Distance and Time and the Speed of Light
Looking up into the night sky, you can’t help but feel completely overwhelmed realizing that you are on a small planet in a such a huge Universe. Light, a strange cosmological constant and the fastest thing in the Universe at 186,000 mi/sec, bows to this enormity. It takes some time to travel those great distances; even billions of years. If the sun were to explode right now, we wouldn’t know it. This is because the light from the explosion must travel so far to get to us. We would have to wait 8.3 minutes before we even knew of the explosion.
If you were 70 million light years away and looked back at Earth with a high - powered telescope, you would see the Earth 70 million years ago. There wouldn’t be any humans. Instead, dinosaurs would be roaming the Earth! This is because the light that left Earth at the time of the dinosaurs, traveling through space like a wave from a stone thrown in a pond, has reached the 70-million-year milestone. If you were there, you would begin to see the Earth evolve from that point in time. The light from 100 million years ago has past your milestone so you would have missed that.
So, we can think of space as something like a time machine. Space is so vast that we can only see the light that left each object out there from a very distant past. In fact, scientists use that fact to explore the structure of the early universe!
When you look at a constellation, like the Big Dipper, the stars look like they are dots on a blackboard but, in fact, they are often millions, even billions of light-years away from each other along your viewing line. If you were just about anywhere except Earth, because of that, the star patterns would be very, very different.
The fact that light, fast as it is, takes time to move even an inch makes you wonder about reality. When you look at someone you are not seeing them now, you are seeing them a little earlier than now.
We are all in a time machine looking back at the past while living NOW.
Heavenly Outlook: The Plane of the Ecliptic, the Zodiac, and the Celestial Equator: Finding your way around the Universe.
The Plane of the Ecliptic is the plane that cuts the Sun’s equator and roughly describes the early disc of matter revolving around the Sun from which most planets were formed (Figure). It also roughly describes the orbital path of the Sun. Planets seem lined up across the sky at some angle to an east-west line (local latitude circle) because the Earth is tilted about 23 degrees off the vertical from its orbital plane. That tilt causes our seasons; when tilted toward the sun we have Summer and when tilted away, Winter.
The Celestial Sphere (Figure) along with accurate time is used to find moving planets and other astronomical objects. Navigators on Earth use latitude and longitude to find a location. Astronomers use that same concept to locate these objects essentially extending that Earth “grid” into the Heavens. They use terms like declination (like latitude) and right ascension (like longitude) to find those heavenly objects. The Celestial Equator is an extension of the Earth’s equator into the Heavens.
Astronomers use the Zodiac to broadly describe the location of Earth on its orbit. As the Earth orbits around the Sun, the tilted Celestial Equator slices through different portions of the sky. That’s why you don’t see Orion in Summer but Scorpio instead. The ancient Zodiac is twelve Constellations that are close to the Plane of the Ecliptic (Figure). To be a little more accurate with timing the orbit modern astronomers have added a thirteenth constellation, The Spear Holder. That month-long period of the ancient Zodiac was roughly when, before sunrise, the constellation would rise and set ensuring that the constellation was “in the House of the Sun” even though they could not see it. Those dates are roughly 6 months from when we see them at night. Beware, the astrological Zodiac periods are not current but were determined thousands of years ago when the Earth’s orientation with respect to the Plane was much different.
Can we spot the Plane of the Ecliptic this month? Yes! Saturn, Jupiter, and Venus are among the brightest objects in the June sky and visible right after dusk. If you draw a line through them, you will see the tilted Plane of the Ecliptic. So, find a few bright Planets and draw a line through them, not from Planet to Planet, and you will see the broad outline of the disk of “rubble” from which our Solar System and you were formed.
Thanks to Deborah Byrd at Earth and Sky for bringing this idea to my attention. Nice website!