Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into three sections; what you can see with the naked eye, with binoculars, and with a small telescope. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on April 29th. For April, your best viewing nights will be from April 1st to the 4th, and the 19th to the 30th. The Star chart below is set for Florence, SC on April 15th at 9 pm.
There is a total lunar eclipse this month, but note that my heading says eclipses. For the United States there will be four total lunar eclipses in the next 17 months. Dates: April 15, 2014, October 8, 2014, April 4, 2015 and September 28, 2015. For South Carolina, only the April 4, 2015 will not be visible. I will discuss these later eclipses in my columns as they occur. At any given location on Earth, a solar eclipse is rare, but a lunar eclipse can occur at any given location every 2 to 4 years, and partial lunar eclipses are even more common. The possibility that there will be a total solar eclipse at any given location such as Charleston SC is more like once every 100 to 200 years! Note: There is a total solar eclipse over Columbia and Charleston on August 21, 2017; please mark your calendars.
The lunar eclipse this month will occur early in the morning of April 15th. Lunar eclipses are not at all as exciting as a solar eclipse, so most people will step outside to view a lunar eclipse if it occurs conveniently between sunset and about 11 pm. Therefore one may not feel driven to get up between 3 and 4 am to see this eclipse. Later in my discussion I will give you a reason to check out this eclipse.
A lunar eclipse occurs when the shadow of the Earth covers the surface of the Moon. Another definition is when the Earth is lined up exactly between the Sun and the Moon; see image below.
Of course this can only occur during a full Moon. From this description, one might conclude that we should have a lunar eclipse once each month during the full moon and a solar eclipse once each month during a new Moon. The reason this does not occur is that the orbit of the moon is slightly tilted in relation to the plane of the Earth and Sun. So each month, the full Moon usually passes above or below the shadow of the Earth; see diagram below.
You will also note that there are two shadow regions; the penumbra is an area where a portion of the Sun’s light is blocked. The umbra is the area where all of the sunlight is blocked. This description would suggest that when the Moon is fully inside the umbra (total eclipse) the Moon would be dark and not visible. However, during a total lunar eclipse the Moon is darkened, but still visible, usually with a reddish brown color. The reason the Moon is not black/invisible is because the Earth has a significant atmosphere. Our atmosphere has the ability to bend (refract) the sunlight slightly around the Earth. Only light near the red end of the spectrum can make this bend. Another good reason to observe lunar eclipses is that many factors can effect this refraction such as time of night when totality occurs and the amount of dust in the atmosphere. Therefore every lunar eclipse may have a different shade of red and a different brightness.
Now I would like to mention a seldom discussed unique effect that can occur during a lunar eclipse, especially if the eclipse occurs when the Moon is somewhat high above the horizon as it is this April. To understand this effect, we begin with a question. If the Moon is a sphere, why don’t we see it as a three dimensional ball in the sky, instead of a flat disk? The Moon landing cleared up this question, when the astronauts noted that the Moon’s surface is covered with a fine powder. This fine dust tends to diffuse/scatter the bright Sun’s reflected light, which prevents us from seeing the Moon as a ball. Now, during a total lunar eclipse, the Moon is only dimly lit by a small amount of reddish sunlight refracting/bending around the Earth’s atmosphere. Under this low light, the dimensionality of the Moon can sometimes become apparent. Check it out this month, and see if the Moon looks like a ball during this total eclipse. This effect alone makes it worthwhile to set your alarm clocks for 3 am April 15th.
On March 29th we had our second NASA Saturday public viewing at ScienceSouth. Again we were bothered by scattered cloud covering, but the sky was much more favorable than last month. We had good clear views of the planet Jupiter and its colorful cloud bands, and its moons. In addition, we viewed the Orion Nebula and the four young stars in its center (the Trapezium), along with the Pleiades Cluster and the Beehive Cluster. Keep watching the ScienceSouth website for news of future public viewings.
Naked Eye Sights: Check out the total lunar eclipse between 3 am and 4 am on the morning of April 15th.
Binocular Sights (7 to 10 power): Still another great month to view Orion nebula and the Pleiades. Add to your list the Beehive Cluster (M44) in front of the constellation Leo.
Telescope Sights (60-100mm): Try again to see Jupiter’s atmospheric bands and check out the positions of the four Galilean moons. Mars is clearly visible in the east throughout the month. You will need a higher end amateur telescope to enjoy the surface features of this planet.
See you next month!