After Dark

Milky Way in clear skies in remote America

When the sun’s light completely recedes, I bet you had no idea that with your naked eyes or a pair of inexpensive binoculars you can gaze upon constellations, nebulas, star clusters, planets, double stars, and even one galaxy that is only two million light-years away.  With summer approaching many might be traveling west to our National Parks where very little to no extraneous light washes out the splendor of our night-time cosmos.  This post is Part One of a three-part series.  Check back later for part two.

Our moon is one of the brightest objects to gaze, however, there are many others.  Our surrounding atmosphere has several phenomena and all the planets can be seen with the naked eye or binoculars except Pluto.  Asteroids, meteors, and comets can be detected as well.  And even further away you can spot star clusters, nebulas, and constellations including that one galaxy 2-million light-years away.  Yet, most star-gazers do not realize there is a nightly twilight phenomena which is closer than our moon.  It is closer than our own atmosphere.  It is Earth’s shadow.

Just as the Sun sets look opposite of it (easterly) close on the horizon.  Within minutes you will start to see a dark blue band begin to rise just above the horizon.  This is when the band is darkest.  As it starts to move upward, it will fade, until it disappears into the night sky at the ending of twilight.  This dark band marks the edge of the shadow of Earth’s horizon.  Red light from our Sun illuminates our atmosphere above the band.  The band is blue due to the blue part of sunlight which has been scattered into the shadow by dust particles.  If you see Earth’s shadow vividly, then there is little dust or humidity in the air.

We are of course inside the Milky Way galaxy.  The Milky Way is approximately 80,000 to 100,000 light-years across!  Our Sun rests 30,000 to 35,000 light-years from the center.  There are more than 1,000 clusters of stars within our galaxy, all of which are easily visible with binoculars.  Beyond the Milky Way is a bunch of empty space, and then a lot more galaxies.  The Milky Way is part of a group of galaxies called the Local Group and the flagship of this group is the Great Andromeda Galaxy.  The Andromeda Galaxy is so large and massive that it is the only galaxy we can see with the naked eye.  Out beyond our Local Group are more clusters of galaxies, as many as you could ever count in 50 lifetimes!  In fact, it makes no difference what direction you look with whatever size telescope you view, all you can see are galaxy upon galaxies.

Stargazing Basics

Visible Stars TableOne or three nights of viewing the night sky will not turn you into an expert astronomer.  However, there are four basic principles to help you and your fellow sky troopers understand what you’re viewing in the after hours.

BRIGHTNESS  The brightness of a particular star is measured by its magnitude.  Its magnitude is governed by how bright it actually is and how far away it is from Earth.  The brightest star in our night sky, Sirius, shines at a magnitude of 1.4, but its actual brightness is much less.  It is less because it is very close to Earth, just a mere 8.2 light-years away.  How exactly is magnitude determined?  It depends on your location.  If you are inside or near a large city, your 22 visible stars will be only a 1-magnitude or brighter.  On average, stars of the 2nd magnitude are actually 2.5 times dimmer than those of the 1st magnitude, and so on down the line.  In a moderately dark sky, you can view stars of about the 5th magnitude.  On super dark nights (no moon) we can most likely find 6th and 7th magnitude stars (see table above).

COLOR  A star’s color can reveal a lot about its nature.  Generally speaking, the more blue a star appears, the hotter it is, and the redder it is, the cooler it is.  We typically do not see stars easily with our naked eye, but the colors are a lot more obvious through binoculars.  And kids see star colors a lot better than adults.

EVERYTHING’S MOVING  It takes at least 15 minutes for our eyes to adjust to the darkness.  During that time, pick the brightest object you can see near one of the horizons.  Take note of its position relative to a tall tree, mountaintop, or building.  Once your eyes have adjusted, notice the object is moving up if you’re looking east, down if you’re looking west, or mostly left to right if you’re looking south.

DISTANCE  Because outer space is so unimaginably vast, it makes little sense to measure distances in miles or kilometers.  Instead, astronomers use how far the speed of light travels in an amount of time.  The Moon is about 240,000 miles away, but astronomers say it is 1 1/3 light-seconds away.  Our Sun is 93,000,000 miles away, but 500 light-seconds, or 8 1/2 light-minutes away.  When Jupiter is closest to Earth, it is 35 light-minutes away; in other words, when its reflection reaches us we are seeing 35 minutes into Jupiter’s past.  Now here is a mind-blower:  astronomers have determined that our Universe is approximately 13.8 billion years old.  What this means is we cannot see any further than 13.8 billion light years beyond Earth, because the light from whatever’s farther out hasn’t had time to reach our eyes yet!

Celestial Assembly

Looking up into the night sky it seems as if everything is painted onto an enormous black sphere that’s far away.  Astronomers call this the celestial sphere and find positions on it in similar ways we denote positions here on Earth.  There is a celestial equator too, just like the Earth’s equator but projected up onto the celestial sphere.

Image courtesy of burro.astr.cwru.edu

Seasonal Big Dipper. Image courtesy of burro.astr.cwru.edu

As mentioned earlier, objects appearing to move in the sky from night to night (or, in the case of meteors and man-made satellites, a lot faster), are all inside our Solar System.  To us, our Sun appears to move across the sky along a line we call the ecliptic.  This term is used because eclipses of the Sun and Moon are related to this line.  Tomorrow evening April 25th, 2013 there is a partial lunar eclipse.  Since the nine planets all move in nearly the same plane as the Earth’s orbit around the Sun, they too appear to move about the night sky near the ecliptic.  This is why on star maps they include the ecliptic as the narrow yellow belt.

Most modern astronomers do not use identifiable constellations such as the Big Dipper or Little Dipper to locate objects.  There are 88 recognized constellations that divide up the sky, many of which we never see here in the United States.  They are too far south.  Here in the northern hemisphere there is about 25% of the sky that is invisible to us.  For example, Americans cannot see the Southern Cross.  Only people close to the equator in tropical latitudes in the northern hemisphere can view the Southern Cross for a few brief hours during winter and spring.  Conversely, for viewers in places like Australia, they never see the northernmost 25% of our sky or the Big and Little Dippers which Ferris-wheel around Polaris, the North Star.

Cassiopeia as seen by naked eye

Cassiopeia as seen by naked eye

Just as southern constellations never rise above our horizon, others never set.  Even when the day’s Sun is drowning out the stars, there are constellations which despite the season never vanish.  These are called circumpolar constellations.  As seen in the image above, the Big Dipper is always visible to us in the northern hemisphere 24/7.  During the Fall it is just above the horizon and in Spring highest above the horizon.  For thousands of years ancient travelers of both land and sea used these circumpolar anchors to guide their way.  They too used the “dippers” to orient themselves, but often they included the constellation CassiopeiaCassiopeia is always opposite the Big Dipper and is noted for its “W” shape.

Most all of the constellations tell a story, a mythical story of the ancients.  This is why so many are fond of astronomy and stargazing:  you can impress your friends with stories of gods and goddesses behaving badly or saving mankind.

Well before the time of TV and video games, ancient cultures had to find their amusement wherever they could.  These myths, given by the stars to mankind, were most definitely the plots and schemes of the first “soap operas.”  Because most of Earth’s landmass lies in the northern hemisphere, the southern constellations represent scientific tools which seafaring navigators used.  And, of course, the 12 constellations that hug our ecliptic are the signs of the zodiac in astrology.

Some constellation figures like the Egyptian Orion, are fairly convenient to recognize, and others are simply “gap-fillers.”  And despite those old stories reminding us of a bunch of angry child-like behaving deities, they are fun to share and find in the night sky.  They connect us to our distant past.  And if your friends, spouse or romantic lover isn’t that impressed by your vast knowledge of the sky, these cultural backgrounds are certainly justification for learning the constellations.  No one should presume they can actually trace out a “reclining virgin” (aroused for an evening) when you are looking at the constellation Virgo!  One must know what you are looking at and how to find it if you are to be a true romantic lover!

* * * * * * * * * *

In Part Two of this series, I will give a quick guide to the remarkable celestial shows and events arriving between 2013 and 2015.  Grab your drinks, popcorn, lounge-chairs, and stargazing buddy.  It’s going to be quite a show!

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2 thoughts on “After Dark

  1. Didn’t know you were into astronomy. This reminds me of my kids’ science class last year. We learned (a little bit) about all of this stuff. And watched a lot of Bill Nye. 😉 Have you seen my older post, “what orion said”?

    I’m kind of a star and moon freak, though I don’t think much of astrology.

    p.s. I love Cassiopeia.

    Like

    • I’m a bit nerdy when it comes to science and yes, I love everything & anything about mother Earth, moon, our Solar System, and the cosmos. As a kid I use to draw & sketch out future space colonies & how people would live their daily lives in outer space. What would they need? Fun!

      I am definitely droppin’ over to read What Orion said! Cassiopeia, huh?

      Like

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