Crescent Moon meets Mars
Crescent Moon meets Mars (Chris Vaughan, Starry Night Education)
This Week’s Sky: May 11 to 17

Get out your cameras — this is a beautiful time for planets.

This sure looks like the week of the planets. Neptune, Mars, Saturn and Jupiter dance through the pre-dawn sky together, joined by the waning Moon that dwindles to a crescent by Saturday.

Monday, May 11 pre-dawn – Bright Moon and planets

Bright Moon and planets (Chris Vaughan, Starry Night Education)

In the southeastern sky during the hours before sunrise on six consecutive mornings this week, the bright, waning Moon’s orbital motion from west to east (or right to left as viewed from the Northern Hemisphere) will carry it closely past three bright planets — Jupiter, Saturn and Mars.

Although not visible with unaided eyes, it will pass Neptune, too. On Monday morning, May 11 look for the Moon positioned 1.4 outstretched fist diameters to the right (or 14 degrees to the celestial west) of bright, white Jupiter. Yellowish Saturn and reddish Mars will be arrayed to the left of Jupiter. The scene will make a fine wide-field photograph when composed with some interesting landscape scenery.

Monday, May 11 pre-dawn – Saturn stands still

Saturn stands still (Chris Vaughan, Starry Night Education)

On Monday, May 11, Saturn will temporarily cease its regular eastward motion in front of the distant stars of Capricornus and begin a retrograde loop (red curve with dates/times) that will last until the end of September.

The apparent reversal in Saturn’s motion is an effect of parallax produced when Earth, on a faster orbit, passes the Ringed Planet on the “inside track.” The pause in Saturn’s eastward apparent motion will allow Jupiter to approach to within 4.75 degrees of Saturn, well within the field of view of binoculars (red circle). The two gas giants will slowly separate after this week.

Monday, May 11 overnight – Asteroid Pallas pauses

Asteroid Pallas pauses (Chris Vaughan, Starry Night Education)

On Monday, May 11, the main belt asteroid designated 2 Pallas will pause in its regular eastward motion in front of the distant stars, and begin a retrograde loop (red curve with dates) that will last until early September. The asteroid has that “2” in front of its name because it’s the is the second asteroid to have been discovered (after 1 Ceres). It’s also the third largest in the asteroid belt.

Pallas’ visual magnitude of 10.1 will allow it to be seen in amateur telescopes during the hours after midnight. On May 11, Pallas will be positioned only half a degree above the medium-bright star Sham, the higher of two stars that form of Sagitta, the Arrow’s feathers. The asteroid and those stars will appear together in the eyepiece of your telescope (red circle).

Tuesday, May 12 pre-dawn – The Moon near Jupiter and Saturn

The Moon near Jupiter and Saturn (Chris Vaughan, Starry Night Education)

The Moon’s trip past the morning planets will continue on Tuesday, May 12 in the southeastern sky during the hours before sunrise. After 24 hours of travel eastward, the Moon will now sit several finger widths below (or three degrees to the celestial south of) bright Jupiter. Somewhat dimmer and yellowish Saturn will be positioned less than five degrees to their left (east) — and reddish Mars can be spotted well off to the left (east) of the trio. The arrangement will offer another lovely photo opportunity. On the following two mornings, the waning Moon will travel the gap between Saturn and Mars.

Thursday, May 14 pre-dawn – Jupiter goes retrograde

Jupiter goes retrograde (Chris Vaughan, Starry Night Education)

On Thursday, May 14, Jupiter will cease its regular eastward motion in front of the distant stars of eastern Sagittarius and begin a retrograde loop (red curve with dates) that will last until mid-September. The apparent reversal in Jupiter’s motion is an effect of parallax produced when Earth, on a faster orbit, passes Jupiter on the “inside track”. After this week Jupiter’s 4.75 degree angular separation from Saturn, well within the field of view of binoculars (red circle), will slowly increase.

Thursday, May 14 at 14:03 GMT – Last Quarter Moon

Last Quarter Moon (Chris Vaughan, Starry Night Education)

The Moon will reach its last quarter phase at 14:03 GMT on Thursday, May 14. At last quarter, the Moon rises around midnight and remains visible in the southern sky during morning daylight. Because they form a 90-degree angle with the Sun and Earth, last quarter moons are illuminated on the eastern side, towards the pre-dawn sun. At that time of its orbit, the moon is also positioned ahead of the Earth in our trip around the sun. About 3.5 hours later, Earth will occupy that same location in space. After this phase, the waning Moon will traverse the final quarter of its orbit around the Earth, on the way to New Moon.

Friday, May 15 pre-dawn – Crescent Moon meets Mars

Crescent Moon meets Mars (Chris Vaughan, Starry Night Education)

In the southeastern sky on Friday morning, May 15 between about 4 a.m. local time and sunrise, the Crescent Moon will appear three finger widths to the lower left (or 3.25 degrees to the celestial southeast) of reddish Mars. Saturn, Jupiter and Neptune will share the sky with Mars and the Moon, but dim and distant Neptune will not be visible without a telescope. The morning meet-up will offer another fine photo opportunity featuring the moon and bright planets.

Saturday, May 16 pre-dawn – Moon and planets trace out the Ecliptic

Moon and planets trace out the Ecliptic (Chris Vaughan, Starry Night Education)

This month’s visit of the bright planets by the Moon concludes on Saturday, May 16 with the Crescent Moon positioned 1.3 fist diameters to the lower left (or 13 degrees to the celestial east) of Mars in the southeastern sky before sunrise. Jupiter and Saturn will be paired up further to the west. Dim, distant and blue Neptune will be located a palm’s width to the upper left of the Moon.  The three bright planets, plus the yet-to-rise Sun, will nicely define the plane of our Solar System across the sky (green line). The Moon’s five-degree orbital inclination allows it to stray by up to that distance from the Solar System’s plane — at this time, below it. The Moon will still be close enough to the planets to warrant yet another wide-field photograph. Try to capture the Moon’s trip on all six consecutive mornings. You can also send your best photos to SkyNews’ Photo of the Week contest.

Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.

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