Look toward the southeast on Thursday night (May 3) about an hour after sunset, and you will behold a rare and beautiful sight, a triple conjunction of the moon, the planet Saturn, and the bright star Spica.
A conjunction occurs when two or more astronomical objects are close together in the sky. In reality they are far apart in space; their closeness is just an effect of perspective. In astrology such close encounters are supposed to cause serious effects, but astronomers know that conjunctions are nothing more than a beautiful sight and a photo opportunity.
Because Saturn is the farthest planet from the sun visible to the naked eye, its movements in our sky are very slow. It has been in the constellation Virgo, close to Spica, for a couple of years now. The moon, on the other hand, is very close to Earth, so appears to move relatively quickly across the sky.
Conjunctions like this one provide an excellent opportunity to see how rapidly the moon moves from night to night. On Thursday night, the moon will be well to the right of Saturn and Spica. Twenty-four hours later, on Friday night, it will be well to the left of Saturn and Spica.
Skywatchers take note: The biggest full moon of the year is due to arrive this weekend.
The moon will officially become full Saturday (May 5) at 11:35 p.m. EDT. And because this month's full moon coincides with the moon's perigee — its closest approach to Earth — it will also be the year's biggest.
The moon will swing in 221,802 miles (356,955 kilometers) from our planet, offering skywatchers a spectacular view of an extra-big, extra-bright moon, nicknamed a supermoon.
And not only does the moon's perigee coincide with full moon this month, but this perigee will be the nearest to Earth of any this year, as the distance of the moon's close approach varies by about 3 percent, according to meteorologist Joe Rao, SPACE.com's sky watching columnist. This happens because the moon's orbit is not perfectly circular.
This month's full moon is due to be about 16 percent brighter than average. In contrast, later this year on Nov. 28, the full moon will coincide with apogee, the moon's farthest approach, offering a particularly small and dim full moon.
Though the unusual appearance of this month's full moon may be surprising to some, there's no reason for alarm, scientists warn. The slight distance difference isn't enough to cause any earthquakes or extreme tidal effects, experts say.
However, the normal tides around the world will be particularly high and low. At perigee, the moon will exert about 42 percent more tidal force than it will during its next apogee two weeks later, Rao said.
The last supermoon occurred in March 2011.
To view this weekend's supermoon to best effect, look for it just after it rises or before it sets, when it is close to the horizon. There, you can catch a view of the moon behind buildings or trees, an effect which produces an optical illusion, making the moon seem even larger than it really is.
From SpaceWeather:What a weekend to be a sky watcher!
Earth is entering a stream of debris from Halley's Comet, source of the annual eta Aquarid meteor shower. The shower peaks this weekend on May 5th and 6th. Glare from a perigee full Moon--a "Super Moon"--will interfere with the display. Nevertheless, observers especially in the southern hemisphere could still see dozens of meteors during the hours before local sunrise on May 6th.