Category: general science

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Twilight

By Jay Ryan at Homeschool-articles.com

Twilight is that brief part of each day in between day and night, when the Sun’s rays light up the sky, but the Sun itself is below the horizon.  Dawn twilight is in the morning before sunrise, when the Sun’s glow chases away the night, when the early sky is tinged by Homer’s eos daktylos, “rosy-fingered dawn.”  Dusk twilight is on the other side of the day, when the ruddy glow of the sunset persists after the Sun itself has sunk below the horizon.

Twilight is my favorite time of day.  Twilight is a rare, precious part of each day, a brief period of perhaps 45 minutes separating the Sun’s rays of daylight and the full shadow of night.  Twilight is the most changeable part of the day.  Daytime offers a consistent blue sky as the Sun races from east to west.  Nighttime is uniformly dark, only distinguished by the rotation of the stars across the sky.  But during twilight, the sky quickly transitions from the brightness of day to the full darkness of night in less than an hour.

Twilight offers a range of colors — brilliant hues of red, yellow, pink and orange that rapidly change to deepening shades of blue.  After sunset, the first  stage of twilight is civil twilight, when the sky is very bright and the clouds are painted beautiful shades of color.  During civil twilight, the entire sky is lit up with the Sun’s light, and the land retains a dim daylight quality, though the Sun’s rays are not visible and shadows cannot be seen.  In the evening, civil twilight is the first stage of twilight after the sunset, and in the morning, the last stage before the sunrise.

In the evening after sunset, the next stage is nautical twilight, when the brightest stars begin to appear.  At this time, the streetlights begin to come on for most city dwellers.  The sky has lost most of it’s orange color, except perhaps for a fading patch to mark the place of Sun.  The sky has become a deep turquoise blue, brighter toward the Sun’s direction.  Nautical twilight is so-named because it is during this stage that sailors can first find the “navigator’s stars” used for finding direction at night.

The final stage of twilight after sunset is astronomical twilight.  At this stage, the sky grows ever darker, and the stars begin to come out in great numbers.  A dwindling patch of twilight remains along the horizon to mark the Sun’s position.  A keen eye will notice that this patch is not in the same place as the sunset, and indicates that the Sun has moved below the horizon since going down.  Twilight ends when the last patch of sunglow has vanished from the horizon, and full astronomical night commences.

Seasonal and Global Variations in Twilight
The length of twilight varies over the span of the year, and also with latitude around the earth.  In the springtime and autumn, near the equinoxes, twilight is shortest.  As seen from the ground, the Sun appears to follow a very direct path below the horizon after the sunset, and so the Sun and its rays quickly dip out of sight during the spring and fall.  As a result, night falls quickly near the equinoxes.
During the summer, the period of twilight is longest.  The Sun appears to take a slanting path toward the horizon.  The Sun follows a shallow path below the horizon, and a patch of astronomical twilight can be seen far from the place of the sunset, in some places longer than an hour after Sun’s disappearance, depending on location.

During the winter, the twilight is longer than at the equinoxes, but not as long as during the summer.  These changes in twilight result from the varying angle of the Earth’s axis to the Sun as the Earth follows its orbit around the Sun over the course of the year.

The length of twilight can vary considerably depending on latitude over the Earth.  Twilight is shortest at the Equator and longest at the North and South Poles.  On the Equator, the entire sky appears to lie on its side.  The Sun sets perpendicularly to the horizon, and drops quickly out of sight after sunset.
Therefore, the period of twilight is very short.  Vacationers and newcomers to the tropics such as new missionaries are often amazed at how quickly night falls in these warm latitudes.

In the temperate latitudes, where most of the world’s population resides, the Sun approaches the horizon at an angle.  Thus, the Sun takes a longer, slanted path as it dips below the horizon, and twilight takes a longer time to fall.  As one moves north or south toward the poles, the length of twilight increases.

At latitudes above 48 degrees, the “white nights” can be observed during the longest days of summer.  The evening twilight merges with the morning twilight so that some trace of daylight can be seen at midnight!  The white nights can be observed from the northern border of the continental USA, most of Canada, and places in northern Europe and Asia such as Great Britain and Russia.

In the polar regions, continuous daylight and nighttime persist for long periods of time.  However, around the equinoxes, the maximum global interval of twilight can be observed at the North and South Poles.  Each year, following the long polar summer, the Sun begins to set at the North Pole on the autumnal equinox, September 23, and finally sets two days later, on September 25.

The Sun goes through the stages of twilight over a span of several weeks, passing from civil twilight to nautical twilight and astronomical twilight.  Finally, on about November 15, the Sun has reached far enough below the horizon that twilight ends and full night commences!  Full darkness only lasts a couple months during the long polar night, and twilight commences once again around the end of January, and brightens steadily until the vernal equinox on March 21.

As the days warm up in your area, plan some outdoor activities during the evening twilight!  Make it a point to observe the stars as they appear one by one.  Be sure to bring plenty of bug spray!

Jay Ryan is the author of Signs & Seasons, an illustrated, Biblically-centered homeschool curriculum for Classical Astronomy. He is also the creator of the Classical Astronomy Update, an email astronomy newseltter especially for Christian homeschoolers.  Visit his website at ClassicalAstronomy.com.

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Studying Life Cycles and Processes: Your Pet

When you study animals in the home, you learn about many things. Not only do you learn about the structure of animals, their habits, and their usefulness to Man, but you learn about the responsibility of having to care for a pet. You learn about illnesses, safety, dependency and friendship.  These are the reasons why so many of us have pets in our homes.

The idea of using your pet as a science topic has probably occurred to many homeschoolers, and so, here are some ideas which may help you “pull it all together” for homeschool.

Because there are so many individual things to learn about animals, zoologists have generalized. Generalization involves using the similarities of organisms to study them together in groups. In this way we might ignore the differences between animals and merely note that they all move in some way.

Animals have motion systems. Some use muscles, others use hydraulic systems, but they all have a generalized motion system. How are the motion systems different? How are they alike? There is a whole branch of zoology called comparative anatomy specializing in making these kind of comparisons.

One thing all living organisms have is a life cycle. We usually study life cycles when we study insects, especially the butterfly, and we all remember learning about caterpillars, pupae, and cocoons.

An excellent way to study life forms is to investigate their life cycles. Most of them are easier than insects to observe, it just takes longer. In the study of life cycles, a generalized cycle can be applied to most animals.

There are three basic processes of life in this cycle: Intake, growth, reproduction. These are all processes instead of stages, but they define what is taking place within the life cycles of any particular organism.

Intake is the taking in of nutrients necessary for growth and reproduction.  

Growth is the use of the nutrients to increase in size and maturity.  

Reproduction is the continuation of the species, which can only occur after a certain level of growth and maturity has taken place.

Failure of the organism to do any of these steps will result in death. In the cases of intake and growth, death is of the individual while failure to reproduce results in death of the species.

Some species have several remarkably different stages to go through while growing before the species is mature enough to reproduce.  An example of this is the butterfly.  Others species, such as dogs, grow into adults from puppyhood, a stage in which the young animal already resembles the adult.

Frog spawn development, from Wikipedia.

All life forms go through these processes of intake, growth, and reproduction during their life cycle. In fact, they must go through these stages to preserve the species.

Let’s discuss how you can use your household pet to study life cycles, processes, and life changes. I have used a dog as an example here, but any pet can be studied in the same way.

Intake: A puppy needs nutrients to live and to grow. The required nutrients are food, water, and air. Each of these nutrients is needed for the chemical processes going on inside your pet. Actually, these are almost the same processes going on inside of you, too. Studying them with your pet should make your student more interested in those processes occurring in humans.

The first food for the puppy is, of course, mother’s milk, a food custom-designed by God for that species. Other mammals provide milk, too, but all milks are not alike. Some provide significantly more fat that others. The whale produces milk with the highest percentage of fat of any mammal, a fact which is useful to the baby whale while growing the fatty layer needed to survive in the cold oceans.

By the way, the first characteristic distinguishing mammals from other life forms is the production of milk for the young. Young animals of other phyla get their nutrients from other sources.   Reptiles usually do not care for their young, and so the young reptile will get nutrients from sources similar to those of the adult of the species. All of these topics are great ones to research during your science time periods.

Occasionally, a puppy has not been weaned before being separated from its mother. Perhaps the mother dog was killed and the puppy was not mature enough to be separated. Whatever the reason, a milk replacer is necessary. In the local pet store, you will find milk replacers for different species of pet mammal.

As an activity, you can visit the pet store and compare the different amounts of nutrients in each.  Build a chart showing the similarities and differences.

A prepared puppy food is designed to provide all of the nutrients that puppy needs for growth to maturity. Another good activity for your students is to check out the packages of puppy food in the grocery store. Your student should compare the amounts of everything in the grocery store puppy foods with those special puppy preparations found in the veterinarian’s office. You might also discover why they are more expensive. A comparison between adult dog foods and puppy foods is an excellent way to determine the special amounts of nutrients needed for growth.

Different mammals have radically different digestive systems.  

An excellent study would be to compare the digestive systems of dogs, cats, horses, and cows. This would include two herbivores and two carnivores.


Another way of looking at this small group of animals is by observing that their digestive systems are designed to get nutrients out of the food they eat. An animal which eats grass must have the ability to get through the cellulose layer of the leaf cell walls, so it can get to the nutrients.


How does a cow do this? How does the horse? Hint: The horse, like the rabbit and guinea pig, gets help from bacteria living in the caecum and/or colon.


Why does a cat, a carnivore, eat some types of grass? Hint: The word “compare” means to note both similarities and differences.

Your puppy will take in air from which his little lungs will extract oxygen. Many animals do not use lungs for this function.  Earthworms, for example, absorb oxygen straight through the outer layer, the skin. Fish use gills to extract oxygen from the water they swim in. By the way, this oxygen the fish breathe is from the oxygen which is dissolved in the water, not from the oxygen which is combined with the hydrogen to make the water molecules. You may have your student investigate gas exchange. This is the process of taking in oxygen and releasing carbon dioxide. Needless to say, all oxygen breathers do this, using different methods.

A puppy getting milk is also getting a good supply of water, another nutrient. As the puppy matures and is weaned, he will consume more water from his water bowl.

Water is a vital nutrient for your pet. All of the cells in the body depend upon a certain amount of water to maintain their functions.

A puppy needs an almost constant supply of water during the day. Of course, the puppy will also urinate more frequently than an adult dog necessitating vigilance on the part of the young puppy owner!

Growth: This is the process whereby an organism increases in maturity, strength, and usually size. During this process the young animal reaches his full adult size and also reproductive maturity.

The young of many species are built in a different proportion than is the adult of that species. Puppies have larger eyes, heads, feet, and tails in proportion to those of an adult dog. Then, later, the rest of the body catches up with these parts.

Artists, when drawing young animals, remember these proportions. A good activity is to collect pictures of young animals and older ones of the same type and compare their relative sizes of the parts of the body. You can do the same with a camera, recording your own pet’s growth.

Another activity is to keep a record of your pet’s height and weight. A line chart can be created using the data. This growth chart can be part of your student’s science lab notebook.

Reproduction: Nothing teaches the reproductive process like observing it happen. The birth of puppies is very exciting. Of course, the proper precautions must be taken because mother dogs can be extremely protective of their litters.

What are some of the things you can study about on the topic of reproduction?

Breeding and the different breeds of dogs is one topic. Dogs are a great example of diversity with the many sizes and colors, and other characteristics. It is hard to imagine that all of our modern dogs came from the same base stock of wild dog which probably looked very much like a mutt.   The reason for this is that the combinations of genes in a mutt are fairly well randomized again.  It makes the mutt sort of like turning back the selective breeding clock.

Another topic you can study is genetics.   Learning to do Punnet Squares is a good activity which even young children can do once they get some practice.

Having a pet can give you more than a year’s worth of biology to read about, talk over, and do.  Use the generalized life cycle to guide your research. Watch the blog this week for internet and print resources. Practice generalizing in your home school classes. In this way, you can combine owning a pet, teaching critical thinking, and studying biology.

Information to collect/record on your pet

Name of the animal:
Date of birth:
Date acquired:
Breed:
Phyla name:
Kind of animal:
Herbivore / carnivore / omnivore:
Brand / type of food:
Vet check date:
Immunizations and date:

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Cool Science Experiments- The Way to Get Your Kids Excited About Science

By Marianne Vanderkolk at Homeschool-articles.com

I love seeing kids excited about science.  Reading about science, exploring the world outside, seeing a science video are ways in which children enjoy and become motivated about science.  And, through the years, that is what we have successfully done. However, recently it has been confirmed in my own mind, that a real and extremely valid way for kids to love science and be keen to know more, is to provide them with time to play around with really cool science experiments.

As a homeschooling family we have questioned, “What have been the things that we look back on with fond and treasured memories in science?”   It is either the hands-on nature walks and finding animals, or the fun in setting up and doing an experiment with great results.  Many of the experiments my children have enjoyed have been totally unrelated to any science text we may have been following at the time.  Most of the successful ‘science’ messes have sprung up from their own interest and trying to solve a question which they have posed themselves. (Like fixing a cheap toy and making it far better than it ever was.)

So, how do we encourage our children to play around with science?

Ask Them Questions
Firstly, ask your children questions without giving away the answer.  If you are working through a text which has science experiments, present the question to them and don’t read or let them read what sorts of results they should be getting from performing the experiment.  Ask them questions during the experiment and after it – what do you think would happen if we changed  x, y or z?

Ask them questions about life – about their physical environment or why things happen?  Ask them the curious questions before they ask you.  And then let them think and ponder about it.  It does not mean that you should never give answers, but at the same time, don’t rush in – give them time first.  When answering, relate the answer to their current experience.  And remember, it is okay to admit you don’t know the answer – that can become an ideal time to discuss how to research and find answers we are looking for.

Let Them Experiment
Let them play with all sorts of things around the home and experiment.  Using a book or science course will give you ideas about exciting science experiments. There are also a ton of books at the library that will interest your children.  Recently, I discovered an online science Curriculum which is full of really cool science experiments.  You can see some here.

The experiment instructions are also on video, which we all really love watching. Using all sorts of common household materials, and some that you need to buy, these experiments have amazed and excited my children.  In fact, it has been the recent catalyst for a whole heap of hovercraft experiments which in turn has motivated my other children to fiddle with a toy gun changing it from a gun using air pressure to one using spring mechanics.

Be Prepared, Grow a Collection of Science Tools  and Encourage Mess
If you want your children to experiment, you will need to accept and even encourage mess.  Set up some boxes where you keep all sorts of odds and ends which will come in handy for science experiments.

  • You will need materials like rubber bands, straws, pipe cleaners, paper clips, balloons, popsicle sticks.
  • You will also need tools and materials to bind items together like sticky tape, masking tape, hot glue gun, super glue, rope or string, stapler and staples, hole punch, scissors.
  • Then you will also need to collect some clean junk – bottle tops, soda bottles, clean cans, bottle lids, ice cream containers and cardboard boxes of all sizes.

Perhaps you can create a science corner – filled with experiment books and all the materials, and a table to work on.

Allow for Mistakes
Every science experiment does not need to work perfectly and make sure your children know that.  When an experiment does not work the way they had hoped,  ask them:

  • “What did you learn from that?”
  • “What might you do differently next time?”
  • “Why do you think that happened?”

Be Curious Alongside of Them, But Don’t Take Over
When your children are in the middle of a project or have completed it, they love to have a fan club.  As they become more independent, they may not need you to set up an experiment or help them do it, but they really want to share their enthusiasm with an interested party – like their family and parents! So, let them inspire you – cheer them on as they set up an experiment – ask them questions so they can verbalize what is happening and why – problem solve with them – search out answers together,  BUT don’t take over.

As parents we have the tendency to ruin the child-led learning experience and make it a full-blown lesson.  We want to run with their idea because we can see how it will make a wonderful ‘unit study’ and so we plan, get books, blah,  blah, blah, and  run off with all of our great ideas, but meanwhile our children have turned the corner, lost interest  and moved on. It doesn’t matter!  Even if their interest in that topic may have been short lived, another experiment at a later date will most likely, help to reinforce the science concept.

So, do what you need to do to excite your children about science.

Be curious, ask questions, encourage messes, grow a collection of science tools and find materials to help you.  You can find some easy and totally ‘cool’ science experiments. as well as links to science experiments on video, plus two free Science Experiment Ebooks (A Science Experiment Guide usually valued at $25, and a Science Activity Manual and Video Guide valued at $30) , here – easy science experiments.