Why is the sky important?

We often don’t think about the sky above us as a part of the ecosystem other than when weather is involved. But it is! People have used stars and other objects in the sky for thousands and thousands of years to help them navigate, tell time, know when to plant crops, and create folklore and art. In fact, many animals use the sky for travelling and telling time!

Of course, the sky is also home to our Moon, an important force in many aspects of life on Earth. The Sun is also a vital part of life, as it gives energy to the planet.

Learn with us, with help from Jeff Hutton, an avid astronomer and Berea community member, about the sky above us and how it connects to the ecosystem and ourselves.

Click HERE for astronomical activities Jeff has written and shared with us.

April Skies over the Pinnacles

April’s four principal phases of the moon

 

Spreading Light
The first big number that I remember committing to memory was 186,000, as in the
speed of light through the vacuum of space is 186,000 miles-per-second. It seemed
cool to be able to recite the figure and it helped me to visualize just how far away things
in the night sky really were!

Then I discovered prisms, those thick wedge-shaped pieces of glass that you could
hold in a sun beam just-so and produce a little rainbow colored patch of light on the wall
or even the cat!

 

Ok. So how do prisms separate the white light from the Sun into the beautiful colors we
see? The technical term for these prism-produced colors is a spectrum. (The plural of
spectrum is spectra.) When white light shines at an angle through something denser
than the air, like the glass in my prism, in the words of Bart Simpson, it gets bent! It
bends because it is slowed down just below its normal speed. Not all of the colors slow
down the same amount, so they separate into the separate colors of the spectrum.
Red is ‘bent’ more than the blue when it passes through the prism.

 

Astronomers discovered that when they carefully analyzed the spectrum of a distant
star after it passed through a prism they could uncover clues about it’s composition,
how fast it was spinning, even how fast it was traveling through space. In fact, the
astronomer Edwin Hubble is credited in discovering that the universe is expanding
using the new science of spectrography, or analysis of stellar spectra!

No, this isn’t a picture of Edwin Hubble. It’s Henrietta Swan Leavitt. In 1908 Leavitt
published her own findings about determining the distances to stars. Hubble used her
findings on which to base his own discoveries. Leavitt wasn’t given credit, until now, for
revealing the basis of one of the greatest discoveries in astronomy.
The month of April is a usually tough one to observe the night sky. Daylight Savings
Time (or, as I call it, Government Nuisance Time) shifts our schedule to make the sun
seem to set later. Stormy weather often tears up our plans to observe the clear night
sky. But we shouldn’t miss some wonderful opportunities to appreciate the colorful
show offered up by wind and weather.

Let’s Talk Rainbows!
There’s a lot to know about rainbows but the most important thing is to pause and
marvel at them when they appear, usually after a good rain. It’s also fun and interesting
to know a little about them. Before you can see a rainbow a few things must happen.
1. The sun needs to be shining brightly and be close to the horizon. 2. The area of sky
opposite the sun must be full of raindrops: as many and as big as possible.

 

Usually raindrops are drawn looking like the teardrop shape on the left panel but while
they are falling from the sky they form little watery balls like the illustration at the right.
It turns out that this spherical shape acts like a glass prism.

 

 

When white sunlight enters a raindrop at just
the right place, seen here at the upper-right,
it enters the watery droplet which is denser
than the surrounding air. This causes the
sunbeam to separate into its colors. Then it
reflects off the inside of the droplet. This
magnifies the color separation. Finally, the
separate colors exit near the bottom of the
droplet and this separates the colors even
further!

 

 

 

 

 

Did you ever notice that the rainbow seems to follow you, even if you’re moving down
the road in a car? (Drivers, let your passengers look. You keep driving safely!)
This is because the rainbow you are seeing is made up of parts of millions of little
spectra from millions of little raindrops.
Have you ever seen a double rainbow? The second rainbow is seen outside the first
rainbow, and is a little fainter, pictured below. Only part of each rainbow is seen in this
image.

Each raindrop really makes two
little spectra. The white arrows
represent the white sunlight
entering the raindrop. The
sunbeam on top produces the
primary rainbow and the sunbeam
at bottom produces the secondary
rainbow. The reason the
secondary rainbow is fainter is
because the sunbeam at the
bottom has to reflect twice inside
the raindrop before exiting as a
spectrum. Some light is lost in
each ‘bounce’. This is why the
colors of the secondary rainbow
are reversed.

 

We see rainbows because pieces of the spectra from each little raindrop enter our eyes
at just the right angle! When you are standing right next to your best friend, admiring a
beautiful rainbow think about this: you are both having a slightly different view of the
gorgeous colors. You are seeing your own separate rainbows from different sets of
water droplets!

This is how we see rainbows.
Speaking of sunbeams, Have you ever noticed a spray of sunlight sneaking through a
hole in a cloud? Maybe you’ve noticed a thick cloud in a clear sky that happens to be
covering the sun like this:

It’s pretty but this picture is also an illusion, something that isn’t what it appears to be.
The sunbeams (the scientific term is crepuscular rays) look like they are spreading out
from the hidden sun like the spokes of a wheel. The rays are actually parallel.

The illustration on the left shows what the rays are actually doing and the illustration on
the right shows what you see. Of course the bright rays are mainly fine dust particles in
the air that are lit by sunlight. If these rays are intense enough to go all the way from
the sun’s location in the sky they can all meet up again at a point in the sky that is
opposite from the sun. That’s called the anti-solar point.

A way to visualize this is to go outside on a sunny day. The shadow of your head is at
the anti-solar point!

In this picture the anti-solar point appears just above the house, on the horizon. Since
these rays are converging they are called anti-crepuscular rays. The sun was at the
photographer’s back. Remember, these rays are actually parallel to each other!

To tie this all together, here’s a picture I took a few years ago that shows anti-
crepuscular rays that also provide the light for a partial rainbow.

Think of a rainbow like it like the rim of a wheel. The center of the wheel is at the anti-
solar point.

In this illustration, the Sun is just setting on the western horizon so the anti-solar point
is on the eastern horizon. Remember that a rainbow always has the anti-solar point at
its center. If the sun is too high after a rainstorm, you may not see a rainbow at all
because the anti-solar point is too far below the horizon.

Back to Space
One of the most interesting things to appear in March skies was the apparent close
approach of the planet Mars to the beautiful cluster of newborn stars called the
Pleiades. On March 6, I was able to take the picture below. The inset picture was
taken in April of last year with the much brighter planet Venus.

 

Attractions in April

April 5
If you’re up before dawn, take in a very pretty sight of the Moon, Jupiter
and Saturn, neatly lined up low in the southeast before the sun’s glare
fades the sky to blue. Look again the next day. What’s changed?

April 16
Here’s an easy way to learn the location of the constellation, Taurus, the
Bull. Go out as soon as it’s dark and find the crescent Moon, between the
horns of the bull. I wonder if a similar event inspired the ancient
Egyptians to invent the bull-god Apis? A statue of Apis is on the right.

April 20
Binocular alert! Get your binoculars or small telescope out and find the
Moon and look below and to the right to find the “Beehive”. That’s a nice
little cluster of stars in the constellation Cancer. This cluster is around
600 light-years away and is about as old as the Earth, 4 billion years.
Other sources suggest it is younger: about 600 million years old. Another
name for the “Beehive Cluster” is Praesepe. That’s Latin for ‘cradle’. Two
planets have been identified circling stars in this cluster.

April 22
The annual Lyrid meteor shower makes a return appearance Sometimes
we get a really good show of “shooting stars” from this shower, sometimes
not. As always, it’s best to set your alarm for about 3:30 AM, brew some
coffee or heat some hot chocolate and head outside to a dark area away
from lights. Dress warm! See my suggestions on viewing meteor
showers in previous articles.

 

For more detailed celestial information, check out skyandtelescope.org.

Click Here for a pdf version

Keep Looking Up!

Jeff

 

Click HERE for fun and educational astronomy activities provided by Jeff Hutton!

Thanks to Jeff Hutton! Jeff is a long time amateur astronomer and telescope builder. He hopes to resume offering monthly presentations on astronomy and related topics at the FOC soon!