• Gloria Hoffner

Dogs Days of Summer

Hot days and seeking cool breezes are the way most would describe the month of August. However, ancient people had another way to describe this time of year, the dog days of summer. When asked, most 21st century responders often say, “It’s the dog days because it’s so hot dogs are panting.” Fun answer, but not true.

Dog Days is a term created by the ancient Romans who understood and mapped over 1,000 stars in the night sky. Every day Romans needed this knowledge as it helped them navigate when traveling. To these people, dog days referred to the star Sirius, the dog star. It is the brightest star in the constellation Canis Major, which translated means Large Dog.

Because Sirius is the brightest star in the night sky, the Romans believed it radiated extra heat to the Earth. Sirius rises and sets with the sun during the summer months and thus they believed it created hotter temperatures on the Earth.

Under the Roman calendar, dog days began about July 24 and lasted until August 24th. Today the traditional period of the dog days is from July 3 to August 11 in the Northern Hemisphere. In the Southern Hemisphere the dog days are from late January until early March. The variation in dates is due to the latitude and the climate in each location.

The Romans were wrong about the Sirius creating more summer heat. Our seasons are due to the tilt of the Earth, about 23.5 degrees, as it circles the Sun. During summer months light from the Sun hits our planet at a more direct angle and for a longer period of time during the day resulting in longer and hotter days.

Experiment Project Canis Major and Sirius on the Wall


· Empty round oatmeal container

· Scissors

· Sharpened pencil

· LED flashlight

· Cardboard

· Dark room

Setting up process & experiment:

1. Cut out the cardboard from inside the plastic circle, but do not remove the plastic circle, on both ends of the oatmeal container.

2. Draw an image of Canis Major on one of the removed cardboard circles.

3. Use the pencil point to poke holes through the cardboard at the location of the Canis Major image stars.

4. Put the cardboard with the Canis Major stars and poked holes back into the plastic edge of the oatmeal container.

5. Place the LED flashlight in the open end of the oatmeal container.

6. In a dark room, hold the oatmeal container facing a wall, turn on the flashlight and watch the filtered light form a projection of the Canis Major constellation.

More observations:

· Repeat the projection in a lighted room.

· Repeat the projection outdoors in sunlight.

What is the science? What did we learn? Why did it happen?

When you shine the flashlight through the pinholes of the cardboard design of Canis Major the light travels in a straight line and projects the image of the constellation on the dark wall.

When you project the image outdoors in sunlight you can not see the image of Canis Major. This is for the same reason you can not see the stars in the sky during the day. The stars are there however the Earth’s atmosphere scatters the light from the sun and thus make individual stars impossible to see in daylight hours.

A flashlight creates photons so you see the light from the flashlight in a dark room. However, in a bright room there are already lots of photons so your eyes can’t distinguish the light generated by the flashlight.

Change a variable

· There are many stars in the sky and popular constellations. Have residents make their own cardboard image and take turns showing them on the wall. This website has free printable images:

· Here are some examples:


1. What is a star? Answer - A star is a mass of hydrogen and helium with a nuclear fusion in the core.

2. How do stars form? Answer – Stars form from a cloud of interstellar dust and gas that collapses on itself which heats up causing the nuclear fusion of hydrogen into helium.

3. How long does it take for a star to form? Answer – The process starts with a protostar, which is when the gases collapse into a large molecular cloud. This lasts for about 100,000 years before heat begins which will start the nuclear fusion. For our sun, the process from gas to star was about a million years.

4. Why are stars different colors? Answer – The color of the star depends on the surface temperature of the star. The hottest stars are blue and the coolest stars are red.

5. What are examples of different stars? Answer – A Type M star is red and has a temperature between 3,000- and 6,000-degrees Fahrenheit. A Type K star is orange and has a temperature between 6,000- and 8,500-degrees Fahrenheit. A Type A star is white and has a temperature between 13,000- and 17,500-degrees Fahrenheit. A Type O star is blue and has a temperature between 50,000 to 100,00 degrees Fahrenheit.

6. What kind of star is our sun? Answer – Our sun is a yellow white dwarf Type GV2 which means it is 2/10ths of the stage towards becoming a Type F with a temperature of between 10,500- and 13,000-degrees Fahrenheit. Our sun today has temperature of between 5,200- and 6,000-degrees Fahrenheit.

7. What type of star is Sirius? Answer – Sirius is actually a binary star made up of both a Type A which is larger and brighter than our sun and a white dwarf star which is smaller than our sun and the remains of remains of a dead star.

8. When did astronomers discover it was two stars orbiting each other? Answer – Sirius A is the brightest star in the sky and can be seen by the naked eye since earliest records. In 1862 astronomers using a telescope discovered the smaller companion dwarf star named Sirius B.

9. How does Sirius compare to our sun? Answer – Sirius A is two times larger than our sun and 20 times brighter. Sirius B is 10,000 times dimmer than Sirius A.

10. How long would it take to travel to Sirius? Answer – Based on the speed of satellites orbiting the Earth at 5 miles per second, if you build a space ship with the same speed it would take you about 334,800 years to reach Sirius.

11. Are there planets orbiting Sirius? Answer – None have been found, yet. Astronomers search for new planets with improved telescopes daily. They speculate that if we find planets orbiting Sirius they would be covered in thick atmosphere, have shallow oceans, little land mass and be subjected to sterilizing ultraviolet light from Sirius.

12. What is a constellation? Answer – A constellation is a group of stars that to ancient humans appeared as a familiar image such as a person or animal.

13. Why did humans invent constellations? Answer – On a clear night in total dark skies, you can see over 1,000 stars in the sky. Historians believe that earliest people created constellations, which vary in name and design by culture, as a way to recognize changes in the night sky.

14. Who created astrology with the constellations? Answer – The Babylonians in 1600 BC created what we know as Zodiac constellations. They believed the placement of the stars predicted future events. This has been proven false many times.

15. Why is the Zodiac false? Answer – The Zodiac is based on the path of the sun thus ancient people believed the position of the sun in connection with the constellations on the day you were born was your sign. These ancient people did not know that precession, the wobble of the Earth due to the tug of the Moon’s gravity, is a 25,800-year cycle. This means, the ancient constellation positions are off by about a month. For example, if you think you are an Aries, the real position of the sun at your birth is Pisces.

16. Will Sirius always look the same? Answer – No. Gravity in the galaxy is moving all the stars. In about 60,000 years Sirius will be closer to our solar system and appear even brighter. Then it’s orbit will start to move it away from Earth and will gradually become dimmer. However, it will remain the brightest star in our night sky for about 210,000 years.

For additional science experiments visit

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