Earth & Sky

Moon, Saturn, Regulus together on March 18

Saturn, as seen by the Cassini spacecraft.

Tuesday, March 18, 2008

At dusk tonight, the moon hangs over your eastern horizon. It might look full to you, but the full moon this month will come on March 21.

The March 18 moon is what astronomers call a waxing gibbous moon. “Waxing” means the lighted portion visible from Earth is increasing in size. “Gibbous” means that the moon’s disk is more than half-lighted yet less than full as seen from our vantage point in space.

At nightfall, as you gaze toward tonight’s nearly full moon, look for two points of light below the moon. The higher and fainter light is a silvery-blue star, Regulus in the constellation Leo the Lion. The brighter object below Regulus is Saturn, 6th planet outward from the sun in our solar system.

Tonight, Saturn is more than 8 times farther away from Earth than Earth is from the sun. It’s over a billion kilometers – about 750 million miles – away. Despite this distance, even a small telescope enables you to glimpse the glorious rings that make Saturn so fascinating to view. A small telescope also shows Titan, Saturn’s largest moon, as a pinprick of light.

So gaze eastward at nightfall on March 18. Look for the moon, with the star Regulus below it, and Saturn below Regulus. All three bodies swing highest in the sky around mid to late evening, then set in the west in the wee hours Wednesday morning.

By the way, Saturn’s moon Titan is actually larger than the planet Mercury. It’s the only known moon to have a dense, planet-like atmosphere. Scientists think the nitrogen and hydrocarbons in Titan’s atmosphere resemble the makeup of Earth’s primitive atmosphere a few billion years ago. Saturn is the most distant world in our sun’s family that you can see with the eye alone. It shines with a steady, golden light.

Written by Bruce McClure

6 Comments for Moon, Saturn, Regulus together on March 18

1. 1

   Mar 6, 05:39 PM #

   Smartyhead says:

   Ha i am doing my report on saturn just kidding

2. 2

   Mar 9, 02:53 PM #

   joseph molinaro says:

   hi..what is the biggest star in our solar system..on ask .com one said the pistol star where is the pistol star and the other said the star alnath in auriga..also what is the smallest star in our solar system.
   joe

3. 3

   Mar 9, 06:45 PM #

   Bruce McClure says:

   Joe,

   Are you asking about the largest and smallest stars in the galaxy? I’ve read that the Pistol Star is possibly the brightest & most massive star known (that doesn’t necessarily mean largest star, however). Here’s another biggest star article and a radio program about a smallest star candidate.

   Bruce

4. 4

   Mar 18, 02:32 PM #

   Floss says:

   Just to make clear for you the difference between our Solar System and Our Galaxy. In our Solar System the only star is our Sun, hence the name “Solar” system. Our Galaxy, however, is much larger. It is called the “Milky Way” and contains myriads of stars, planets, comets, etc. In fact, everything we see as we look to the heavens belongs to our Galaxy. How many more Galaxys are there in the Universe…does anyone know?

5. 5

   Mar 18, 05:18 PM #

   Bruce McClure says:

   Floss,

   Thanks for clarifying the difference between solar system and galaxy. As to the number of galaxies in the universe, nobody really knows. Estimates place the number in the hundreds of billions.

   Bruce

6. 6

   Mar 19, 03:44 PM #

   Abby says:

   I was watching the moon last night and saw the action but didn’t know what was going on with it. Looking here and getting a better explanation of what went on last night was very interesting and helpful. Thank you