How fast

In response to a very good question ™ posed by one of my students, a response. First, the question:

Question

How fast do spaceships or probes or satellites go? How long would it take for them to reach the closest star? The center of the galaxy?

Answer

The Voyager space probes, launched in the late 1970s, went to visit Jupiter and would eventually travel outside of our solar system. It’s actually approaching the Oort Cloud, and the true boundary of the system, called the Heliopause.

Voyager is travelling at about 56 000 km/h [1]. A different source cites a maximum velocity of 62 856 km/h [2]. It’s hard, sometimes, to decipher all of the conflicting information. At any rate, it will reach Proxima Centauri in about 19 000 years. Yawn.

More recently, the New Horizons space probe left Earth at a speed of 58 016 km/h, which is also quite impressive. [3] After passing close by Jupiter, and using something called gravity assist, it was accelerated to a speed of 83,700 km/h. [4] Even more impressive.

However, that’s not the whole story. (Neither is this example, as you will soon see.) The Pioneer 10 probe, sent out in 1972, was also accelerated by Jupiter. It reached a speed of 173 000 km/h. Faster yet.[5]

But there is… another. Launched in the mid 1970s by Germany (and the US), Helios was sent to orbit the Sun. Being accelerated by a mass that’s ten times that of Jupiter means a bit of a boost. Up to 240 000 km/h [6] (wikipedia says 252,792 km/h, but with no sources).

That seems to be the record. And it would take about 4 500 years for it to reach Proxima Centauri. If it were pointed towards there, that is.

Wiki wiki

My wife and I vacationed in Hawaii two Christmases ago. At the Honolulu airport, we were greeted with shuttle buses that brought us to the downtown. They were called “wiki-wikis”.

True story.

Many of you are, of course, familiar with Wikipedia, the online encyclopedia that anyone can edit. If not, then you should go and spend some time on that last link, and get yourself a bit schooled.

What you need to know right now is that I have created a DT Astronomy wiki, which you can find over here. Or here:

The David Thompson Astronomy Wiki

Go explore. (More when there’s more.)

Astronomy Photo of the Day

This site is an addition to my blogroll. It is a site that you should visit on a regular basis. It is, in fact, my starting page ( you know, when FireFox loads).

Astronomy Picture of the Day

Call it APOD. It’s run jointly by NASA and Michigan Technological University.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

This site is changed every day, and every day it’s a new view of heavens – usually with some connection to current events. Today was the Cat’s Eye Nebula

An interesting feature of this site (and one that has won it Internet awards) is the use of hyperlinks. By clicking on the right thing, you can find out more about NGC 6543, the Hubble Space Telescope photos, or planetary nebulae.

And all this besides the fact that the photography is amazing.

Equal Night

Last night, at precisely 11:48 am, a very special thing happened: the Sun crossed Earth’s equator. This is what it looks like, courtesy of Astronomy Picture of the Day:

Now that explanation might not make a whole lot of sense. To understand it, you need to know a few things. Or be reminded of them.

First of all, recall that Earth spins. It spins about an imaginary pole (well, two of them if you include the north and south poles), the official term for which is axis. When that axis is directly up an down (vertical) with respect to our orbit around the Sun, the the Sun shines down directly on the equator.

(Here’s an animation that illustrates what we’re talking about here.)

And that’s what happened last night. The vernal equinox. Equal nights.

The upshot of all this is that spring has sprung. From here on in, the days become longer and the nights shorter. In 91 days we’ll have the longest day (and shortest night) and the days will begin to get shorter again.

Happy spring!

Additional Resources

An explanation of Earth’s Rotation (Wikipedia).
Motion of the Earth (from the Office of Naval Research).