Will Moon and Mars appear the same size this August?

On August 27, 2013, the moon and Mars are expected to appear the same size to the naked eye. That's how the story goes.In the astronomical world, this is called the 'Mars Hoax.'

It all started in 2003, writes Jeff Brush on SouthburyPatch.And here is the full story behind this.The distance between Earth and Mars varies dramatically over time. The maximum distance (when Earth and Mars are on opposite sides of the Sun) is about 250 million miles, and the minimum distance (Earth and Mars on the same side of the Sun, with Earth at its farthest distance from the Sun and Mars at its closest distance, is 33 million miles.

As a result, the apparent size of Mars does vary quite a bit, from a mere speck when seen through a typical telescope, to a small disk. When Mars is at its closest approach, the disk shows some level of detail of the surface of the planet, including large canyons and mountain ranges, though typically still quite blurry when viewed by eye through an amateur's telescope.

Mars comes within [approximately] 50 million miles of Earth once every 18 months or so. Because the orbit of Mars is more elliptical than Earth's orbit, it does occasionally get within 35 million miles, and the time between such closer approaches is measured in thousands of years.

The last closest approach occured on August 27, 2003 at 12:30 a.m. A couple months before that closest approach, a PowerPoint presentation posted on the Internet discussed the event. It is  mentioned therein that the next time Mars will be this close to Earth is in the year 2287, and, in big bold letters, "NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN".

As a result, every July and August since 2003, we see a recurrence of these emails or other Internet message types, carrying the same message. Will anyone live up to see this once-in-a-lifetime event? Mars isn't even visible in our nighttime sky this year (or in most of the years since 2003), concludes Brush.

To read more about this hoax, click here.

Comet ISON may pay a visit to the Red Planet

Around the world, astronomers are anticipating the approach of Comet ISON.A new ScienceCast video anticipates its close flyby of Mars on Oct. 1, 2013. On Thanksgiving Day 2013, the icy visitor from the outer solar system will skim the sun's outer atmosphere and, if it survives, could emerge as one of the brightest comets in years. First, though, it has to fly by Mars.

Astronomer Carey Lisse of the Johns Hopkins University Applied Physics Lab said,"Comet ISON is paying a visit to the Red Planet. On Oct 1st, the comet will pass within 0.07 AU from Mars, about six times closer than it will ever come to Earth."

Mars rovers and satellites will get a close-up view. It's too early to say whether Curiosity will be able to see the comet from the surface of Mars - that depends on how much ISON brightens between now and then. Lisse says the best bet is NASA's Mars Reconnaissance Orbiter. The MRO satellite is equipped with a powerful half-meter telescope named HiRISE that is more than capable of detecting the comet's atmosphere and tail. Observations are planned on four dates: August 20th, Sept 29th, and Oct 1st and 2nd.

The Mars flyby comes at a key time in Comet ISON's journey. It will have just crossed the "frost line," a place just outside the orbit of Mars where solar heating is enough to start vaporizing frozen water. But when ISON crosses the frost line, "the whole comet could erupt in geysers of gas," says Lisse. "Mars orbiters will have a ringside seat."

The amount of outgassing at Mars will give researchers clues to the size of ISON's nucleus, which is hidden from view deep within the comet's dusty atmosphere. McEwen sees this as a tune-up for another comet encounter next year. "The science value of observing Comet ISON is hard to predict. We've never tried such a thing before. However, this is good practice for Comet Siding Spring, which will pass much closer to Mars in 2014."

For now all eyes are on Comet ISON. An unprecedented number of NASA spacecraft - 16 - will be observing the comet. Astronauts on board the International Space Station will be watching, too.

To read more about the comet, click here.