Staying in the sky

Let’s try something a little different this month. We will talk about artificial satellites – and why they “stay” up there. Go outside – maybe in the summer when it’s warmer – and throw a rock up in the air – but not straight up – lest it come back down and hit you on the head. It will rise, travel a distance away from you, and inevitably fall back down. Makes sense. Gravity does that.

Now, as long as it’s safe, let’s throw the rock higher and harder. Of course, it will go further from you before it comes back down. But it will come down. Gravity does that. Next, if we take a handgun or rifle – again in a very safe place, and fire it up and away from you, the bullet will travel up and away from you – very swiftly! – but it will come down. Gravity does that.

Even big guns in the military, which can fire a projectile many miles away, will still have that projectile come down – and unfortunately cause great damage where it lands. Again gravity pulls it back to Earth.

In the early days of rockets – the 1940s and 1950s, they fired higher powered rockets up in to the atmosphere, further and further, but the story did not change.

Gravity did that. But they went much further before they fell back, perhaps over a continent, or an ocean. But, as we said gravity is always there.

Now, let’s try to stretch the imagination. We add a little more power to our rocket. Again, after the rocket engine quit, the rocket will start to fall back. Gravity does that.

But this time, it has gone so far before it falls back, that instead of just crossing an ocean, or even half the earth, it actually misses the earth!

But it is still falling back – as it falls, it just keeps missing the earth, and in doing so keeps falling around the earth and bingo, we have a satellite.

So, actually, gravity, by always pulling “things” back down, makes it possible to have satellites.

To complete this idea – or fact – if we fire our satellite higher and higher, it will take longer and longer to fall back – as it always does, until it takes long enough to fall back, that it is falling at the same speed that the earth turns, and it will stay stationary in our sky – over the same place – or as we call it, a geostationary satellite.

Finally, if we fire our rocket still harder, it will still fall, but in falling, it will fall away from the earth or carry on out into space. Gravity always makes things fall down. So Isaac Newton told us.

Now back to earth. What is in the sky this month.

As always, let’s look at the planets first and we will begin with the night sky.

It’s a lonely night sky this month. Only Mars is there in the night for us. It is slowly getting smaller, dimmer, and a little lower in the sky each month, but not by much. To see it, look in the Southwest a few hours after sunset. It sets a little after 11 p.m. at the first of the month, and before 11 p.m. by month’s end.

In the a.m., during the course of the month, we can see Venus, Jupiter, Saturn and Mercury. Let’s start with Venus. As the month begins, Venus rises some 3 ½ hours before sunrise in the South Southeast. As the month progresses, it dims a little and ends the month slightly less high in the sky.

Jupiter rises about 1 ½ hours after Venus, in the southeast. It rises slightly higher and brightens a little during the month. And this month, while Jupiter is rising, Venus is dropping in the sky and on Jan. 22 they are as close together as they will get.

Saturn will only become visible in the third week of the month, low in the east-southeast. While we began by also saying Mercury was visible in January in the dawn, but it really cannot be seen after the fourth of the month.

But, what is exceptional this month? On the night of Jan. 20 – 21, we will experience a total Lunar Eclipse. The moon will be very high in the sky for this eclipse. The totality will begin at 12:41 a.m., after midnight, but of course there is much to see before that, with the lightest shadow – the Penumbra – beginning at just after 11 p.m. and partial dark eclipse at 11:34. It will all be over by 3:15 a.m. DON’T MISS IT. It will be great. Let’s hope for no clouds. New Moon – Jan. 6.

Full Moon – Jan. 21 and of course that is the lunar eclipse. We’ll, see you next month.