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Want to see Uranus? July 4 could be your best chance in decades
The Red Planet and Uranus will appear close together before dawn on Independence Day morning.
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Want to see Uranus for yourself? Independence Day morning offers one of the best opportunities in decades, as the distant ice giant passes extraordinarily close to Mars in the predawn sky.
Although we often hear that only five planets are visible to the unaided eye, Uranus can also be seen from Earth under the right conditions. As the seventh planet from the sun, it is very faint — near the threshold of naked-eye visibility at roughly sixth magnitude — so viewing it requires a very dark sky with little to no significant light pollution.
The second challenge is knowing exactly where to look. Uranus is faint enough to blend into a background of similarly dim stars, but early on Saturday, July 4, at around 4 a.m. local daylight time, Mars provides a useful guide. On that Independence Day morning, Mars and Uranus will appear unusually close together in the sky.
Mars currently rises about half an hour before the first light of dawn. It is still relatively faint at about magnitude +1.3, and through a telescope it appears tiny, measuring less than 4.5 arc seconds across. Look for it low in the east-northeast, about 5.5 degrees directly below the Pleiades star cluster.
Uranus should resemble a tiny greenish star and will appear only about 1/63 as bright as Mars. Although Uranus is nearly 7.5 times larger than Mars, it is more than 9.5 times farther away as seen from Earth. At about 1.88 billion miles (3.02 billion km), it appears only slightly smaller than Mars in apparent size, measuring about 3.5 arc seconds across.
According to Belgian celestial calculator Jean Meeus, Mars and Uranus will be closest at 5 a.m. Universal Time (UTC) on July 4, when only 6 arc minutes will separate them. For comparison, Mizar — the middle star in the Big Dipper's handle — and its fainter companion Alcor are separated by about 12 arc minutes. In other words, Mars and Uranus will appear only half as far apart as Mizar and Alcor.
Observers with exceptionally sharp vision and very dark skies may want to try spotting Uranus near Mars without optical aid, though binoculars or a small telescope will make the view much easier.
Mars and Uranus are in conjunction on average once every 2.38 years. But meetings as close as this one are quite rare, occurring on average once about every 40 years. The next similarly close approach between these two worlds that is readily visible in a dark sky is not due until Dec. 8, 2147!