Tag: ephemeris

Preparing for Comet C/2012 S1 ISON

Astronomers, professional and amateur alike, are getting ready for comet C/2012 S1 ISON, possibly the highlight of a year that has already seen several good comets.

Discovered in September 2012 by Vitali Nevski and Artyom Novichonok, of the ISON project, a group of telescopes dedicated to discovering and tracking solar system objects. The comet was then an 18th magnitude object in the outer solar system, an impressive find for a small telescope.

Comet C/2012 S1 ISON
An image of comet C/2012 S1 ISON acquired by the Hubble Space Telescope on October 9th, 2013, credit: NASA, ESA, and the Hubble Heritage Team
When astronomers first calculated the comet’s orbit they found a surprise. The comet will pass close to the Sun. Not just close, but extremely close! On November 28th the comet will pass perihelion, its closest approach to the Sun. At a mere 1,860,000km (1,150,000miles) this will be a close pass indeed. As perihelion is measured from center to center, the distance is even closer if you consider the 695,500km (432,200mile) radius of the Sun. Subtracting the solar radius you realize the comet will pass a mere 1,165,000km (724,000miles) above the surface of the Sun. At this distance the intensity of the solar radiation will be nineteen thousand times more intense than a sunny day on Earth.

The next surprise was hinted at by the orbital calculations. The orbital solution indicated a nearly hyperbolic path, suggesting that this was a new comet, one that had not visited the inner solar system before. This possibility was strengthened by later observations of the comet.

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Asteroid 2008 QE2 Ephemeris

Planning to make a go at photographing asteroid 2008 QE2 as it passes the Earth. Before I can do that a little planning is in order. Minor questions… Is it above the horizon near close approach, in my nighttime sky? It turns out this object will be available for observation.

The table below is a precision ephemeris generated by the NASA HORIZONS web interface for Mauna Kea on the island of Hawai’i. Listed are celestial coordinates, time, local elevation and azimuth, magnitude and distance. The marks after the time column indicate daylight (*), twilight (A) and moonlight (M).

From the data it is clear that the evening of May 30th (May 31st UT) allows observation from Hawai’i, at an elevation of ~46° a few hours after dark. Nicely placed and nicely timed for observation. Close approach is actually the next day, but the difference is minor. The next evening allows a second chance at the observation while the asteroid is still close.

Comet iPhone App

One drawback to the many iPhone astronomy apps is the lack of large databases. To an advanced amateur such as myself, the lack of detailed databases is a distinct negative in these programs. I venture way beyond the Messier catalog, or even the NGC on a regular basis. I understand the price to be paid in speed and memory required to support larger databases, but I would like to have the option.

C/2007 N3 Lulin
Comet C/2007 N3 Lulin on the evening of 26 Feb 2009, a stack of 10 x 4 min exposures, Canon 20Da and TeleVue 76mm APO
The programs I have seen also lack the ability to display comets or asteroids. This last issue has become a problem lately, as we have several nice comets available in the sky for observing. A quick way to look up the current position for the object is essential for comets and asteroids if you wish to observe them. Last night’s coordinates will have you looking at an empty starfield tonight.

There is one decent answer for comets… I found a very nice app for comet ephemerides published by Keith Yohn. Called simply Comet, this free program downloads the latest ephemeris data from the Minor Planet Center and displays the current and future coordinates for each comet. Just what I needed!

There are no charts, the data is simply displayed in table form. Every observable comet is displayed and can be search for using a simple set of filters.

When attempting to observe comet C/2009 P1 Gerradd a few times recently. I have found the coordinates to be quite accurate. The comet was in the sky, right where the app showed it would be. Nothing like a real world test.