer, so observers must carefully consider for themselves what may be too heavy or too much hassle to result in pleasurable observing.

An 8″ is usually considered the “biggest of the small”, while a 12″ is often referred to as the “smallest of the big.” I agree with this sentiment. An 8″ – 12″ tube-style Dobsonian is a one-person job and both easily fit in a mid-sized sedan, but the 12″ may push the weight limits of some. The 8″ scopes on the market today are around 65 lbs fully assembled, while the 12″ telescopes weigh in around 100 lbs. If you plan to use an equatorial mount, make sure to factor in an additional 30 lbs or so above the overall weight (and prepare to spend an extra 20 minutes or so setting up). Forget about 14″ – 20″ tube-style telescopes – portability is key and unless you have a small observatory, an equatorial mount is probably not feasible due to the sheer size and weight it encompasses.

Truss-style telescope weights vary significantly from vendor to vendor. One telescope I can be sure of knowing the weights of is one that I build, a New Moon Telescope. A fully assembled 16″ NMT is just under 100 lbs, the heaviest component you would lift weighing in at 60 lbs, and the collapsed scope readily fits in the same mid-sized sedan that would cart a smaller tube-style scope around. A 20″ is 134 lbs, the heaviest component weighing slightly over 80 lbs, and this is the size at which to start relying on detachable wheelbarrow handles to maneuver it. A 24″ would weigh roughly 165 lbs and a 27″ almost 200 lbs. When going this big, remember to reflect on what type of SUV, truck, or trailer you might like to own, because car-hauling is doubtful. Any of the scopes through a 20″ can be stored in a bedroom or living area (and the 8″ and 12″ even in a closet), fully assembled, should you choose to showcase them as pieces of furniture. From the 20″ and up, consider utilizing a storage shed, garage, or an observatory (should you be so fortunate!). Keep in mind, telescopes 20″ and larger necessitate a large car in which to travel, or ideally a truck, trailer or SUV, so if you’re an apartment dweller with no access to a storage unit, you’ll want to stick on the small side. Likewise, if you have your own observatory in your backyard, the sky is the limit on the size of scope you could choose, as portability will not be a factor.

Eyepiece Preference

One factor that may be overlooked when considering the purchase of a new telescope is the choice of eyepieces. The longer the overall focal length of the scope, the smaller the field of view (and so the higher the magnification), so the limited field of view of Plossl eyepieces quickly become frustrating when you start using telescopes in the 20″ range. Another factor about your eyepiece collection is the capability of the eyepiece for correcting coma. Coma is an aberration you get with any Newtonian, in which the stars in the eyepiece start looking like tadpoles as they near the edge of the field of view. Everyone seems to have a different tolerance level of coma, but there are ways to correct for it. The easiest – buy all high-end eyepieces. TeleVue, Pentax, Explore Scientific, and a few others are building eyepieces that contain coma-correcting elements (and of course FAR wider fields of view than the typical Plossl) and these usually perform well down to a focal ratio of F4.5. Faster than F4.5, you may need to invest in a specific coma-correcting eyepiece such as TeleVue’s Paracorr (I cannot recommend these enough). All of this being said, you could observe happily for the rest of your life with three high end eyepieces and a barlow lens with as large a telescope as you wish to endeavor (my opinion only of course!).

Further Considerations

Familiarity with the skies will also likely determine the size of the scope to purchase (or build, of course). The obvious determining factor here is cost. If you are brand new to astronomy and can’t tell the difference between Cygnus and Sagittarius, you should probably wait to invest in a $15,000.00 set-up, even if you can afford it now. A modest familiarity of the sky is needed when using any telescope, and wisdom has shown that beginners typically have an easier time with a simple pair of binoculars or a small telescope. In fact, many of the 8″ tube-style telescopes on the market right now are under $400, and perfect for a beginner. Purchasing a telescope like this will give you the time under the stars you need to learn the constellations and familiarize yourself with pointing, moving and using a telescope. If you are a more advanced amateur, however, bigger scopes and better optics start to make more sense. You have probably amassed a few decent eyepieces and know your way around the sky well enough to invest in a larger scope that will open the skies to you exponentially. Even if you aren’t a star hopping pro yet, there are digital encoders available and GOTO capabilities that can be added to even the largest of telescopes. Think of it this way: with a good NGC and IC map (or encoders), you could go to a dark site every night for the next 20 years and upon each visit discover a new deep sky object! And with some of the more obscure objects, you may be one of only a handful of people that have EVER seen said object through a telescope! And remember – the bigger the mirror, the brighter and more picturesque the object is going to look. And of course there’s always that chance of discovering a comet…

Finally, big scopes draw crowds, and crowds are the future of amateur astronomy. If you can point at a few nebulae, open clusters, or galaxies and give a 60 second presentation on what you are looking at, you will quite possibly change the lives and perspectives of countless people. So that’s my final “big scope” pitch: Big scopes change lives!

2013june25_ryangoodson_bioRyan Goodson is the owner of New Moon Telescopes (www.newmoontelescopes.com), manufacturer of custom Dobsonian telescopes. He is a member of several CNY astronomy clubs, hosts observing sessions from his dark skies in West Monroe, NY, and lectures regionally on telescope building. He can be reached at ryan@newmoontelescopes.com.