Category

Star watching in the daytime

Introduction

Watch stars in the daytime

　The rotation of the Earth on its axis results in the objects in the sky appearing to rise and set each day and this motion is called diurnal or daily motion.You usually have to go outside at night and watch stars. We can regularly see stars shining in the dark night sky, and this is not unusual. So, there are no stars in the daytime sky, are there? Yes, there are stars in the daytime, too.
　Then, let's watch some movies of stars in the daytime which were taken by Miyagi University of Education internet telescope and see what stars look like in the daytime. Try to think of the mechanism of the daily motion and think why we can not easily see stars in the daytime

Understanding the Celestial Sphere

　To help understand the motion of the stars, an imaginary ceiling "The Celestial Sphere" is useful. About the Celestial Sphere
The sun is also one of the stars, so it can be attached to the surface of the celestial sphere. Put the sun onto the celestial sphere in the figure below that shows the position of the sun and earth on summer solstice.
The Earth's axis does not point directly toward ecliptic north. It points 23.4 degree from ecliptic north toward the summer solstice. That is, the Sun is 66.6 degree from the earth's axis, so it can be attached as in the next figure.

　Rotating the figure to make the ground which the red person on the Northern Hemisphere is standing on horizontal will produce the figure shown below.
Here is the question! Is it the night sky or the daytime sky that the red person standing at the centre is watching?

The answer is..

Pictures/ Movies

　The answer is "Daytime sky". Because, the sun is in the sky.
There are also some stars as well as the sun. Yes. The stars are there even in the daytime!
　Watch the stars in the daytime in the pictures or movies below. The white spot in the centre is the star.

The stars in the daytime A background star is a star far away which provides its own light. You can see it like a shiny spot.
Sirius （October 9, 2003 at Miyagi University of Education Observatory） It is a star in Great Dog, winter constellation. It is the brightest star in the sky apart from the sun. Larger
Albireo （September 23, 2003 at Miyagi University of Education Observatory） It is a star in Cygnus, summer constellation. It is a very popular star that consists of two different coloured stars. You can not tell the difference of the colours in this picture, still can see two stars and know it is a double star. Larger Movie
Vega （October 7, 2003 at Miyagi University of Education Observatory） It is a star in Lyra, summer constellation. It is one of the summer triangle. Larger Movie
Arcturus (October 7, 2003 at Miyagi University of Education Observatory） It is a star in Bootes, spring constellation. It is one of the spring triangle. Larger
Altair (September 23, 2003 at Miyagi University of Education Observatory） It is a star in Aquila, summer constellation. It is one of the summer triangle. Larger
Planets in the daytime Venus and Jupiter are planets in the solar system. They are not as distant as the background stars. They only reflect the Sun's light. They can be seen larger.
Venus (October 6, 2003 at Miyagi University of Education Observatory） It is the second planet from the Sun.（The earth is the third.）The size and the density are very similar to the earth. It waxes and wanes like the moon because its orbit lies inside the orbit of the earth. Larger Venus Live: Observing Log
Jupiter (September 30, 2003 at Miyagi University of Education Observatory） It is the fifth planet from the Sun.（The earth is the third.）It is the largest, heaviest planet in the solar system. It is made of gases such as hydrogen and helium unlike the earth. Larger Movie

Discussion

• Why can we not easily watch stars in the daytime?
  
• Can we see the same star in the same place in the night, which we watched in the daytime?

Venus Live

金星ライブページ