When Will The Milky Way Collide With Andromeda?

Read More

How Come I See Fewer Stars Than I Remember As A Child?

I’m past eighty years old. I remember as a child the stars looking like they were almost on top of us, so close and so bright and a billion of them to boot. Now they look so far away and almost faint. No it is not my eyesight. Have the stars moved away from us to that extent in just 80 years and if so how long before they are not seen at all.
The constellation Orion, imaged at left from dark skies, and at right from Orem, UT. Orem, UT is hardly a large city. This is intended to highlight the fact that light pollution is a problem everywhere, not just in cities with tens of millions of inhabitants. Image credit: Flickr user jpstanley, CC BY 2.0.

The constellation Orion, imaged at left from dark skies, and at right from Orem, UT. Orem, UT is hardly a large city. This is intended to highlight the fact that light pollution is a problem everywhere, not just in cities with tens of millions of inhabitants. Image credit: Flickr user jpstanley, CC BY 2.0.

Originally posted at Forbes!

Unfortunately, the stars haven’t moved, and I believe you that it’s not your eyesight either, because there’s another known and astronomically obnoxious thing that’s happened over the past decades. The amount of light pollution in the night skies has increased dramatically in the past few decades, which is largely because there are a lot more lights, illuminating our cities with no particular care for the darkness of the sky.

The increase in lighting is generally a good thing – well lit streets make people feel safer walking at night, for instance. However, the typical streetlight sends a lot of light up into the night sky, and not just down onto the sidewalks and streets. We also do a lot more lighting up of entire buildings now than we used to, several decades ago, and that light reflects off the building into the night sky. With the advent of cheap, bright LEDs, many of these lights are getting even brighter.

Marina Bay Sands, Singapore, at night. Singapore’s light pollution is so severe that the entire population will never use their night vision. Image credit: Leonid iaitskyi, CC A-SA 3.0.

Marina Bay Sands, Singapore, at night. Singapore’s light pollution is so severe that the entire population will never use their night vision. Image credit: Leonid iaitskyi, CC A-SA 3.0.

The combination of all the streetlights, spotlights, and building lights work together to fade our night sky. The more light pollution there is, the less black the night appears – the sky will only darken to a gray – and the more light pollution, the fewer stars are visible.  The faintest stars fade out rapidly, and relatively soon, there are only a few stars which remain.  

If you make it out to a truly dark spot, the stars of your childhood are still there – literal thousands of them, filling the night sky. But many people who live in cities have no way to get out to see the night sky in a remote area, so the dark, glittering sky is either a distant memory or feels like an experience they will never get to grasp.  This isn’t uncommon. It’s now estimated that 30% of the world’s population cannot see the Milky Way from their homes. This goes up to 80% if you live in North America.

We could make some improvements – the loss of the Milky Way doesn’t have to be permanent. We could choose to not illuminate the sky quite so much while we continue to light the streets for safety reasons.  Shielding the light so it can really only shine down would be an easy first step.  Switching off the lights that light up an entire building – even for a few hours in the middle of the night – would help any would-be meteor shower watchers getting up to watch the sky.  Any improvements we can make will bring the night sky back to everyone.  In the mean time, we’ll have to push for more lighting improvements, so that the only dark skies aren’t just in remote wildernesses.  If you’re ever in a dark area, far from a city, remember to look up.

Have your own question? Feel free to ask! Or submit your questions via the sidebar, Facebook, twitter, or Google+.

Sign up for the mailing list for updates & news straight to your inbox!

What is the speed of light equivalent to?



The speed of light in a vacuum is a constant of our universe; no matter where you are or how you’re moving, light will always travel at the same speed.

But what is that speed? It’s 299,792,458 meters per second, or 299,792.458 kilometers per second. Really fast.

Using the speed of light can be quite convenient for astronomical purposes, because we can begin to use it as an extremely long ruler. Since the speed at which light travels is always the same in the vacuum of space, the distance it will cover in a fixed amount of time is also always the same. If you’re driving 60 miles an hour exactly, then it will always take you exactly one hour to travel 60 miles. It’s the same principle with light, except on a much grander scale.

The distance between the Earth and the Sun is about 93 million miles, or 149.6 million kilometers. Light travels about three hundred thousand kilometers a second, but even at that insane speed, the distance between the Earth and the Sun is large enough that there will be lag. A little over 8 minutes of lag, in fact. 8 minutes isn’t very long, but it’s certainly noticeable. To get to Jupiter from the Sun, light takes 43 minutes - to get to Saturn, it’s about 80 minutes - almost an hour and a half. Mars gets light from the sun about 12.5 minutes later, and Neptune, the most distant major planet in our solar system, has to wait about 250 minutes - a little over four hours.

This kind of time delay is something all scientists working with spacecraft orbiting other worlds (or roving on their surfaces) must deal with. The delay will be at minimum 8 minutes less than the numbers above, but depending on where the planets are in their orbits, it can be significantly longer. It’s the root behind the “Seven Minutes of Terror” video NASA released before the Curiosity rover landed; they knew the rover should have landed, unfolded, and radioed home, but they had to wait seven minutes for light to make the trip between Earth and Mars.

Most distances in astronomy are too small to be using light minutes, seconds, or hours. The nearest star to our own is four light years away. From the Sun to the center of our galaxy is about 30,000 light years. Our galaxy is so large that it would take about 100,000 years for light to travel from edge to edge. And the distances between galaxies are even greater.

Have your own question, or find something here unclear? Feel free to ask! Or submit your questions via the sidebar, Facebook, twitter, or Google+.

How much of the universe are we looking at?

Are we scanning the whole universe, or mostly only looking at one place?

At any given moment, it depends on what we’re trying to do! There are a lot of telescopes currently operating, and where we point those telescopes on is entirely dependent on what science the person using the telescope wants to do. So those telescopes wind up looking all over the place, but mostly for short periods of time.

Then there are what’s called “deep fields”, where we point a telescope at one patch of sky for a long time.  This allows us to see very faint objects, and lets us get a lot of detail or capture very distant objects.  The Hubble Deep Field (and Ultra Deep Field) is probably the most famous of these kinds of observations.

But the last kind of observation we can do is an “all sky survey”.This is where we get one telescope to observe every patch of sky available from the location of the telescope. (If the telescope is in space, then that’s ALL the patches of sky - one of many reasons we love space telescopes.)  Depending on the telescope we’re using, we get information about a different type of object, so there have been lots of these surveys to look at different colours of light.  The most recent of these to hit the news was the Planck satellite.  It conducted an all-sky survey to look at the oldest light in the universe, and in the process made a fantastic map of the Milky Way.

In fact, most of those edge-on maps of the Milky Way are made through these all-sky surveys. Some surveys want to avoid the Milky Way, so they skip the region of sky where we know the galaxy is, since getting rid of our galaxy when you’re interested in much more distant objects can be a pain.

Here’s a fun website where you can scroll through a few of the surveys that have looked at our Milky Way in different wavelengths, and see how our view of the Galaxy changes. (It’s zoomable!)

Have your own question? Feel free to ask! Or submit your questions via the sidebarFacebook, or twitter.

Sign up for the mailing list for updates & news straight to your inbox!