Notes on the Planets in May 2009

MERCURY will be a difficult object during May. It starts the month in the evening sky, but sets only 40 minutes after the Sun on May 1 making observation virtually impossible. The planet reaches its first stationary point on May 8, after which it will be moving in a westerly sense through the stars, in the opposite direction to the Sun, so rapidly closes in on it.

Inferior conjunction, with Mercury between the Earth and Sun, is on May 19, after which Mercury rapidly moves up into the morning sky. It is stationary for a second time on the morning of May 31 when it will start moving to the east again. By then Mercury will rise a good hour and a half before the Sun, reaching an altitude of 7°, 50 minutes before sunrise. At magnitude 2.3 it is likely to be a difficult object in the brightening sky, although readily visible in binoculars, nearly 30° round to the north from due east. Mercury will also be nearly 30° to the lower right of Venus.

VENUS will be high, bright and obvious in the morning sky before sunrise during May. In the north of New Zealand it rises a little before 4am throughout the month. It will rise about half an hour later in the south. On May 1 Venus will be some 7.5° below Uranus (magnitude 5.9) but it will pull away from the latter planet during the rest of the month. Venus is also within a few degrees of Mars throughout May.

On the morning of May 21 the Moon, a 17% lit crescent will be 7.5° to the left of Venus.

MARS is in the morning sky a few degrees to the lower right of Venus throughout May, so the latter will act as a guide to finding the red planet in the dawn sky. At magnitude 1.2 Mars will have about 1% of the brightness of Venus, so will become a difficult object for the unaided eye within about 40 minutes of sunrise. It will, of course, be observable in binoculars for about another 20 minutes or so.

On the morning of May 22 the Moon, now only 10% lit, will 7° to the lower left of Mars.

JUPITER, will rise before 1am (NZST) on May 1 advancing to about 11pm by the end of the month. By then the planet will be well up and easily visible before the dawn sky brightens too much.

Jupiter will remain in Capricornus throughout May. Its easterly movement will take it towards Neptune which is also in the constellation. They are closest on the morning of May 28 when Jupiter will be less than half a degree above Neptune (magnitude 7.9). The fainter planet should be quite easily visible in binoculars up to an hour before sunrise. A 5th magnitude star, μCap will be slightly further away, to the left of Jupiter. Neptune will scarcely move for a few nights either side of its conjunction with Jupiter, being stationary on May 29. But Jupiter will move noticeably each night compared to Neptune.

In May the Moon joins Jupiter and Neptune when at last quarter on the 17th. By the time the three rise it will be into the early hours of May 18. By then the Moon will be a little less than 50% lit. At 1.30am it will be 5° below Neptune and nearly 6° below Jupiter, with μCap between them, just below Jupiter. By 6.30am the Moon will have moved nearly 2° further away and the sky will have rotated so Jupiter is now to the upper left of the Moon.

SATURN will be well placed for evening viewing during May. At the end of the month it will set a short time after midnight. Transit times, when it is highest in the sky and due north, are about 9pm on May 1 and 7pm on May 31. Being stationary in mid May, Saturn will show little change in position during the month. It will be in Leo about 15° from Regulus, magnitude 1.4. The two will be nearly level mid evening, with the brighter Saturn to the right of the star.

The 76% lit waxing Moon will be a little less than 5° from Saturn on the night of May 4. They are closest early evening, with the Moon moving a little further away from Saturn during the evening. The Moon joins Saturn again on the last day of the month, this time it will be 53% lit with the two being closest about midnight close to the time they set in New Zealand. They are about 5.5° apart at 10 pm.

Saturn's brightest satellite Titan will be eclipsed by the planet twice during May. On the night of May 7 Titan will move into Saturn's shadow about 7:22pm (NZST) and emerge again at about 12:41am NZST. On May 23 the disappearance into eclipse will be about an hour earlier at 6:29pm with the reappearance at 12:07am. This eclipse, which occurs during the RASNZ conference, will be one of the most favourable in terms of the distance Titan is from Saturn when the eclipses occurs. It is also the last at which the disappearance into eclipse occurs during the hours of darkness in New Zealand. More details on observing these events and a table of the times of all the eclipses can be found on the page of eclipses of Titan and Rhea. This page also has details of two shadow transits of Titan across Saturn which take place on May 15 and May 31. Both are partly observable from New Zealand, the start of the transit occur before sunset.