2021: The Giants at Opposition!

(L-to-R) Jupiter, Saturn, Uranus, and Neptune will reach opposition at some point this summer and fall. The planets will be far apart in the sky but are shown together in this composite image scaled to their relative sizes on opposition date. Your actual view in the telescope will differ. Jupiter & Saturn © Chuck Pavlick (Celestron 9¼ Edge HD with 2.5x Powermate and ZWO ASI 224MC camera), and Uranus & Neptune © Dane Hankin (Celestron NexStar 6SE with 2.5x Powermate and ZWO ASI 224MC camera).
Opposition: Earth and outer planet line up on the same side with Sun (bottom of diagram). Conjunction: Earth and outer planet line up on opposite sides of the sun (top of diagram). Courtesy NASA/JPL-Caltech.

An “opposition” happens on the day that Earth and an outer planet line up on the same side of the Sun. For Earth observers, a planet in opposition will rise when the Sun sets and will be in the sky all night. Around the time of opposition, the planet is brightest, practically fully illuminated, and displays the largest angular diameter for the year. Right before, during, and after opposition are prime-time for viewing and imaging a planet!
 
Amateur and large observatory scopes can do best when imaging planets at opposition. It was just announced this summer that amateur astronomer Kai Ly discovered an unknown moon of Jupiter while examining opposition images taken with the 3.6-meter Canada-France-Hawaii Telescope at Mauna Kea Observatory in Hawaii. This news comes just in time to take some confirmation images as Jupiter opposition season is upon us now!
 

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This Week: Neptune Opposition 2018 and Comet 21P!

Neptune image by Voyager 2 probe. NASA/JPL

With the moon a waning crescent, it is a good time to pick out some faint objects in the sky.

On Friday, September 7th, Neptune rises opposite the sun and is closest to earth. Being in the sky all-night, and at it’s brightest, presents a good opportunity to sight this rarely-seen telescopic planet. Unlike the naked eye planets, you’ll have to crank-up the power to make sure you’ve really found it. Even at 100x it just looks like a magnitude 7.8 star. So don’t expect to see a Voyager 2 quality image through your eyepiece.

Click on image to enlarge. Neptune (dots showing position from Sept. 5 to 12) is just south of a line between Phi- and Lambda-Aquarii. In early September it will be moving slowly toward the Lambda star. Using your finder, or a wide-field eyepiece, setup your field on the stars labeled by magnitude inside the 5° circle. Over the course of the week, Neptune will be approaching a line drawn between the mag. 7.5 and 7.4 stars shown. Neptune will be slightly dimmer than both at mag. 7.8.  83-Aquarii it is the brightest of the stars labeled by magnitude — shining at  mag. 5.5 — and will help you orient the chart.

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Neptune Opposition: Sept. 5, 2017

Neptune image by Voyager 2 probe. NASA/JPL

Tonight Neptune rises opposite the sun and is closest to earth. Being in the sky all-night, and at it’s brightest, presents a good opportunity to sight this rarely-seen telescopic planet. Unlike the other planets, you’ll have to crank-up the power to make sure you’ve really found it. Even at 100x it just looks like a magnitude 7.8 star. So don’t expect to see a Voyager 2 quality image through your eyepiece. Continue reading “Neptune Opposition: Sept. 5, 2017”