The Times, They Are A-Changin'

This month in particular, you may wonder: what’s with the dates and times listed on the front of the star chart? Why is the chart best at different times on different days? It all has to do with the Earth’s orbit around the Sun.

Of course we’ve all seen how the sky changes overnight as the Earth rotates causing stars to rise and set. What’s less obvious is that from night to night the Earth also moves in its orbit around the Sun - just a little bit.

This is why we see different constellations during different seasons. Right now, it’s spring in the Northern Hemisphere, and it’s easy to find the constellation Leo the Lion in the early evening, high in the southeast. So, Leo is often described as a “springtime” constellation. Compare that to six months later, in the fall, when the Earth is on the opposite side of the Sun from where it is now. Leo will be up during the daytime, and the Sun’s light will block our view.

It’s easy to see differences in the night sky months apart, but the changes are more subtle from day to day. If you watched carefully, you’d find that each day, stars set about 4 minutes earlier than they did the day before. It doesn’t sound like a lot, but it adds up over time. In just 15 days, stars set about an hour earlier. Over the course of a month, that’s two hours difference. That means that the constellations you see at 10:00 PM on the first of this month are the same ones that you see in the same position in the sky at 8:00 PM on the first of the next month.

Add up those minutes over 365¼ days and you get 24 hours - one full rotation of the Earth. The constellations you see tonight are the same ones you’ll see one year from tonight.

Look back at the front of this month’s chart, and you’ll notice something odd, though. According to the chart, this is the sky at 9:00 PM on April first, and 9:00 PM on April 15. What’s going on? Daylight Saving Time, that’s what. Most of the United States “springs forward” at 2:00 am, Sunday, April 2, 2006. So this month’s chart represents the sky at 9:00 PM Standard Time on April 1, and 10:00 PM Daylight Time on April 2.

Now, you might be tempted to say it’s really 9:56 PM on April 2nd, once you take into account the four minutes. True enough, but it’s usually pointless to time things down to the minute. Few of us need that sort of accuracy. The positions of the dots on our star chart certainly aren’t that precise. Besides, exact rise and set times also depend on your exact location on Earth.

If this all sounds really complicated, relax! None of these little details are really important for just going outside and enjoying the night sky. If you’re a few minutes late, don’t worry. The stars will still be there; they’re not moving that fast! Just take your time. The cosmos will wait.

April Planets

Mars continues speeding through the constellations this month, growing fainter all the time. Over the course of the month, it moves from just between the tips of the horns of Taurus the Bull, into the legs of Gemini the Twins.

Meanwhile, bright Saturn hardly moves at all this month, parked next to the Beehive Cluster (M-44) near the center of Cancer the Crab. The Beehive is a great target for binoculars, but to see Saturn’s rings clearly, you’ll need at least a small telescope. If you don’t have a telescope, join us for one of the FREE public star parties listed below.

Jupiter moves through the constellations almost as slowly as Saturn. It rises in the southeast earlier every evening - by about four minutes each night. (Sound familiar?) At the beginning of April, it rises before 10:00 PM Daylight Time. By the end of April, rise time for Jupiter is before 8:00 PM. It lies near the constellation of Libra the Scales, which will be difficult to locate without clear, dark skies far away from light pollution. Fortunately, Jupiter shines brightly enough to make its presence known without help.

Spring Star Parties

FREE public star parties are scheduled throughout the Spring. Members of the Barnard-Seyfert Astronomical Society will provide telescopes and commentary on the Moon, planets, and other objects that might be visible. Mark your calendar, and hopefully, we will have clear skies.

• Saturday, April 1, 2006, 8:00 to 10:00 PM at the Special Events Field at Edwin Warner Park
• Saturday, April 22, 2006, 8:00 to 10:00 PM at the Visitors Center at Longhunter State Park
• Saturday, May 6, 2006, 8:30 to 10:30 PM at the Adventure Science Center
• Saturday, May, 20, 2006, 8:30 to 10:30 PM at the Visitors Center at Longhunter State Park

Hey, Hey, Hey, it's Astronomy Day!

Saturday, May 6, 2006, is Astronomy Day at the Adventure Science Center. Observe the Sun, learn about telescopes, and meet astronomers from MTSU and Austin Peay State University. Be Blown Away by the wild world of weather or investigate Hubble’s Images of the Infinite in the Sudekum Planetarium. Discover our neighbors in space with JPL Solar System Ambassadors, explore the universe, and more.