June 2000 Sky from the Keeble Observatory
June 2000 Sky from the Keeble Observatory
Frequency, a film which I haven’t seen but which has been favorably reviewed in print and broadcast media, poses the interesting question of whether one could communicate with (and actually change) the past. Leaving aside for the moment whether or not the film gives an entertaining answer, let’s look a bit at whether the question even makes sense, and whether or not the answer could be "yes."
In truth, we are all time travelers. However, we seem all to be heading in the same direction, and at about the same speed. Travel at different speeds and directions in time has been a staple of science fiction at least since H.G. Wells’ The Time Machine. In that classic novel, the main character explores the distant future of humankind, returns to his drawing room in the Victorian "present" before vanishing again to rescue his fair maiden in the far future. Star Trek aficionados are familiar with frequent plot lines in which the Enterprise travels into our present. Can any of this happen?
First, changing the rate of advancing time is relatively easy, yet not very interesting. Einstein’s Special Theory of Relativity, confirmed by nearly a century of experimental data, tells us that observers in relative motion experience time at different rates, with the "faster" observer experiencing the "slower" time. So, if you want to age more slowly, take a fast trip to a nearby star and come home. You’ll be younger than your friends left behind. How fast? Ah, there’s the rub. You’d need to travel at a speed at least 10% that of light to get as much as a 5% change (3 minutes per hour). To slow time by half, you’d need to achieve 87% of light speed, and it only gets harder the more you want to slow your clocks!
General Relativity, Einstein’s theoretical structure for gravitation tells us that time passes more slowly deep in a gravitational field. So, you age more slowly in the basement than on the roof. However, not by enough to be noticed. We can measure such differences with extremely precise atomic clocks, but they are minute fractions of a second on Earth. We get a better confirmation of this effect in observing light from white dwarf stars (roughly one solar mass, but about the size of Earth) where the surface gravity is about a million times what we experience. It has even been confirmed in observations of material approaching the event horizon of a black hole!
So, we can change the rate of forward progress in time, albeit with great difficulty. Next question: can we go backwards? We’ll work on that one next month.
Lunar phases for June: All times are EDT. New Moon on the 2nd at 8:14 am; First Quarter on the 8th at 11:29 pm; Full Moon on the 16th at 6:27 pm; Last Quarter on the 24th at 9:00 pm.
This will again not be a great month for observing planets. If you want to see more than one at a time, get up before sunrise! Jupiter and then Saturn will be rising about an hour before the Sun on June 1, about 2 ½ hours before sunrise by month’s end. These planets will remain in the constellation Taurus for the rest of the year. Both are currently on the far side of the Sun from Earth, so it will be six months or so until they are good evening targets. Mercury is barely visible in the early evening. Though it’s about 10 degrees off the horizon, it fades quickly through the first three weeks as it pulls away from us on its faster orbit about the Sun.
An overhead view at about 10:30 at mid-month finds Bootes (the Herdsman) at zenith. The brightest star in this constellation is Arcturus. To the north, the "Big Dipper" in Ursa Major is standing almost on the "bowl" of the dipper. Following the "handle" upwards will lead your eyes to Arcturus. Due west, we find the bright Regulus in Leo (the Lion), while – at about the same elevation off the horizon – Spica in Virgo marks the south-southwest. Antares ("against Mars") is a bit lower in the south-southeast, marking the heart of Scorpio (the Scorpion). Vega, Deneb, and Altair mark a triangle to the east. Deneb is at the head of Cygnus (the Swan). Looking like a cross, tipped on its side, this constellation is in the general direction of the Sun’s motion about the center of our Galaxy. The imaginary line curving from Deneb through Altair and Antares marks out the plane of the Milky Way. Another imaginary line, this one from Antares through Spica and Regulus marks the plane of the ecliptic, the path the Sun, Moon, and planets follow across the sky. Since the Earth is also a planet, this plane is the plane of our own orbit about the Sun.