Published: 2013-08-23 17:02:00
Updated: 2013-08-23 18:34:50
Posted August 23, 2013
By Tony Rice
You may have received email or seen posts on Facebook or other social media sites telling of a rare opportunity to observe Mars next week. They claim that Mars will appear so large that it might be mistaken for a second moon, 2287. This sounds like an amazing opportunity but, unfortunately, none of it is true.
Don't wake the kids that night. None of what is described will happen this year, nor will it happen in 2287 or any other year. Mars is about twice as large as the moon, but it is also over 900 times further away. The orbits of Earth and Mars never bring the planets close enough to create conditions described in the email. Mars doesn't even rise for more than 3 hours after the moon.
Astronomers measure the apparent size of celestial objects using degrees (90 degrees from the horizon to directly overhead), arc-minutes (60 arc-minutes in a degree) and arc-seconds(60 arc-seconds in an arc-minute). The apparent diameter of the moon is currently 30 arc-minutes or about half the width of your pinky with your arm fully extended. The apparent diameter of Mars is about 4 arc-seconds or about 450 times smaller than the moon appears.
These claims resurface about this time each year. They originated with exaggerations about what a remarkably close pass of Mars and Earth on Aug. 27, 2003, would look like. In reality, Mars was a beautiful sight that night with surface features visible even to small telescopes. However, claims that Mars and the moon would appear similar in size were off by a factor of about 74.
With fewer evening clouds over the coming week, it is still a good time to get out and enjoy the night sky though. During the coming week, the International Space Station (ISS) will pass over the area. It will rise from the north west before disappearing from view in the Earth's shadow minutes after it rises.
For the latest on visibility of the ISS from the area, follow @ISSpassRaleigh on Twitter.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.