My Science School

 

What are circumpolar stars?

Circumpolar stars (also called non-setting stars) are permanently neither visible above the horizon rise nor set. The number and type of circumpolar stars will naturally depend on the location of the observer. At the Equator, the northern and southern celestial poles would appear on the horizon, and no stars would be circumpolar. For intermediate latitudes, some stars would be circumpolar, some would rise or set and some would never be seen at all.

 

 

How do astronomers locate and refer to individual stars in the sky?

The coordinates that determine the position of a star on the celestial sphere are “Right Ascension” (R.A) and “Declination” (D.). These are polar coordinates which specify of reference of the star and determine the celestial longitude and latitude at which the star can be located.

What is Right Ascension?

The Right Ascension reference gives the celestial longitude of a body Zero Right Ascension reference is the point where the celestial equator and the ecliptic intersect. In other words, it is the vernal equinox or the point at which the Sun moves into the northern half of the celestial sphere. Considering that one circuit of the celestial sphere is equivalent to 3600 in 24 hours, we can say that 150 of Right Ascension are equivalent to 1 hour of time. The meridians at intervals at 150 are therefore called Hour Circles for the same reason. The Right Ascension reference helps the observer to align himself in the correct direction on the horizontal plane.

What is Declination?

Once the observer has aligned himself in the correct direction on the horizontal plane through the Right Ascension reference, he can locate the star by aligning himself along the vertical plane. In other words, together with Right Ascension, Declination defines the position of a body in the sky. Declination is the extent to which the star is above the celestial equator. Declination can therefore vary from 0 to 900.

 

 

 

What is correction for planetary parallax?

The coordinates (R.A. & D.) of astronomical bodies on the Celestial Sphere are theoretically with reference to the centre of the Earth. The observations of an observer located on the Earth’s surface have necessarily to be corrected by the distance between the Earth’s centre, is called correction for planetary parallax.

 

 

 

What is the ecliptic of the celestial sphere?

The ecliptic of the celestial sphere is the counterpart of the ecliptic of the earth’s sphere. Since the Earth’s ecliptic is inclined to the Earth’s Equator by 23.50 the ecliptic of the celestial sphere is also inclined by 23.50. Generally, when we say “the Ecliptic” we mean the ecliptic of the celestial sphere otherwise specified.

The ecliptic is therefore a circumferential line or great circle on the celestial sphere, titled to the celestial equator at an angle of 23.50.

What are the North Pole of Ecliptic and the South Pole of Ecliptic?

Just as the ecliptic can be visualized as the celestial equator displaced on the celestial sphere by 23.50, we can visualize the north and south celestial poles to be correspondingly displaced by 23.50 on the celestial sphere to form respectively the North Pole of Ecliptic and the South Pole of Ecliptic.

 

What is the significance of the ecliptic, the equinoxes and the solstices?

These parameters have been closely related to the changes of seasons on Earth since ancient times.

What are the equinoxes?

The two times in each year when day and night are of equal duration are called equinoxes. The ecliptic intersects the celestial equator at two points, called the points of summer or vernal equinox or “Vasanta Sampaat” (which occurs on 21st March) and the autumnal equinox or “Sharad Sampaat” (which occurs on 22nd September respectively.

What are the solstices?

The points midway between the equinoxes are called the points of summer solstice (which occurs on 21st June) and the winter solstice (which occurs on 22nd December).

 

 

 

Continue reading "The Night Sky"

 

 

Does the Pole Star have any practical significance?

The Pole Star (Polaris or ‘Dhruva’) helps navigation locate the north direction in the absence of any landmark, even in deserts and oceans. This is also called the “North Star”.

 

 

 

 

 

 

 

 

 

What are the pointer stars or “The Pointers”?

The stars Alpha and Beta (Dubhe and Marak) in the constellation Ursa Major (also known as Great Near, Big Dipper, Plough or “Saptarishi”) are called “The Pointers” since a line drawn through these stars points towards the Pole Star.

Is there any star like Polaris at the South Celestial Pole?

No. However, a group of star known as “Crux” (“Trishanku” or “Southern Cross”) is situated almost at the South Celestial Pole and helps navigators in locating the south direction.

 

 

 

 

 

Continue reading "The Night Sky"

 

 

Why don’t the Sun and Moon twinkle?

Though the Earth’s atmosphere distorts the light in all cases, the twinkling phenomenon is noticeable only when the object appears very small in the sky. Even planets and large stars may appear to twinkle only when they are near the horizon. The Sun and the Moon are obviously too large for the twinkling effect to be noticeable.

 

 

 

 

 

Does nearness of a celestial body to the horizon have any effect other than increasing the twinkling?

Yes. The colour of the object turns pink, a reason why the Sun appears red during sunrise or sunset. Mercury also sometimes appears pink when seen near the horizon.

 

 

 

 

 

 

 

 

What is meant by the apparent and true direction of the Sun?

The true direction of the Sun is always different from the apparent one due to refraction of Sun’s radiation in the Earth’s atmosphere.

 

 

 

 

 

 

 

What is the Celestial Sphere?

It is imaginary sphere with the Earth as its centre and having a very large radius. The position of bodies such as stars, planets and galaxies are specified by their coordinates on the celestial sphere. In ancient times, the astrologers considered the Earth to be surrounded by the Celestial Sphere were attached to it.

Does the celestial sphere concept have any significance in modern astronomy?

No. The Earth hides part of the celestial sphere below the horizon.

What are the celestial poles, the celestial equator and celestial meridians?

The celestial sphere is assumed to posses’ poles, equator and meridians like the Earth. The point on the celestial sphere directly above the Earth’s geographical North Pole is assumed to be the north celestial pole. Similarly, the point on the celestial sphere directly above the Earth’s geographical South Pole is assumed to be the south celestial pole.

What is the celestial equator?

The celestial equator is the imaginary line representing the circumference of the celestial sphere and situated midway between the celestial poles.

What is the significance of the celestial poles?

When the Earth rotates on its axis, the celestial sphere also appears to rotate around its axis. A star situated at a celestial pole directly above any of the Earth’s poles would appears not have any lateral movement while the Earth is rotating.

 

 

What is the horizon?

The horizon is the limit of the observer’s field of vision from any point on the Earth’s surface. It is the maximum distance to which one can see across the horizon appears as a distant circular boundary surrounding the observer. The horizon recedes as one goes higher above the surface of the Earth i.e. the field of view increases.

 

 

 

 

 

How do meteors shine?

Meteors shine when they heat up and burn due to air friction while falling through the Earth’s atmosphere.

 

 

 

 

 

 

How do comets shine?

When a comet approaches the Sun, the heat from the Sun vaporizes part of the material in the comet, causing it to glow.

 

 

 

 

 

Why do stars twinkle?

Distortion of star light by Earth’s atmosphere makes the stars apparently twinkle.

Do stars twinkle uniformly in all parts of the night sky?

No. Stars twinkle more when they are near the horizon, since their light has to pass obliquely through a thicker layer of the Earth’s atmosphere which has a greater distortion effect.

 

How does the Moon shine?

The moon does not generate light of its own but reflects the light emitted by the Sun. It’s apparent large size causes it to appear brighter compared to other objects that are brighter but farther away from the earth.

Name the brightest object in the sky after the Sun.

The Moon.

Why is the clear night sky important to astronomers?

It allows visibility of almost all celestial bodies unhindered by the Sun’s glare.

 

 

 

 

 

 

 

Continue reading "The Night Sky"

 

What are the Solstices?

During the year, the position of the Sun in the sky, as viewed from the Earth shifts from north to south and back again. In other words solstice occurs on either to the days on which the Sun is farthest north or south of the celestial equator each year. The points of solstice correspond to the northernmost and southernmost positions of the Sun in the sky.

 

 

 

What is the structure of the Earth?

Earth has a molten liquid core of iron, nickel and magnesium silicates. At the surface of the Earth is a solid layer called the crust. A semi fluid zone called the mantle exists between the crust and core. About 70% of the Earth’s surface includes north and south polar icecaps it is covered with water.

 

 

 

 

 

 

 

 

What is the precession of the Earth’s axis?

The Earth’s axis does not remain steady but wobbles like that of a tilted spinning top. This wobbling is called the precession of the Earth’s axis.

 

What causes the change in seasons on Earth?

In the northern hemisphere, the Earth’s 23.50 tilt towards and away from the Sun during June and January causes’ summer and winter respectively. It would be the converse in the converse in the southern hemisphere.

Does the change in the Earth-Sun distance during an year have any appreciable effect upon the seasons on Earth?

No.

 

 

Do the hemispheres have identical temperatures during summer and winter?

Theoretically, the Earth should have a slightly hotter climate in the southern hemisphere compared to the northern hemisphere. However, the larger mass of ocean in the southern since the ocean heats up and to even down more slowly than land areas.

 

 

 

Continue reading "The Earth"

Port Blair                           -41          

Guwahti                          -37

Patna                             -11

Lucknow                        +6

Delhi                             +21

Srinagar                       +31   

Panaji                           +35        

 

Port Blair                           -41          

Guwahti                          -37

Patna                             -11

Lucknow                        +6

Delhi                             +21

Srinagar                       +31   

Panaji                           +35        

 

 

 

 

What is a civil day?

A civil day is the day of 24 hours used routinely on Earth for setting clocks i.e., 24 hours divided into two portions- day time and night time- depending on whether the Sun Shines in the sky or not.

 

 

 

 

 

 

Does the difference between the civil and astronomical days have any significance in astronomical observations?

 

 

Since the civil day is 3 minutes and 56 seconds longer than the astronomical day, any star in the sky will rise 3 minutes and 56 seconds earlier every day compared to the previous day.

 

What is the time difference between a lunar and a solar year?

A solar year has 365 days. A lunar year has 354 days, and is based on twelve complete moon phase cycles or lunation.

Are all calendars based on the solar year?

No. Some calendars (such as those of the Mohammed am era) are based on the lunar year.

 

 

 

What is an astronomical year?

An astronomical year (also known as sidereal year) for a planet is the time taken by the planet to make a complete revolution around the Sun. In the case of the Earth, the sidereal year is equal to 365.2564 mean solar days or 365 days 6 hours 9 minutes and 9.5 seconds.

 

 

 

 

What are the regions or zones of the Earth?

The regions north of the Arctic Circle and south of the Antarctic Circle are called the Polar Regions or frigid zones.

The region between the Tropic of Cancer and the Tropic of Capricorn is called the Torrid Zone. The regions between the Tropic of Cancer and the Arctic Circle and between the Tropic Capricorn and the Antarctic Circle are called the north and south temperate zones respectively.

 

 

 

 

 

 

What are the polar ice caps?

Extremely cold temperatures of the Polar Regions cause ice formation on land and sea, resulting in a permanent blanket of ice around the poles called the polar ice caps.

 

Continue reading "The Earth"

 

Can all spherical celestial bodies be imagined to have their own equator, poles, latitudes and longitudes?

Yes, all spherical celestial bodies are imagined to have their own equator, poles, latitudes and longitudes.

 

 

 

What are the tropics?

The latitude 23.50 North of the Earth’s equator is called the tropic of cancer.

The tropic of Capricorn is the latitude 23.50 south of the Earth’s equator. There are limits of the area of earth’s surface in which the Sun can be directly overhead.

The peak activity was, however, visible only in the north Pacific region.

 

Continue reading "The Earth"

 

 

What are latitudes?

Latitudes are imaginary lines between the equator and the poles which run parallel to the equator and divide the surface of the Earth into parallel segments. Latitudes are also called “Parallels” or “Parallels of Latitude” e.g. 20 degrees latitude.

 

 

 

 

What are longitudes?

Longitudes are imaginary-lines through the geographic poles which run circumferentially and intersect the surface of the Earth dividing it into segments e.g.  20 degree w longitudes. (For example, if the Earth is imagined as an orange, the longitudes would divide it into its natural “slices”). Longitudes are also called “Meridians” or “Meridians of longitude”. The  zero degree meridians is also called the “Greenwich” meridian since it passes through the town of Greenwich in England.