Category: Astronomy

Exploring the cosmos

Mercury Transit

Both of the planets that orbit closer to the Sun, Mercury and Venus, can be seen to cross the face of the Sun if everything lines up just right. The last transit of Venus was in 2012. It has been much longer since a transit of Mercury, that last occurred in 2006.

Transit of Mercury
The 2006 transit of Mercury, photographed with a 90mm telescope and a Canon 20Da

In comparison the the rare transits of Venus, transits of Mercury are fairly common. There are 13 or 14 transits of Mercury each century, meaning there is a transit on average every seven years. On May 9th this year we have another chance to observe a Mercury Transit.

Photographing the Transit
Photographing the 2006 transit of Mercury from Tucson
Back in 2006 I took the day off work and photographed the transit from my backyard in Tucson. As a transit is a five hour event the effort to observe the entire thing takes a while.

Mercury is quite small with respect to the Sun. During the transit the planet will be a mere 12-13 arcsec across. Considering the Sun is about 1920 arcsec across, the planet will be a fairly small dot on the face of the Sun.

In some respects a transit is the clearest view of Mercury small telescope users are able to view. Normally observed low on the horizon, the innermost planet never gets far from the Sun. During transit a fairly sharp disk can be seen, far better then the mushy view offered near the horizon at sunset and dawn.

First Contact 11:12 UT 1:12 HST
Second Contact 11:15 UT 1:15 HST
Mid-Transit 14:57 UT 4:57 HST
Third Contact 18:39 UT 8:39 HST
Last Contact 18:42 UT 8:42 HST

2016 May 09 Mercury Transit
Unfortunately for observers in the middle of the Pacific the 2016 transit will begin well before dawn. It is only the last hour or so of transit that will be easily visible as the morning Sun rises into the sky. Viewers in eastern North America and Europe will have a better vantage point for this transit.

Please exercise caution when viewing the Sun! Use appropriate eye protection or indirect observing techniques to project an image of the Sun. The link at the start of this paragraph leads to a great discussion on viewing the Sun safely. As always the single best source on the web (or anywhere) for eclipse and transit information is Fred Espenak’s eclipse website at NASA. Stop by whenever you have a question on upcoming events as well as viewing and photography tips.

The next Mercury transit will occur November 11, 2019. This next transit also favors Europe as mid transit occurs at 15:20UT. For the next Venus transit? You are out of luck as it occurs in 2117, over a century away.

New Hypervelocity Binary Star Challenges Dark Matter, Stellar Acceleration Models

W. M. Keck Observatory press release…

A team of astronomers at the Friedrich Alexander University led by Péter Németh has discovered a binary star moving nearly at the escape velocity of our galaxy. There are about two dozen so-called hypervelocity stars known to be escaping the galaxy. While all of them are single stars, PB3877 is the first wide binary star found to travel at such a high speed. Additionally, the results of the new study challenge the commonly accepted scenario that hypervelocity stars are accelerated by the supermassive black hole at the galactic center. The findings are being published in the Astrophysical Journal Letters today.

PB3877 Binary
PB3877 is a hyper-velocity wide binary star zooming through the outskirts of the Milky Way galaxy. This image shows its current location as well as our Sun.
The team, in collaboration with researchers from the California Institute of Technology, showed the binary cannot originate from the Galactic Center, and no other mechanism is known that is able to accelerate a wide binary to such a high velocity without disrupting it. They therefore hypothesized there must be a lot of dark matter to keep the star bound to the Milky Way galaxy; or the binary star, PB3877, could be an intruder that has been born in another galaxy and may or may not leave the Milky Way again.

PB3877 was first reported to be a hyper-velocity, hot compact star, when it was discovered form the Sloan Digital Sky-Survey (SDSS) data in 2011. New spectroscopic observations were done with the 10 meter Keck II telescope at W. M. Keck Observatory on Maunakea, Hawaii and with the 8.2 meter Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile.Caltech astronomers Thomas Kupfer and Felix Fürst observed PB3877 with the ESI Instrument fitted on the Keck II telescope.

“When we looked at the new data, much to our surprise, we found weak absorption lines that could not come from the hot star,” Kupfer said. “The cool companion, just like the hot primary, shows a high radial velocity. Hence, the two stars form a binary system, which is the first hyper-velocity wide binary candidate.”

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