Exploring Deep Space—Galaxies!

scope on the skies

Exploring Deep Space—Galaxies!

Science Scope—January/February 2022 (Volume 45, Issue 3)

By Bob Riddle

Figure 1 Local group and nearest galaxies. — Figure 1

We all know that our solar system is part of a much, much larger collection of hundreds of millions of stars that are mixed with dust, gases, and stuff we do not know much about into a spiral shape we call the Milky Way Galaxy. This is a huge shape at approximately 100,000 light years in diameter, but there are other galaxies whose size dwarfs our galaxy, and there are even dwarf galaxies. So, in this column we are going to explore the universe of galaxies by going deep—deep as in “Deep Space.” What is Deep Space? Deep Space is mostly described as the region of the space beyond the Earth–Moon system. Quite frankly, that is a lot of space, but it seems to suggest Deep Space is within the solar system. Think bigger. Even though the solar system, from our perspective in the inner solar system “looking outward,” is seemingly large, it is not large from the perspective of the scale of the known universe. For me, Deep Space is beyond our solar system, even beyond the edges of our galaxy. It is the rest of the universe, seen and unseen, that our galaxy, the Milky Way, is a part of. And our galaxy is not alone, as the Milky Way belongs to the Local Group (see Figure 1) of galaxies that we share with our portion of the universe, which in turn is part of a cluster of groups of galaxies, and so on.

Imagine a place where nearly all of the points of light are not stars, but individual galaxies. In the Hubble Deep Field Image of a region of the sky, thousands of galaxies were revealed showing a variety of shapes, sizes, and interactions (see Figure 2). An interesting and appropriate statement about galaxies is that when we see a galaxy and determine its distance, we know that we see it not as it is today but as it once was. Students will learn that distance in light years is the same as the time it took for that light to reach the Earth. For example, the light we see from a galaxy that is 10,000,000 light years distant took 10,000,000 years to reach the Earth. We would have to wait another 10,000,000 years to see today’s light from that galaxy! Like someone has said more than once: You can’t imagine the magnitude of the situation.

Figure 2 Hubble deep field image. — Figure 2

A good way to start with your students on a journey outward would be by watching some short videos that will set the stage for exploring Deep Space and give them a sense of the known and estimated size and age of the universe. Begin with an old classic, the original “Powers of Ten” (see Videos section in Online Resources), a short video that starts with a couple having a picnic outlined with a square that is one meter wide. As the video progresses at 10-second intervals, the view zooms outward at increasing size that is 10 times farther and 10 times wider than the previous view—for example, 10 meters (10¹ meters), 100 meters (10² meters), 1,000 meters (10³ meters), one light year (10¹⁶ meters), and so on—until arriving at the farthest known distant celestial objects at 100,000,000 light years (10²⁴ meters). The process is then reversed, but instead of stopping at the one square meter, the view decreases in size at intervals of negative powers of ten. This time the view stops at the smallest size, 0.00001 angstroms wide (10^-15 meters), of objects known at the time—quarks. Keep in mind that this video was based on what was known or suspected in 1977.

There is a relatively more modern version of the “Powers of Ten” titled “Scales of the Universe in Powers of Ten” (see Videos section in Online Resources) produced in 1996 by IMAX and narrated by Morgan Freeman. This cosmic journey is based on the same idea, except that a circle is used rather than a square and the video takes us outward to a circle 10,000,000,000 light years wide (10²⁶ meters). Then like its video predecessor, it takes us inward, but this time the images zoom inward on a drop of water, each time 10 times smaller, but also ending at the realm of quarks, 10^-15 meters.

To help students understand and visualize the range of galaxies in terms of shape, size, age, and distance, you can show students two short videos that explore galaxies, both of which are based on real images and data. Using an image from the Great Observatories Origins Deep Survey (GOODS; see Online Resources), the video “Ultra-Deep Field: Looking Out into Space, Looking Back into Time” (see Videos section in Online Resources) in a few minutes takes a 3-D journey through the vastness of space looking at the many varieties of galaxies, while the shorter video “Hubble: Galaxies across Space and Time” (see Videos section in Online Resources), produced by IMAX, shows how the appearance of galaxies differ as distance increases. Nearby galaxies are more completely formed and better developed in terms of their spiral shape than more distant galaxies, or as this video describes them, they are more “disheveled.” Remember, we see galaxies as they once were, not as they are, so well-developed and relatively closer spiral-shaped galaxies, for example, are younger than the more distant disheveled-appearing older galaxies. As spiral galaxies age, they go through changes in their structure and appearance due to a variety of causes, including the merger and interaction with another galaxy, the growth of a black hole, or even a merger of black holes (see Image Archive: Galaxies in Online Resources). Keep this in mind, as students may select galaxies based on their shape. The shapes students may be attracted to besides the face-on spiral galaxies are possibly those referred to as Peculiar Galaxies. This could be a pair of galaxies in the process of merging with distorted shapes, or a galaxy appearance distorted through a process called gravitational microlensing (see Online Resources). Whatever galaxy a student chooses, the student should be encouraged to learn more about how that galaxy came to look as we see it now and what it may look like in the future.

Finding images

There are many opportunities for students to learn more about galaxies that include requesting images from a remotely controlled telescope and examining images of our universe taken by both land- and orbital-based large aperture telescopes. Students could “browse” the universe using the Explore Our Universe Skymap (see Online Resources) to start their galaxy search.

Another option could be taking part in a Citizen Science Project or NASA Challenge event. Most recently, during the summer of 2021, NASA hosted the annual Astrophoto Challenges, offering two different directions for students to follow as they studied the spiral galaxy M-87. One option was the MicroObservatory Challenge, and the other was the NASA Data Challenge. Although those challenges have ended, students can still visit the website to explore the entries submitted by student participants or to try the challenges themselves. Information and links to the challenges are on the Observing with NASA website home page (see Online Resources). Students may also make their own image requests of galaxies as well as any visible planet, our Moon, and the Sun. Then using the online image processing, they can analyze those pictures. (Note: an e-mail address is required to receive the images.)

Online sources for images taken by land- and orbital-based telescopes vary in how they operate, but all have images taken in a variety of wavelengths, offering a chance to view different details in an image. Students can explore how objects differ when viewed through different wavelengths at the NASA Explore Light interactive web page (see Online Resources).

Of the many options for obtaining images of celestial objects, the Aladin Lite online or downloadable program is one of the easiest to use. This is an interactive atlas of the sky that is connected to several databases of astronomical imagery and data. The Aladin Lite home page opens with a color view of the region around the “belt stars” and the Horsehead Nebula taken by the Deep Sky Survey 2 (DSS2; see Figure 3). Using that view or an object selected by the student, you can cycle through several telescope surveys that show the object in different wavelengths including visible light, X-ray, hydrogen alpha, and infrared. With most objects the difference in detail is striking.

Other online sources of imagery and data include the Sloan Digital Sky Survey/Sky Server (SDSS) where students can search for objects by the object’s ID or by location. A quick way to access images taken by the SDSS telescope is by clicking on the Famous Places link. This will present a graphical list of objects seen by the Sloan telescope. The European Southern Observatory (ESO) maintains an Image Archive that includes some spectacular images of galaxies and clusters of galaxies (see Image Archive: Galaxies in Online Resources). If looking at online pictures of galaxies and other deep sky objects piques your students’ interest, there may be an observatory nearby for real sky observing (see Observatories: USA and Observatories: Globe in Online Resources).

Have a stack of unused CDs laying around? If you do, check out Universe of Galaxies (see Online Resources) to see how to put those CDs to a good use in an activity that models the relative distances between the Milky Way Galaxy and other galaxies. Galaxies are made up of many things, chief of which are the stars that come together gravitationally. Students can learn about the lifecycle of stars by taking part in an online star party with Infiniscope’s interactive Star Party (see Online Resources).

Regardless of the online source used, a good practice for students is to keep a log of their observations; either the online or mobile version of Stellarium (see Online Resources) would be a good starting point. Stellarium is a planetarium-type program capable of showing the night or day sky and most celestial objects for one’s home location or other places on the Earth. Students could use this astronomy program to search for objects like a galaxy, or just see what is visible on a given evening. Additionally, the program has a feature called NoctuaSky, which allows users to keep a record or log of their efforts. (Note: Use of the log requires creating a user account.) Once an object has been located, the student could then use that information to find their object at one of the websites offering images in different wavelengths.

For students

Check out an e-book from the Hubble Digital E-Book Library to learn more about galaxies, the universe, and the Hubble Space Telescope.
Go to the Observe with NASA MicroObservatory (OWN) website and request images of galaxies. Use the online image processor to analyze your images.
Use the Aladin website to find images of a galaxy you are interested in. What structures or parts of the galaxy are seen or not seen with different wavelengths? With which wavelength does your galaxy look the best? Any idea why?
Galaxify your own message using galaxy shapes at the My Galaxy website (see Online Resources) or the Hubble website to find out what the Hubble Space Telescope saw on your birthday.

James Webb Space Telescope

As of this writing, the launch of the James Webb Space Telescope (JWST; see Online Resources) is scheduled for December 22, 2021, and once in orbit will be readied for operation after a few weeks of system checks. The JWST will not so much replace the Hubble Space Telescope (HST; see Online Resources) as add on to what the aging HST is capable of, plus doing much more. At the JWST website, there is an interactive resource where students can see how the two orbiting telescopes compare. •