Saturn Occultation

Click on graphic to see it full size.

Click on graphic to see it full size.

   During the course of the day on Tuesday 10 June the waxing gibbous Moon, as it moves eastward along its orbital path, will pass by the planet Saturn. The two will be their closest at 19 UT (2 pm CDT), which for my time zone and latitude is during the daylight hours as well as before the Moon rises. However as the two rise the Moon will be within a few degrees to the east from the planet Saturn making for a striking pair as this graphic is showing.

   saturn-occultationViewing this lunar-planet conjunction from other latitude locations will show the gap between the two to range from as it does from my latitude to no gap at all. The latter would be at latitudes where the viewing angle is such that the Moon occults, or passes in front of Saturn, which relative to the Moon is in the background. From the latitude of Queenstown South Africa (31o 54′ S : 26o 53′ E) observers will be able to see the Moon occult Saturn as this animated graphic is showing.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Smooth With No Bumps

globe3   Yesterday I had the pleasure of spending nearly an hour with a 2nd grade class at one of our local elementary schools talking with them about the night sky, how to use a ‘Big Dipper’ star clock, and other topics that only a 2nd grader could come up with. Prior to my visit they had read the story ‘Follow the Drinking Gourd’ so that was the introduction into apparent sky motions and using the Big Dipper clock. I used the Starry Night program to show how the sky appears to move when facing north and for comparison east, south, and west. They already knew that it was the Earth rotating and not the sky so this led to me telling them that where we live (our latitude) we are moving at nearly 800 mph. I then asked how is it that we don’t feel that speed. After a few responses I had them think about their bus ride to school.
   How did they know the bus was moving? Answers included things moving past the window, bumpy road, and engine noise. I then asked them to imagine a bus ride where there were no windows to look out, a quiet engine, and a smooth ride. How would they know the bus was moving? I asked what they felt when the bus started moving or when it slowed down (changing its speed) and was told that your body moves in the opposite direction when the bus speeds up or slows down. My follow-up was to then ask how is that we do not feel the Earth rotating at nearly 800 mph expecting to hear that the speed of the Earth does not change and instead was told that “there are no bumps as the Earth rotates”. We all agreed that that was an ok answer and then finished by having them reason that there was no change in speed.
   So then we proceeded to use the Law of Cosines to determine the rotational speed of the Earth at different latitudes! Well, not really but just in case any one is interested in how to determine rotational speed at different latitudes here is a basic explanation.
calculator   A good starting point is to determine the rotational speed at the equator, 0 degrees latitude. Using rounded up values the Earth has a circumference of 24,902 miles. It rotates in 24 hours so the circumference divided by the time comes out to 1,038 mph at the Earth’s equator. You then multiply the cosine of your latitude times 1,038 mph.
   How to get the cosine of your latitude? If you do not have access to a calculator or a calculator app but are online you can use Google Search, for example by typing “cosine of 40 degrees”, or whatever latitude you want, and pressing Enter. You will get an answer in a calculator display as this graphic shows.
   So hang on! Oh wait, never mind – “no bumps”.
   
   
Click here to go to the Qué tal in the Current Skies web site for more observing information.

On Top of the World

No, It's Not upside Down!

No, It’s Not upside Down!

   For the past week we have not seen the Sun much – even nights have been cloudy, and the temperature has been below freezing for more than a week. So combining those conditions with thoughts of warmer climes, and recent correspondence (aka e-mail) with a long-time friend living in New Zealand brought back memories of a trip I took with my wife, Sue, to New Zealand to attend an Astronomical Conference in New Zealand.
   Remember the 80’s song by Men at Work that asked the musical question “Do you come from a land down under?” That lyric gained new meaning for me while at that conference. I was politely corrected when I said that I came down to New Zealand. “No, no,” my hosts said, “You came up to New Zealand.”
   Have you ever wondered why we refer to folks from Australia and New Zealand as being from down under? How did their neck of the woods become down under and ours, conversely, up top? How is it that north is assumed to be at the top of the Earth and south at the bottom of the Earth? For that matter, is there really a top or bottom to the Earth?
   Try this: Hold a ball in one hand. Touch the top of the ball with your other hand. Directly opposite this point is the bottom of the ball. Turn the ball around in random directions a few times and again touch the top of the ball. Turn the ball around in random directions a second time and again touch the top of it. Did you touch the same spot on the ball each time? Was the bottom the same each time? So where would the top or the bottom of the ball be? Think of the ball as the Earth and each of the spots that were the ‘tops’ as different places on the surface of the Earth.
Nosotros casa es su casa

Nosotros casa es su casa

   Now try this: Take either a reticulated Earth globe or a globe that can be taken off of its mounting and set it in a large cup or bowl that will serve as the base. Adjust the globe so that your location on Earth is at the top. Mark this location on the globe with a straight pin or matchstick held with putty. Next, rotate the base so that globe’s north pole is aligned with true north and it’s south pole with true south. The Earth globe is now positioned with respect to the Sun exactly as the Earth is positioned in space with respect to the Sun. (Note that the shadow of your marker will mirror the shadows of all other objects cast on Earth with regards to compass direction.) From this ‘space’ perspective, you are clearly at the top of the Earth. Notice what point on the surface of the Earth is directly opposite your location, or at the bottom of the globe.
   If there is land at that location, imagine your counterpart doing this same activity. Who do you think your counterpart would consider to be at the bottom?    Imagine doing this for other locations around the Earth. What does this tell you about where the top and bottom of the Earth is?
   Your answer would have to be based on your frame of reference (you are on top wherever you are). This, unfortunately, is not the traditional way of looking at things around the globe.
"Be Careful Opening the Overhead Bins"

“Be Careful Opening the Overhead Bins”

   It has been a common and accepted convention to think of north as being at the top and south at the bottom. This thinking has established our perceived understanding of our place on the Earth and the vocabulary associated with this line of thinking.
This Northern Hemisphere–bias has even influenced how many astronomy books depict the Moon and constellation patterns. To someone from south of the equator, constellations and Moon phases are upside down according to the Northern Hemisphere–based star maps.
   So, is there actually a top or a bottom to the Earth? It’s up (or down) for you to decide.

   Thanks to Eric Jackson for planting these ideas in my head!
   
   
   
Click here to go to the Qué tal in the Current Skies web site for more observing information.