Script For Summer Sky
This file contains the raw script for the movie. Since I have
to talk very fast to make each segment short enough to meet YouTube rules, my
sound track may be hard to follow for those that english is a second language.
This is the actual script used to compose the movie. The numbers correspond
to sound tracks. The text in red and green are markers for what is
happening in the video. You should use
these as a way of marking the boundaries between scenes. Some of the scenes may
differ from the script since I found some more clever ways to do things.
If you look southeast in June from a site that is reasonably dark you will notice a band of light rising from the east. At first this looks like just more light pollution, but as it gets higher in the sky it resolves as a distinct band of light brightest in the south and dimming perceptively towards its north side. This is the glow of our galaxy. Its presence marks the entry of the summer sky and its wonders.
In this section of the video I will discuss what you are
seeing - our Milky Way. This is the galaxy that our sun is a part of. I will
show sections of the Milky Way to you that you cannot see from the
The summer sky provides opportunities to view virtually every type of astronomical object. Many of these are located along the band of Milky Way we will be discussing. I will tell you about them in the later sections. For now let’s talk about the Milky Way.
The brightest portion of the Milky Way visible from the northern hemisphere is here in and around the constellation Sagittarius. To modern eyes this constellation appears to be a teapot.
The naked eye visible Milky Way is the combined light of hundreds of thousands of stars. The Milky Way itself consists of billions of stars.
The image as it appears now is similar to what you will see with your eyes. Our eyes perceive dim light as shades of grey. Color is only perceived if the source is brighter.
Using a camera we can view the colors that are too dim (or too red) for our limited color vision to detect. This makes several features easier to see.
Note the dark area that divides the two light areas. These dark areas are dust clouds. The clouds are small particles (from a few molecules to 0.1mm) that are the detritus left over as stars die.
The small grains diffuse visible light hiding brighter areas of the galaxy. While visible light can not penetrate the dust other portions of the electromagnetic spectrum do. The dust itself also radiates in other portions of the spectra. We will see this later in the video.
Note the reddish areas on either side of the dark band. The red color mostly comes from hydrogen gas. This is the stuff of new solar systems.
The center of our galaxy is located about here. The dust clouds hide the bright center of the Milky Way from viewing, at least in visible light
The Milky Way circles the earth as a nearly continuous band
of light. The portion of Sagittarius shown
here is the brightest section visible in the
Let’s take a tour of the entire Milky Way.
This strip image of the Milky Way in visible light was compiled by Axel Mellinger. The author is grateful for permission to use it in this video.
Since entire Milky Way is never visible at the same time this is required a series of pictures taken from several locations around the world. For more information see Mellinger’s web site which is listed in the credits at the end of this movie.
Let’s get our bearings again. First we will move north to see the other prominent land mark of the northern sky- The summer triangle
Three bright stars dominate the eastern sky in early June. As the summer progresses these will be overhead at twilight. We call these stars the summer triangle.
Vega and the constellation Lyra is
at the top of this photo. Altair and the
constellation
Continuing north from Cygnus we reach Cassiopeia which will
be low in the north during the summer. It will be easier to view this portion
of the Milky Way in the winter from the
Let’s return for the moment to Sagittarius and I will move
into a portion of the sky that is too far south to see from the
Since many of the viewers may not be familiar with what is
below the horizon for us in the
The Alpha Cent system is the closest star system to earth at about 4 light years.
The Southern Cross is a famous constellation of the southern
skies and is on the
This bright area in the constellation Carina contains the nebula associated with the star Eta Carina. This is a supernova in the making.
The large red circle is the Helix Nebula. Only 450 ly away it is one of the closest planetary nebulas
Continuing further we now start moving north again, but to a
portion of the sky hidden by the summer sun. We are now entering the portion of
the Milky Way visible in the winter from the
Sirius is the brightest star in the sky and shines brightly over the winter sky
Most of the constellation Orion lies just below this strip.
As we continue moving further north we move through Perseus and again come to Cassiopeia.
That completes our tour of the Milky Way. Looking at the entire panorama the dust lane and the center bulge are easily seen.
The public is most familiar with photos taken in visual light using the Hubble Telescope. Astronomers also use a variety of other land and space instruments to examine the sky. Each type of radiation tells a story about a particular kind of activity.
Gamma Rays are the shortest wavelength and most energetic. These have even more energy than the X Rays we all experience at our dentist’s office. They are produced by high energy processes like those happening in the center of our galaxy. The bright, compact sources are associated with pulsars. This Gamma Ray image was compiled by the Compton Gamma Ray Satellite.
This shows what the Milky Way looks like at 408 Mhz in radio wavelengths. Most of the emission is from electrons moving through magnetic fields at nearly the speed of light. This happens near supernova. Radio is also a tool used to probe the center of our galaxy.
The infrared image is from the Infrared Astronomical Satellite (IRAS). Most of the emission is heat from interstellar dust warmed by absorbed starlight, including star-forming regions embedded in interstellar clouds.
One product of observing in these various wavelengths is that we can now map the stars orbiting the black hole at the center of the Milky Way. This movie was complied by UCLA using the Keck telescope observing using infrared radiation at 2.2 micron. For more information see the references in the credits or Melia’s book also listed in the credits.
We can tell from the various spectra the Milky Way is a flat disk with a central bulge. From the side our galaxy would look like this picture of NGC 4565.
Determining the shape beyond that requires some detective work and detailed analysis in all of the various bands of radiation as previously shown. In recent years there has been a lot of progress.
Astronomers can tell that the central bulge is not spherical. Instead it is what is called a “barred spiral”. This picture of M109 taken by local astrophotographer Richard Crisp shows a galaxy whose shape is similar to the Milky Way’s.
But what is the shape of the spiral arms? Since we are inside the disk that level of detail is not easy to determine.
The number of major arms in the Milky Way is something that has changed as we learn more. According to the latest research the galaxy has two principle arms; the Perseus Arm which would be in our Winter sky and the Scutum-Centaurus Arm which contributes to what we see in our summer sky.
The sun is in a minor arm called the Orion Spur. Most of the stars we can distinguish with our unaided eyes are also here.
Since we are located in the plane of the arms, it is difficult to tell where one arm begins and another ends in the sky. The work to determine the structure has instead been done by careful measurements. See the credits for more information on how the shape of the galaxy was determined.
I hope this gives you a better appreciation of what the glow in the sky is. In the next section we will talk about some of the more interesting deep space objects of summer and how to find them.
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Welcome to the second section of my video on the summer sky. In the remaining sections of this video I will introduce you to some bright objects in the summer sky. Many of these can be seen with a pair of binoculars. All can be observed using an 8” telescope from a suburban site; however, as I described in my Star Hopping Video Series, going to a darker site would be better.
In this section I will focus on Messier Objects in the constellation Sagittarius. In the next section I will look at several objects in and around the summer triangle.
If you are interested in finding these objects on your own then please consult the charts on my website. If you are unfamiliar with using astronomical charts then you will benefit from my course on Star hopping. This is available from my website or YouTube.
The first objects we will look at are a pair of Open Clusters; M6 and M7. These are located on the border of Sagittarius and Scorpio near the “stinger” of the scorpion. They are both very bright (M7 being slightly brighter). In a dark sky they should be visible with the naked eye. In the photo M6 is the higher of the two clusters.
An Open cluster is a group of stars that happened to be created in the same place and at nearly the same time. The stars are not gravitationally bound to each other so, in time, they will drift apart. The clouds of dust we talked about in the first section are the fuel of star formation. We will look at one area where star formation is occurring in a moment.
M6 is relatively close at 1,600 light years away and is about 12 light-years across. Like most open clusters it is young at about 100 Million years.
M7 is slight closer than M6 at about 800-1000 light years and bigger (25 light years).
Our next object is located just to the left of the top star of the teapot and has the designation M22. M22 is another type of cluster called a globular cluster. Don’t let the similarity in the name fool you. This is an entirely different kind of object than an open cluster. For one Globulars are tight balls that are gravitationally bound unlike an OC in which the stars just happen to be in the same area. Other differences are globulars are old and very far away.
M22 is 10,400 light years away. For a globular cluster that is close! It is estimated that M22 consists of as many as 70,000 stars packed into about 100 light years. It is the brightest globular visible from the northern US.
Most Globular clusters are fossils. They formed early in the life of the universe. The stars in globular cluster seem to follow different rules than “normal” stars. Their chemistry’s indicate that they are mostly first generation and do not contain the byproducts of past supernova. However, stars of this kind should not burn as long as the stars in globular clusters seem to have. This is an area of active research. For more information see the Further Reading section in the credits.
Many if not most of the current generation of large galaxies have a halo of globular clusters that surround them. Presumably the ones near our galaxy are orbiting the center of the Milky Way, but the dense dust and stars of the central bulge prevent us from seeing any GCs in transit through the center.
A variety of instruments (including the author’s own telescope) can also be used to observe GC surrounding other galaxies. M31 has several that can be observed with a large amateur telescope.
The next two objects are located above the spout of the Sagittarius teapot. In the darkest skies these are visual objects, but in most locations you will have to perform a very easy search.
Located close to each other are the two bright nebulas M8 and M20.
The southern most object (lower in this picture) is M8. M8 is a star forming region about 5200 light years from earth. In the distant future it will produce an open cluster like M6 and M7 we looked at earlier. The young cluster NGC 6536 is already visible.
The glow that you see is caused by the same effect that causes fluorescent lights to glow. The emissions from one or more high energy stars are causing an area of gas to compress and glow. This in turn is starting new stars to form in the gas cloud.
M8 is a combination of bright nebula, dark nebula (where the star forming is occurring) and open cluster. It is an object worthy of more than a quick glance.
Located just north of M8 (higher in the picture) is another interesting nebula M20. This is another star forming region about 5200 light years away. The bright nebula is a combination of emission nebula (where the gas is glowing), reflection nebula (where light of some other glowing object is being reflected), a dark nebula which is clouds of dust, and an open cluster (the result of the star formation). The most distinctive feature is that the bright areas appear to be divided into three sections by dark bands (from which its common name Trifid is derived).
This is another stellar nursery. The Caltech website in the credits uses different wavelengths of light to break apart the various pieces of the nebula and discusses what can be seen using different parts of the spectrum.
Located north east of the main part of Sagittarius and above the bright patch of stars known as M24 is another star forming nebula M17.
M17 is known for its distinctive shape. Most locally call it the Swan, but it has other common names.
The stars causing the nebula to glow are hidden by the nebula. Thus what you see in the telescope is a bright glowing patch.
Since the nebula contains a lot of hydrogen gas it glows brightly in red. Unfortunately that shade of red is beyond human color vision. For us the nebula is either gray or it might appear to be bluish green.
We think the nebula is between 5000 and 6000 light years away.
Continuing north on the Milky Way we are going to leave Sagittarius. Located just above M17 is M16. M16 is another combination Open Cluster and Nebula.
The Open Cluster will be easily visible with binoculars or a small telescope. The nebula will be more of a challenge. This photo uses the red Hydrogen Alpha color which shows both the open cluster and the harder to see nebula.
The bumps are the location of the most famous of all Hubble pictures – The pillars of creation.
These show a star forming region close up. Please keep in mind that, like many Hubble pictures, this is a false color picture and not what you would see with your eyes.
While the Open Cluster is easy to see the nebula is very dim. In a small telescope the pillars of creation will likely not be visible. With a larger scope (15” or greater) you can observe the nebula. Unfortunately the hydrogen alpha glow is too red for our eye sight.; however it is visible using a filter that only passes a different type of light called Oxygen III or (O with the Roman numeral 3). Our eyes can see that shade of greenish light. The filter will remove other light that obscures the view of the nebula. Using a filter the pillars will just be visible.
That concludes our tour of the Sagittarius region of the summer sky. I have only focused on the brightest objects. There are many other objects with interesting stories. I have included a couple of others in the credits.
In the next section of the video I will follow the
Welcome to the third section of my video on the summer sky.
In this section of the video I will introduce you to some interesting objects
near the summer triangle. The summer triangle passes directly overhead at the
latitudes of the
Most of the objects I will show here are dimmer and smaller than in the previous section. To see all of the objects you will need a small telescope. The two clusters can also be seen easily with binoculars.
If you are interested in finding these objects on your own then please consult the charts on my website. If you are unfamiliar with using astronomical charts then you will benefit from my course on Star hopping. This is available from my website or YouTube.
The first object we will look at is the open cluster M11. It is located in the constellation Scutum which is between the summer triangle and Sagittarius. When I find it I start with Altair which is the southern star (lower right in this picture). M11 is not in this field of view so let me shift to another photo that shows M11
This shows the Milky Way below Altair which is on the left.
M11 is in a distinctive loop of stars. Start with Altair and trace the Milky Way to the south.
The common name for M11 is the Wild Duck Cluster. The Wild Duck is one of the Open Clusters that I like. The bright star in the center of the cluster makes this very distinctive.I will leave it to your imagination whether this looks like a duck or not
This cluster is nearly 220 million years old which makes it much older than the Sagittarius clusters described earlier.
The cluster contains more than 500 stars visible with a small telescope. This gives it the dense appearance of a globular cluster. It is not. Like the earlier open clusters this was originally a dust cloud. The vast expanse of time has allowed what remains of the original cloud to disperse.
It is estimated this is 6200 light years away.
Let’s move closer to the summer triangle and look at objects in and around it.
Let’s return to the summer triangle again. At the time of this picture the triangle was in the east. Remember this group of stars passes directly overhead and is then in the western sky. When that happens, Vega will be at the bottom instead of at the top.
In the previous section we talked about how stars formed. Now let’s see what happens when stars die.
One of the most spectacular examples of what happens is the dumbbell nebula (which is Messier Object 27). This is called a planetary nebula. An unfortunate name since they have nothing to do with planets, but Herschel thought that most looked like Uranus which he had just discovered. The name stuck.
Planetary nebula are formed when a sun with a mass less than 8 times the sun reaches the end of its life. The short description is that the star puffs out the outer layers of its atmosphere. What is left provides an energy source that causes the gas to glow. The full story is beyond the scope of this video, but is explained in detail in the credits for this movie. Of course if there were any planets revolving around this sun they were vaporized.
M27 is the result of one such star death.
The distance to M27 is not known with certainty. Estimates reach from 490 to 3500 light years, but 1250 light years is considered the best current estimate.
The physics of this type of nebula cause them to glow brightest in the green color of Oxygen III. Hence amateur astronomers frequently use a filter that only admits this green light so the nebula stands out better.
What if a star is bigger than 8 times the size of the sun? Those stars have a more dramatic end awaiting them. The next object is an example of this.
Between 5000 and 8000 years ago a large bluish star about 1,400 to 2,600 light years away came to the end of its life. In an instant it produced a blast bright enough that it will be seen in other galaxies (when the light gets there). The star shredded itself spewing its debris in a growing blast pattern. In the process it created the heavier elements. The elements in our bodies are the debris of such an explosion.
The debris is more formally called a Supernova Remnant. The most famous SNR is M1 the crab nebula which was observed blowing up in 1054AD. The SNR from the Veil explosion now covers a 3 x 3 degree section of the sky. That is 36 times the area of the full moon. It is so large that it was assigned several catalog numbers (NGC 6960/92/95).
This photograph is of the west section designated 6960. This is located near the star 52 Cygnus. This star is bright enough to see with your naked eye in a dark site.
To see this object you will have to use a telescope and an O III filter. A scope so equipped will be treated to a view much like what you see in this picture.
Earlier we discussed the planetary nebula M27. Another spectacular summer planetary is M 57 (the ring nebula). This is located close to Vega between two bright stars (beta and gamma Lyra).
Like M27 this was formed when a dying star shot off its outer layers. In this case most of the blast was at right angle to the earth. Thus we see a clear blast ring (although recent research suggests we are looking into a cylinder instead of a ring).
This is by far the smallest object. It is only about 3 minutes of arc across (roughly 1/20 of a degree). You will definitely need a telescope to see it.
Current thinking is that the ring is 2,300 ly from earth, but this is an area of active research.
The last object we will look at is located in the constellation Hercules. This is west of Vega and the rest of the summer triangle. This photo shows what the constellation will look like after midnight in July.
Hercules contains a keystone shape. On the west side of the keystone is located the Globular cluster M13
Unlike M22 which is low in the sky in the
Messier 13’s 100,000 stars makes it a bright, easy target for binoculars. It has been reported to be a visual object in pristine skies (probably also requiring teenaged eyes). While M22 is technically slightly brighter, M13 is set off by a dark background and rises higher in the sky.
M13 is another member of the globular halo discussed in the previous section. In this case the object is more than 25,000 light years away. It’s diameter is almost 145 light years (or 33 times the distance to the nearest star).
M13 is an ancient object. The current estimate is that it is 10.9±1.4 billion years old. That would mean that it was formed within the first few billion years of the galaxy or about 6 billion years before the earth was.
This concludes our look at the summer sky. See my web site for additional information on astronomy and for future videos.
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Copyright © 2009 Robert J. Hawley ALL RIGHTS RESERVED