All of you have possibly seen a total solar eclipse some time or other. Have you ever wondered at the strange coincidence that makes this spectacular event possible? Even a schoolboy knows that the disk of the Moon comes between the Earth and the Sun to block our view of the Sun, resulting in the solar eclipse.
But have you ever thought that this celestial spectacle, which has interested men for thousands of years, has been possible due to a strange coincidence? The diameters of the Sun and our Moon happen to be almost in the same ratio as their distances from the Earth (approximately 1:400). As a result, the apparent sizes of the Moon and the Sun look same and the lunar disk can just about cover up the solar disk – giving us the total solar eclipse! In a total eclipse, only the Sun’s corona remain visible. Had those distances or the sizes been different from actual, what would you expect to see? Either the Moon would look so big as to cover up the Sun as well as some part of the corona, or it would look so small that it would be unable to cover the full face of the Sun. Either way, nothing like a total solar eclipse would ever occur.
Since ages, we have been told that our Solar system has 9 planets orbiting the Sun. But this number now stands at 8 after 2006 when Pluto was stripped of its rank! Pluto is now classified under a new category of celestial bodies – called Dwarf Planets. It shares this designation along with 4 others – Ceres, Haumea, Makemake, and Eris. Ceres is in the Asteroid belt between orbits of Mars and Jupiter, others are beyond the orbit of Pluto in the order named.
One family that has been growing without control is that of the moons and as in October last year, the family size was 172 and more may get added in future! Though Mercury and Venus are planets, they have nothing to show when the Dwarf Planets among them boast of six! Shame! Mars has 2, Jupiter 63, Satiurn 60, Uranus 27 and Neptune has 13. Luckily we have one and who wants more? About one-third people in the world follow lunar calendar and imagine the kind of confusion they would suffer if there were half a dozen moons flying around our Earth!
We may have only one, but our Moon ranks 5th in size in this crowd, coming after Jupiter’s Gannymede, Saturn’s Titan and two more of Jupiter namely Callisto and Io, in that order. Not bad for a lilliput like our planet when you consider that Jupiter and Saturn are respectively 11 times and 9 times as big as Earth. Quality before quantity, that is our baby!
When you look at the sky on a clear night,you feel that the number of visible stars are uncountable. But are they really? Actually, at any point of time, we can see only about 2500 with our naked eyes. Not a very large number, is it?
Brightness of celestial objects is designated by a magnitude rating from negative numbers for very bright objects to positive numbers denoting progressively dimmer ones. The larger the number, the lower is the apparent brightness. Mind that the brightness in absolute terms may be quite different because the distance affects the brightness as seen by us.
The unit of magnitude is taken as the brightness of a candle seen from a distance of 1300 feet. The star Vega is a 0 magnitude star (apparent magnitude .03), Antares is first magnitude (1.2), Polaris or North Star is second magnitude and so on. The sixth magnitude stars are the dimmest that we can see with naked eyes. The first magnitude star is approximately 2.5 times as bright as a second magnitude star which is about 2.5 times brighter than a third magnitude star and so on. Thus a fist magnitude star will be 100 times brighter than a sixth magnitude star.
The brightest star in the sky is Sirius which has a magnitude of -1.6. Venus (though only a planet, it is often described as a Morning Star or Evening Star depending on the time of the year) has a magnitude of -5, Full Moon -12 and Sun -27.
All of you know that our Sun is a star and a medium sized one by heavenly standards. Which are the giants in the star family? Antares and Betelgeuse, to name two in this category. Betelgeuse can be readily identified as the star which forms the right shoulder of Orion, a constellation easily made out in the night sky. If one of these stars were placed where our Sun is, all planets upto Mars would fall into the star as the star boundary would go beyond the orbit of Mars! Lucky we are, aren’t we?