Hello everyone, I’m Darrell Heath with UA Little Rock’s College of Arts, Letters, and Sciences,
welcome to The Night Sky.
With the arrival of Spring, stargazers bid farewell to the wintertime constellations
of Taurus, Orion, and Gemini and say hello to new arrivals such as Leo, Virgo, and Bootes.
But it’s more than just a changing of the guard, our whole view of the universe changes
as well. During Winter and Summer, the sky overhead offers us views of the inside of
our Milky Way Galaxy, but in Spring and Fall, the night sky is a window looking outside
of the galactic plane and into regions of space beyond the galaxy.
Spring is a great opportunity
to see dozens of different galaxies and galaxy clusters.
But what if you don’t own a large telescope? Are there still cool things to see? The answer
of course is ‘yes’. With just a pair of binoculars or a small backyard telescope (say,
anywhere from 2” to 6” aperture scopes) there are always a great many things that
one can see no matter what time of the year. In this episode of The Night Sky, I want to
offer the beginner stargazer who doesn’t yet happen to own a large telescope, or who
only has a pair of binoculars, the opportunity to get outside under a dark sky and see a
few amazing things on their own. I’ve selected 4 deep sky objects, some suited for binoculars
and some that are perhaps more suitable for a modest sized backyard telescope.
Now what do I mean by ‘deep sky objects’? Simply put, these are celestial objects that are
located outside of our own solar system. Objects such as star clusters, nebulae, and even other
galaxies.
If you don’t have a telescope of your own, be sure and check with your local library
to see if they might offer loaner scopes, many public libraries around the country currently
do so. To see if there are any libraries in your area that offer these kinds of programs,
just go to librarytelescopes.org . Your local astronomy club might also offer loaner scopes
or binoculars. If not, I bet that they offer star parties you might attend so that you
can look through various types and sizes of telescopes in order to see some of the objects
that I’ll be talking about. To find out where the closest astronomy club is to you,
just pay a visit to either the NASA Night Sky web site
(https://nightsky.jpl.nasa.gov) or the Astronomical League (https://www.astroleague.org).
Okay, if you’re ready, let’s get outside on a dark, moonless, spring night and begin
our sky tour.
In today’s technological world, many of us are familiar with GPS and a variety of
different digital assistants that can help us navigate to a specific location when we
are traveling. There are similar kinds
of computer technology that can guide our telescopes across the sky in order to help
us navigate our way around the heavens. But not all of us can afford these kinds of things
A common method than many astronomers have used for ages is known as
“star hopping”. Star hopping is nothing more than using familiar celestial signposts
to help guide us to other, more challenging objects. An easy example would be using the
two bright stars that make up the front end of the bowl of the Big Dipper in order to
guide your eye to the rather faint North Star, Polaris. The apparent distance between the
stars as we see them upon the sky, is usually measured off in angular degrees. For example,
if you draw a line from those two bowl stars, Merak and Dubhe, in the Big Dipper, you have
traced out a line of about 5 degrees. If you extend a line from Dubhe to Polaris, you’ve
now gone approximately 30 degrees. A useful way to measure the sky is literally right
at your fingertips. If you make a fist, extend it out to arm’s length, and then hold it
up to the sky, the distance across your fist is about 10 degrees. Extend your pinkie finger
out, the width of your pinkie is 1 degree. Extend your three middle fingers and you are
now measuring 5 degrees upon the sky. The distance between your extended pinkie and
your index finger is 15 degrees, while the distance between your pinkie and your thumb
will measure off 25 degrees.
I mentioned earlier how the spring sky is full of galaxies for the owner of large telescopes,
but that doesn’t mean that there aren’t any available to those of us who own binoculars
or small telescopes. On any clear, dark night (and from as dark a sky locale as you can
manage) go outside and face north to find the Big Dipper. Next, locate the star Phecda
(sometimes known as “Phad”), which makes up the lower left corner of the dipper’s
bowl. Extend a line from Phecda towards Dubhe, the star that forms the upper right corner
of the bowl. From Dubhe, continue that line out to about 7 degrees. With a pair of binoculars,
slowly scan around this part of the sky. You are looking for a relatively bright smudge
of light. When you find it, you have found Bode’s Galaxy, also known as Messier 81,
or just M81. This is a good place to stop for a reality check. Galaxies and nebulae
are never going to appear as the bright colorful photographs that you see on the internet or
in magazines, the human eye simply cannot absorb the number of photons that a camera
can with a long exposure photograph. Instead of expectations of Hubble-like images, just
keep in mind that, when you look through the eyepiece at these various deep sky objects,
that the light hitting your eye has traveled across vast oceans of both time and space
before being finally being absorbed by the retina in your eye. In that sense, you are
physically interacting with an object that is located thousands or even millions of light
years away.
While Messier 81 is going to appear as a bright, oval-shaped smudge of light in binoculars
and small telescopes, it is in fact a grand spiral galaxy that is some 90,000 light years
across and located almost 12 million light years from Earth. Like many spiral-shaped
galaxies, M81 has a high concentration of stars at its core. The combined glow from
all of these stars is what creates the bright nucleus that you are seeing in your binoculars
or telescope. And while you cannot see the spiral arms, you can detect their presence
in the form of the soft glow that creates the halo around the brighter core. It is in
the spiral arms that all of the galaxy’s gas and dust is to be found, the stuff from
which stars are born. Stars are scattered throughout the arms of the galaxy’s disc
and it is their combined light that creates the feeble glow of the halo. The galaxy was
first discovered in 1774 by the German astronomer Johann Bode. Bode also discovered another
galaxy right next to M81 and you can see it as well within the same field of view of your
binoculars or in a telescope with a low power eyepiece. How’s that? You get not one, but
two galaxies for the price of one.
The second galaxy is known as Messier 82, or, the Cigar Galaxy. Rather than having an
oval-shape, like M81, M82 is more spindle, or cigar-shaped. The reason for this is that
we are seeing the galaxy edge-on as opposed to M81’s nearly face-on view. As a consequence,
M82 appears a bit dimmer than its companion.
Both M81 and M82 are interacting gravitationally with one another and at some point in the past,
they must have had a very close encounter where the gravity of M81 strongly distorted M82.
This encounter also triggered a burst of star formation inside M82.
Moving right along, we are now going to look for the famous Whirlpool Galaxy, Messier 51,
in the constellation Canes Venatici. It’s pretty easy to find but because it has such
an overall low surface brightness, you really need dark skies with no moon to see it.
Just go the star Alkaid, the star that denotes the end of the handle of the Big Dipper.
About two degrees below the handle of the Dipper you’ll find a 4th magnitude star known as 24 Canum
Venaticorum. Two degrees to the right of Canum Venaticorum and you will find a smudge of
light that is M51. You can see the smudge in binoculars that magnify 10X, but in a small
telescope, things start to get really interesting. With 3” or 4” aperture scopes, you can
see the galaxy as an oval-shaped disc with a bright nucleus at the center.
But hold on. What’s this? Is that a faint tendril of light reaching out from the oval
towards a smaller oval? Yes, it is. That smaller oval is a tiny, compact galaxy known as NGC
5195 and that tendril is a stream of material that is being ripped away from M51 by NGC
5195. Over the next few hundreds of million years, the two galaxies will collide and fully
merge with one another. Interestingly, the Hubble Space Telescope was able to image the
core of M51 and the photograph reveals a curious-looking cross-shaped mark where the supermassive black
hole in this galaxy resides. Astronomers believe that the dark part of the X marks where a
100 light year diameter ring of dust, seen edge on, is obscuring our view to the black
hole’s accretion disk.
Just an additional cool thing to think about when observing M51.
Let’s move on from the interesting smudges of light to some very nice eye candy. We are
looking for an open cluster of stars located in the constellation of Cancer, known as “the
Beehive”, or Messier 44. Open star clusters are loose gatherings of stars that were all
born from the same cloud of gas and dust and are more or less bound to one another by their
mutual gravity. The cluster is somewhat dim as are the stars that make up the constellation
of Cancer, so we are going to use some bright stars from two other constellations to guide
us to it.
Find the stars of Gemini: Castor and Pollux. Castor is the star that is on the right (west)
and Pollux is the star on the left (east). Now, once you have found these two stars,
I want you to locate the bright star Regulus, the brightest star in the constellation of
Leo and which is located east of Gemini. If you draw an imaginary line from Pollux to
Regulus, then the Beehive is located about half way in between the two.
With binoculars of any size, this seemingly empty patch of sky suddenly blazes forth with
dozens of bright stars, shining like diamonds in the dark.
Most are white in color, but you will also
see a few that appear red or orange. What’s up with those? Well, those are higher mass
stars that are reaching the end of their lives. They have depleted their fuel supply of hydrogen
in their cores and have now swollen in size to become red giants.
Upon the sky, the Beehive Cluster spans 1.5 degrees across, that’s the same diameter
as three full moons placed side by side. All told, there are some 1,000 stars swarming
around inside the Beehive and their estimated distance from our own solar system is somewhere
around 520 to 610 light years away and is about 15 light years across.
While the Beehive is a fine example of an open cluster, a somewhat loose grouping of
stars that are bound to one another by gravity, there is a more compact type grouping of stars
known as a “globular cluster”. Globular clusters are massive, compact star clusters
that contain thousands or even millions of individual stars, their mutual gravity having
pulled the group into a spherical shape.
Our last object on this tour is a very fine example of a globular cluster and it’s known as Messier 3,
located in the constellation of Canes Venatici.
To find M3, just go outside on a dark spring night, and face the northern half of the sky.
We are looking for the bright orange star, Arcturus, fifth brightest star in the night
sky and located in the constellation of Bootes, the herdsman.
Use the Big Dipper and the mnemonic: “arc to Arcturus”. All you have to do
is extend the curve of the Big Dipper’s handle out in an imaginary line for about
25 or 30 degrees until you run into this bright star. Next, we need to return to the Big Dipper
and look under its handle for the small constellation of Canes Venatici, the hunting dogs of Bootes.
The brightest star of Canes Venatici is Cor Caroli. Draw another imaginary line from Cor
Caroli to Arcturus. Messier 3 is located about half way along this line. Use binoculars to
first locate it as a fuzzy looking star upon the sky. Binocular views of M3 will reveal
it as a softly glowing cotton ball of light, brighter towards the center than it is out
upon the fringes. You will need a telescope of at least 4” or 6” of aperture before
you can begin to resolve individual stars but it’s a splendid sight in any size telescope.
While you might see hundreds of individual stars in M3, astronomers estimate that there
could be more than half a million of them crammed within a sphere that’s spread across
some 200 light years.
Like many other globular clusters, M3 is very, very old.
Current estimates place Messier 3 at around 10 billion years old, almost as old as the universe itself.
Okay, that’s all for now. But before I go, if you are looking for a good book to help
you find some relatively easy targets upon the night sky, I’m going to recommend you
get a copy of “100 Things To See In The Night Sky” by Dean Regas, astronomer at
the Cincinnati Observatory and co-host of the syndicated show Star Gazers on PBS. Be
sure to check out our own Night Sky website each month where we feature a calendar of
monthly highlights as well as articles on specific celestial objects for you to observe
either naked eye or with binoculars or a small telescope.
Clear skies to you all and make sure that you take a little bit of time to step outside
and look up in both awe and wonder.