{"id":370,"date":"2011-08-14T00:00:44","date_gmt":"2011-08-14T00:00:44","guid":{"rendered":"http:\/\/www.skycaramba.com\/blog\/?p=370"},"modified":"2011-08-13T22:20:36","modified_gmt":"2011-08-13T22:20:36","slug":"mercury-venus-earth-and-the-sun-line-up","status":"publish","type":"post","link":"https:\/\/www.skycaramba.com\/blog\/2011\/08\/14\/mercury-venus-earth-and-the-sun-line-up\/","title":{"rendered":"Mercury, Venus, Earth, and the sun line up"},"content":{"rendered":"

SkyCaramba weekly astronomy blog for the week ending August 20, 2011<\/em><\/p>\n

\"Mercury<\/a>Mercury and Venus are in conjunction with the sun this week. That means they would all appear to be very close together in the sky if we could see them all. They\u2019re actually far apart. Mercury is between us and the sun. Venus is on the far side of the sun.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Mercury and Venus are the so-called inferior planets. That\u2019s not saying other planets are better. The term simply means they orbit the sun closer than the earth.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The orbits of the inferior planets make their apparent motion in our sky somewhat different than those of the superior planets. That different behavior earned them the inferior<\/em> moniker 2,000 years ago. That was long before sky watchers had a modern astronomical understanding of why their motion is so different.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Because the inferior planets orbit closer to the sun than Earth, they never reach opposition. That\u2019s the point in the sky where a planet is opposite the sun. So you will never hear of Mercury and Venus being up all night.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 However far a planet seems to be from the sun on the dome of the sky, the distance is called its elongation. A planet at opposition is close to 180\u00b0 from the sun. But Mercury and Venus never get anywhere near that mark. Mercury gets as far away as 27\u00b0 and Venus gets to be about 46\u00b0 at the most. Those points are called greatest elongation<\/em>.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Because Mercury\u2019s so close to the sun, its greatest elongations happen six to nine weeks apart. They alternate from morning to evening views and these are the best times to see the planet. Mercury\u2019s next greatest elongation isn\u2019t so great though. It\u2019ll be just 18\u00b0 from the sun in the morning sky on September 3.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Venus takes longer to go around the sun. It can have five months to over a year between greatest elongations. It\u2019ll be highest in the evening sky 46\u00b0 from the sun next March 27.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 All the planets occasionally pass close the sun from our perspective. When the superior planets do it, they\u2019re on the other side of the sun. But the inferior planets could be on the other side of the sun or they could be between the sun and Earth. When they\u2019re on the other side, it\u2019s called superior conjunction<\/em>. When the planet passes between us and the sun it\u2019s at inferior conjunction<\/em>.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 There\u2019s another way the inferior planets are different. Look at them in a telescope and you\u2019ll see them go through phases a lot like the moon does. Like the moon, sometimes the dark sides of Mercury and Venus are pointed toward us.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 In the next few weeks, you may be able to see a white dot following its own path among the stars in the morning sky. Mercury will first move away from the sun, then toward it again. And over the next few months, you\u2019ll see a bright white object emerging into the evening sky as Venus swings into view again.<\/p>\n","protected":false},"excerpt":{"rendered":"

There are two ways Mercury and Venus can be in conjunction with the sun. And they’re demonstrating each this week.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[6,29,88,184,186,4,30,90,166,185,187,17],"_links":{"self":[{"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/posts\/370"}],"collection":[{"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/comments?post=370"}],"version-history":[{"count":2,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/posts\/370\/revisions"}],"predecessor-version":[{"id":373,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/posts\/370\/revisions\/373"}],"wp:attachment":[{"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/media?parent=370"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/categories?post=370"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.skycaramba.com\/blog\/wp-json\/wp\/v2\/tags?post=370"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}