My Dark Sky

Now is a good time to observe planets. All the planets are visible either after dusk or before dawn, except for Mercury, which is too near the Sun to observe this April.

Just after dark, Mars and Saturn are high up in the sky in Gemini and Leo respectively. Mars, although is bright, shining at magnitude 1, is not at all impressive through telescope. Its angular size has shrink since its opposition last Christmas, from 16 arc-second to a mere 6 arc-second now. Currently, Mars is best appreciated just with the naked eye, as a bright red beacon in the sky.

The next planet is more interesting. Saturn, shining brightly at magnitude 0.4, is 2.5 times brighter than Regulus, the brightest star in Leo, which is slightly to the west. Even through a small telescope, Saturn’s rings are easily visible. However, its appearance will change significantly in a couple of years. Saturn rings are “closing” now. We are approaching the “ring plane crossing” period, when the planet’s ring system will tilts edge-on to Earth. Since the rings are so thin, when they are edge-on to us, it seems that the rings have disappeared when view through small telescopes.

Saturn’s gorgeous rings span 44″ in diameter. Look for the dark Cassini Division that divides the A ring and B ring. Saturn’s disk itself is about 19″. Larger telescope and steady seeing will reveal subtle atmospheric features on Saturn. Also look for the planet’s shadow as it falls on the rings’ far side.

Another easy target when observing Saturn through any telescope is Titan, Saturn’s largest moon. 8th-magnitude Titan will appear as a point of light somewhere near Saturn. Other moons that are also visible are Rhea, Tethys, Dione, Iapetus and Enceladus. Click here to find the location of the moons.

Bonus: Not far to the southeast from Saturn, we have a gibbous Moon. Although the Moon will not disturb our observation of Saturn, the bright glow from our Moon may drown the light from Saturn’s moons. So this may not be a good time to see Saturn’s moons.

Finish? Then go to sleep now. You have to wake up early tomorrow morning to continue the marathon. Set your alarm clock to 6 am.

Let’s continue…

By 6:30 am Jupiter, Neptune and Uranus are up in the sky, whereas Venus is just rising from the east. If you can’t wait until 6 am to see Jupiter, you can actually start observing Jupiter when it rises to reasonable height about 3 am.

Although Jupiter rises at about 1:30 am, it is too near the horizon for detail observation. Usually the best view of a planet is when it is high up in the sky, clear from the horizon. When a planet is low near the horizon, it has to go through more atmosphere and hence more turbulent which tends to blur out details. Light pollution and obstructions such as buildings, trees and mountains near the horizon also hinder observations.

Jupiter now lies in eastern Sagittarius, shining at magnitude -2.2. Jupiter’s disk is about 39″, slightly smaller than Saturn’s rings. It is now big enough to show lots of details in small telescope. Especially prominent is Jupiter’s dynamic atmosphere, featuring parallel bands to the equator across its disk.

Any telescope will show the four biggest moons of Jupiter: Io, Europa, Ganymede and Callisto. They are known as the Galilean moons, because they are first discovered and observed by Galileo. As the moons orbit around Jupiter, there will be times when they pass in front of Jupiter – this is known as transit – and times when they pass behind – occult by Jupiter.

The positions of the moons change every night. It is actually fun to watch them dance around the giant planet: sometimes three moons on one side and one on the other side, sometimes two on each side, sometimes only three moons are visible while another one is “hiding” behind Jupiter.

The next planet is Neptune, which lies in Capricornus, one constellation east of Sagittarius. Neptune shines at magnitude 7.9, so it is not visible to the naked eye. A binoculars or telescope is needed to spot it. It’s not easy, because Neptune appears star-like in binocular; it looks the same as the background stars. However, due to its nearer distance to us, it can actually give itself away by moving against the background stars. So observe the same area for few nights up to a week or two while plotting down accurately the stars in the field of view. Compare those plots and find the “star” that moved. The “star” that moved is Neptune.

Another constellation east in Aquarius is Uranus. Shinning at magnitude 5.9, Uranus is barely visible to the naked eye. Uranus, same as Neptune, appears star-like in binocular.  However, since Uranus is bigger than Neptune and also nearer, a medium-sized telescope under reasonably steady skies will show its small greenish-blue disk, revealing it as a planet and not a star.

And lastly, the brightest of all planets, is the morning “star” – Venus, shining at magnitude -3.8. If the eastern horizon is clear, Venus is too bright to be missed. Even as the sky brightens, Venus still be able to pierce through, usually mistaken by many people as a man-made satellite.

Oh oh, one more… as the Sun rises, look down at your feet, and you will see the most familiar planet of all – mother Earth.

Click on photo to enlarge

This picture is taken last October during a trip to Jelawang Waterfall and Gunung Stong in Kelantan, Malaysia. This is a view on top of the Jelawang Waterfall where the campsite is located. The very bright point of light near the top of the picture is Venus, and to the left, barely visible, is Saturn.  Credit: thChieh (APGM).

~ by thChieh on April 17, 2008.

Posted in Observations & Tips