During June, observers can enjoy a striking natural display with the naked eye: a planetary alignment that allows most of the planets to be visible together. This unusual event can be watched from across Spain for several days and into early July. The key to catching it is waking up early, because the phenomenon appears just before sunrise.
Five planets come into view this week in a clear sequence from the horizon upward: Mercury, Venus, Mars, Jupiter, and Saturn. This observation comes from the Royal Observatory of Madrid. In this celestial line-up only Uranus and Neptune remain out of sight, far beyond what the unaided eye can detect.
Though two or three planets sometimes overlap in the sky, it is rare to see five aligned and visible at once. In fact, this alignment has not been seen since 2004 and is not expected again until 2040. NASA notes that a five-planet alignment occurs on average once every 57 years.
At the end of June, the Moon will join the lineup, making the early wake-up even more worthwhile for sky watchers.
The hardest planet to notice is Mercury. Its small size, great distance, and especially its close proximity to the Sun create a strong glare that makes Mercury disappear as soon as the Sun climbs above the horizon.
A planetary alignment happens when several planets appear to lie on a common plane in a straight or nearly straight line as viewed from Earth. This is a two dimensional projection, and the planets would not appear in a line if observed from space.
When to observe the alignment?
The current days work well, but the optimum window is the last ten days of June and the first days of July. Because sunlight washes out the faint planets, observers should start watching about an hour before sunrise.
Where to watch?
Mercury and Venus sit very low on the eastern horizon since they orbit closest to the Sun. A clear coastal view with the sea to the east or a high, unobstructed vantage point without nearby hills is ideal. Look toward the east and southeast for best results.
What should you wear to observe this?
All five visible planets can be seen with the naked eye, so no binoculars or telescope are necessary for the main alignment. With a medium sized telescope (about 200 mm), Uranus and Neptune become visible too, though they are far away and faint.
Is there an app or website to simulate the view?
The Stellarium program offers a free, realistic simulation of the night sky for any date and location. It can be downloaded to a PC or mobile device. After installation, users select their location so the program accurately represents the sky from that spot.
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