Radar has been used to observe hundreds of asteroids. It will be the closest an object of this size has gotten to us in 13 years.
Scientists have been waiting for this near-Earth asteroid, known as 2014 JO25, since it first appeared as a fuzzy ball in the Catalina Sky Survey in May 2014.
This asteroid's approach is the closest in at least 400 years - and it's not predicted to come this close again until at least the year 2500.
The asteroid's surface reflects about twice as much light as the moon. The asteroid, known as 2014 JO25, will pass by Earth Wednesday.More news: British lawmakers set to approve PM May's June 8 election plan
The massive space rock will be making its closest pass to Earth in more than four centuries. The last time such a sizable asteroid came this close was in 2004.
Even if you have a decent telescope and know where to look - rolling west across Coma Berenices - mostly cloudy skies will hide its passage in the night sky.
Shantanu Naidu, a NASA scientist who led the Goldstone observations, described the asteroid as, "a contact binary structure", meaning it has two main portions that are connected by a neck-like region. A giant asteroid is hurtling toward Earth, but the folks at NASA say there is no chance it could hit us.
For stargazers, the asteroid will be visible in the night sky after 19 April through small telescopes, before fading away into the cosmic void after a day or two. Although both celestial bodies will not collide with Earth, the asteroid is still frightening especially because of its size.
An asteroid more than a quarter mile wide will pass close to Earth today.