Merlin is as old as Earth and has been an eyewitness to nearly all major human discoveries in the physical sciences. On temporary leave from home--the planet Omniscia in the Draziw star system of the Andromeda galaxy--Merlin has chosen Earth and its scientific legacy as a topic of academic research. Merlin has advanced degrees in astrophysics, geophysics, chemistry, and philosophy, all earned at Omniscia's planetwide Universe-ity.
A consummate scholar-educator, Merlin loves nothing more than to answer your questions about our favorite universe. Steadfastly succinct yet always friendly, Merlin's replies are occasionally enriched by recollections from the past--a past that contains a motley assortment of Merlin's Earth-based friends and acquaintances, including Archimedes, Galileo, Einstein, and Santa.Dear Merlin,
With all the motion of Earth through space, when I jump, how come I don't land in a different place?
You do land in a different place in space, but the ground stays with you. If you jump straight up and manage to stay airborne for one second, then you will land over 500 yards east (the rotation of Earth carried you there) and 18 miles farther around the Sun (the orbit of Earth carried you there) and about 125 miles farther around the center of the Milky Way galaxy (the orbit of the solar system took you there). Incidentally, all this happens in one second even if you do not jump. Dear Merlin,
What is a blue moon?
LINDA HAYDEN, MOONMAIDEN
ARCADIA, SOUTH CAROLINA
In the absence of blue-tinted moon glasses or peculiar atmospheric optics, a blue moon is simply the second full moon in a calendar month. With months of twenty-eight, twenty-nine, thirty, and thirty-one days and the average cycle of full moons requiring twenty-nine and a half days, the average time between blue moons is about two and a half years. Occasionally, however, blue moon enthusiasts get a treat. In 1999, 2018, and again in 2037, January has two full moons. In each year, February follows with no full moon, but then March dons two full moons of its own.Dear Merlin,
Our planet is becoming overburdened with atomic waste and hazardous materials at an alarming rate. Why can't we put some of it on space flights when room is available and have the astronauts nudge the stuff in the direction of the Sun?
LESTER DUBACH HELLMAN
PRESCOTT VALLEY, ARIZONA
What you call a "nudge" from an already orbiting space station amounts to shoving the atomic waste in the right direction at a speed of about 7,000 miles per hour. Only then will it escape the gravitational pull of Earth. If the high-speed nudge fails, the waste will reenter Earth's atmosphere and create an even greater health risk. The solution for your planet is to find sources of energy that do not produce atomic and otherwise hazardous wastes. Dear Merlin,
At about 10:30 p.m. this past July 31, my mom and I saw a small reddish light move quickly across the sky. It tracked through the Big Dipper. It did not blink, like a plane's light might. It was gone from our sight after fifteen seconds or so. Do you think it was a satellite? If so, what kind? And where are they going? How can we see more of them?
CARA AND KERRY
DUBYK FURLONG, PENNSYLVANIA
Since your mother also saw the light, Merlin presumes you were not hallucinating. You probably saw an artificial satellite in low Earth orbit with a polar trajectory. During the several hours after sunset and before sunrise, if a satellite happens to fly over your town, it will be visible because of reflected sunlight before it enters (or after it exits) Earth's cone-shaped shadow in space.
Polar trajectories are ideal for spy satellites because they orbit from pole to pole while Earth turns continuously, which eventually allows the satellite to see every part of Earth's surface, including you and your mother. Next time, wave. Dear Merlin,
My question relates to time. I am told that time began at the beginning of the universe, but if time had a beginning, then what was "time" before it began? And if time were to end, wouldn't there still be "time" after it ended?
PAUL W. QUANDT
Where there are no repeating phenomena, the measurement of time, and time as we know it, cannot be defined. The interval that separates two events is commonly measured by something that repeats--the vibrating crystals of a modern digital watch, the pendulum and gears of a grandfather clock, the rising and setting Sun, heartbeats, etc. We presume that outside the universe (this includes before the beginning and after the end), there are no events and, of course, no measuring devices. In such a place, time would have no meaning. In practical terms, time would be irrelevant. But do not let this upset you. There are many systems where time is mostly irrelevant, and you needn't leave the universe to find them. All those who use mathematics to describe the physical universe will use time in their equations only when something changes in their system. Otherwise, the system is in "steady state," and time is handily excised from the computations. For example, the structural engineers who design today's suspension bridges have few occasions to use time in their equations. A bridge is the graceful conquest of balanced forces. Were it not for corrosion, continental drift, and the Sun becoming a red giant, a bridge would last forever--in timeless, blissful, and steady state. Dear Merlin,
How will the universe end?
S. KENT WALLACE
GRAND RAPIDS, MICHIGAN
Merlin asked that question of the British author T.S. Eliot in 1925. He replied with poetic clairvoyance: This is the way the way the world ends
Not with a bang but a whimper.
Latest evidence suggests that there is not enough mass and gravity to halt or reverse the expansion of the universe. In this scenario, star formation ultimately consumes nearly all interstellar gas. The remaining stars exhaust all their fuel as the universe expands forever and cools to a dark, frigid, thermodynamic death. After about 10 years (10 sextillion times the current age of the universe), even the proton, the very fabric of matter itself, will decay. Such a fate may sound unpleasant, but if the universe recollapses, that will be equally horrific for its inhabitants. The scene will simply make better headlines as the universe shrinks back into the cosmic maelstrom that was the fireball from which it was born. Dear Merlin,
Enclosed is a tiny calendar as a gift from us. Printed on the upper half is
From the Demings
ALICE & BOB
Y'all come to see us
Just peel off the back and you can stick it on the dashboard of your car.
ALICE AND BOB DEMING
Thank you, Alice and Bob. Your hospitality is befitting of your residence in the state of Texas. Unlike most Texans, however, Merlin does not drive a car. Merlin has other ways of getting around the galaxy, none of which don a dashboard. Dear Merlin,
What is your mission on Earth?
LOS ANGELES, CALIFORNIA
Merlin is just visiting this planet. While here, Merlin intends
1. To be friendly and conversational.
2. To attract cosmic queries from all interested readers.
3. To help enlighten Earth residents about their rich scientific past and present.
4. To introduce readers, on special occasions, to some of Merlin's friends.
5. And to promote truth, justice, and the cosmic way.
Excerpted from Just Visiting This Planet by Neil De Grasse Tyson. Copyright © 1998 by Neil de Grasse Tyson. Excerpted by permission of Main Street Books, a division of Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.