Science Chapter 17 Flashcards
During solar eclipse ………….. comes between the sun and earth.
Moon
A solar eclipse is seen only on a ………….. day.
New moon day
During lunar eclipse ……………. comes between the sun and the moon.
Earth
A lunar eclipse is seen only on a ………….. night.
Full moon
The day on which the sun reaches exactly overhead is called the …………… .
Zero shadow day
As seen from the earth, when a planet or star passes behind the moon, that state is called a ………….. .
Occultation
Why does the sky appears blue to us?
The sky appears blue because sunlight is scattered by gases like nitrogen and oxygen. Blue light, having a shorter wavelength, is scattered more than other colors.
Why is the solar eclipse either partial or total?
A solar eclipse is total when the moon completely covers the sun. If the moon covers only part of the sun, it is a partial solar eclipse.
Explain the difference between solar an lunar eclipse
Solar Eclipse
1.When the moon comes between the sun and the earth, a shadow of the moon is cast on the sarth
2.A solar eclipse is seen only on a new moon day.
3.A solar eclipse should never be watched with the naked eye. because ultra violate rays which are harmful to us reach the earth
4.It can be seen for a few minutes only.
Lunar Eclipse
1.When the earth comes between the sun and the moon a shadow of the earth is cast on the moon and a part of the moon in covered this is called the lunar eclipse.
2.A lunar eclipse is seen only on a full moon night.
3.A lunar eclipse can be seen with the naked eye.
4.It can be seen over a period of a few hours.
Explain solar eclipse with diagram
During its revolution, when the moon comes between the sun and the earth, a shadow of the moon is cast on the earth and the sun cannot be seen from the part in the shadow. This is called a solar eclipse
A solar eclipse is seen only on a new moon day.
The solar eclipse may be either partial or total,
Sometimes the solar disc is completely covered by the moon. This is the total solar eclipse.
When the solar disc is not covered fully by the moon, we have a partial solar eclipse.
During a solar eclipse, ultra-violet rays which are harmful to us reach the earth.
A solar eclipse should never be watched with the naked eye.
A special type of goggles should be used for this purpose.
Solar eclipse can be seen for a few minutes only.
Diagram :- Solar Eclipse
Explain lunar eclipse with a diagram.
When the earth comes between the sun and the moon a shadow of the earth is cast on the moon and a part of the moon is covered. This is called the lunar eclipse.
A lunar eclipse is seen only on a full moon night. If the whole moon comes in the shadow of the earth, it is a total lunar eclipse.
When the shadow of the earth is cast only on a part of the moon, it is a partial lunar eclipse. You can watch a lunar eclipse with the naked eye.
A lunar eclipse can be seen over a period of a few hours.
Diagram: -Lunar eclipse
Write short note on zero shadow day
The day on which the sun reaches exactly overhead is called zero shadow day.
On this day, at noon, shadow completely disappears.
This event can be seen in the region between the Tropic of Cancer (23.5°N) and at tropic of Capricon (23.5°S).
The shadow diminishes and eventually disappears for a while only to reappear later
This phenomenon occurs twice every year Mumbai got to witness it on May 14, 2018 last year.
Write a short note on shadow.
Shadow is a dark patch formed behind an opaque object when it is placed in the path of light.
A shadow is formed only when a light source, an opaque object and a screen are present, e.g. during a lunar eclipse we see a part of the earth’s shadow on the surface of the moon.
This happens when the earth, the sun, and the moon are in a straight line with the earth between sun and the moon.
Here the sun acts as the light source, the earth as the opaque object and moon as the screen.
Shadows are formed due the rectilinear propagation of light.
The size and the shape of the shadow depend on the position and orientation of the opaque object between the source of light and the screen.
If the distance of the object from the source is decreased, then the size of the shadow increases.
If the object is moved away from the source, then the size of the shadow decreases.
In older days shadows caused by objects placed in the sun were used to measure time. Such a device is called sun dial.
Eclipses and transits which will occur recently.
January 6, 2019 – Partial solar eclipse
January 21, 2019 – Total Lunar eclipse
July 2, 2019 – Total solar eclipse
July 16, 2019 – Partial Lunar eclipse
December 26, 2019 – Annular solar eclipse.
What is an occultation?
As seen from the earth, when a planet or a star passes behind the moon, that state is called an Occultation.
