As you gaze upon a starlit sky it is easy to forget that it is actually a dynamic changing celestial sphere.
To the casual observer, the stars they see tonight were the same as the ones they saw last night and will be approximately the same they will see in ten years time, but look closely and you will see evidence that the Universe is changing and evolving right before your eyes.
A great example is visible to observers in north-eastern United States in the early hours of Thursday morning (20th March) at around 2:06 a.m. ET, when asteroid 163 Erigone will pass directly in front of Regulus, the brightest star in the constellation Leo.
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Events like these, which are known as occultations, are not terribly rare, but the brightest ones that can be seen with the naked eye are far less common. Regulus, which is the brightest star near the ecliptic, has been occulted by solar system bodies before. Venus occulted the star in 1959, but it will not be until 2044 when the planet occults it again. On Thursday, asteroid 163 Erigone, which is about 72 kilometers (45 miles) wide will pass directly between Earth and Regulus blocking it from our view.
The asteroid, which will be over 177 million kilometers (110 million miles) from Earth at the time of the occultation, is not visible to the naked eye. Instead, it will require a telescope at least 15 centimeters (5.9 inches) in diameter to pick out the elusive visitor. However, as Regulus is a bright star, its absence means the event requires no astronomical equipment to enjoy.
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For telescope owners, however, you can make scientifically valuable observations by accurately measuring the time when the star disappears and then reappears. From knowing observers' locations, these timings can help to build up a more accurate profile of not only the asteroids orbit but also that of its shape and size.
One of the great things about this occultation is that it is going to be visible from a highly populated part of the world so that potentially millions of people can witness it.
The occultation is first visible from a point in the mid-Atlantic at 01:53 a.m. ET before being visible on land for the first time at Long Island, New York and New Jersey around 02:06 EDT. The shadow cast by Erigone will cover a 120 kilometer (75 mile) wide band across Earth as it races northward heading over Lake Ontario and Canada before passing almost directly between the cities of Toronto and Ottawa and on to Hudson Bay.
Finally at about 02:22 EDT the shadow will leave the Earth having (hopefully) inspired millions of sky watchers, helping us realize that our Cosmos is far from being a static place.