Some Clarifications of ASTRONOMICAL scale

Hello friends,

I have been replying some queries and some "updates" from my friends, about particularly 2 "once in a lifetime" kind of astronomical phenomenons which would be sighted by our "Lucky" generation.

Yes I am talking about the two hoax mails that talk about

• Mars being closest to earth and being the size of the moon in sky,
• Some stupid asteroid coming 35.5 million miles close to earth and being as bright as SUN

So my reply to every question was with an exclamation and then a 15-20 min casual lecture describing our solar system, and the facts about why planets seem to be the size and brightness in the sky.

So lets go step by step in reasoning this.

• When it comes to Mars, the average distance from earth varies between 0.6A.U. to 2.6 AU. 1 AU is the mean distance between earth and sun standardised to be approximately 150 million kilometers. Now this fluctuation of distances is due to differences in time taken by each planet to complete one revolution around sun. This asynchronous movement creates two specific cases called as opposition and conjunction. (see Diagram).

• Opposition is the state when the planet and the sun are on the opposite sides of earth. This is the point when the planet can be the closest and brightest. Now in case of Mars this happens roughly every 1.8 years.. Reason : Earth is 1.8 times quicker around the sun than Mars.Now this shows that Mars being close to earth is not at all an uncommon fact. But the distance when Mars is in opposition really varies.

• Now comes the question of how close can it really come. The answer is that the closest ever recorded distance is roughly 56 Million Kilometers or roughly 0.35 AU. Now why is this discrepancy? Reason is simple: Earth and Mars orbits are eccentric. Hence even the distance between the orbits vary. For a better understanding of earth and mars dance around sun go to this link.
• The closest possible position would be seen on date near to 31st Aug 2003. This was when mars was closest ever. Now this is what is really once in a lifetime kind of situation. But again... even if this is a rare event , it is not as spectacular as the mail says. I have seen it, mars does look bright but not as big as the moon. Again lets reason it out.
• Moon is roughly 300 thousand kilometres away and its size is roughly half a degree or 0.5 degrees. Now if I give you distance of moon from earth and diameter in kilometers, you can easily find its angular size using simple trigonometry. Using the same logic if I give you distance of Mars as 56000000 km (closest ever) and size as 6800 km (diameter of mars) what you get is 0.007 degrees which is 70 times smaller than moon. You can try it out yourself by using this link. Evaluate for Angle. Put distance as 56 million and size as 6800 see wat you get. Then put distance as 300 thousand and size 3500 km (moon dia) and compare what you get :).

So now that the Mars hoax is solved... we can use the above procedure to calculate the size of an asteroid that comes 35 million km close (hardly possible number as it breaches danger levels and we would know about it atleast a decade before). Largest asteroid known till now is CERES which is about 1000 km on its biggest axis. Put this size and distance as 35 million in above link and see what you get. Sun's angular size is also around 0.6 degrees {thats why moon can eclipse Sun :) } and Ceres is now way close to it.

I hope my blog was simple to understand. Do give me a feedback. Lets be aware of our universe and stop such hoaxes from spreading. I will post some fun facts about universe shortly. Keep reading :) .

Sagar