© NASA/Galileo 1993. Pictured asteroid is 243 Ida.

Asteroid 115 Thyra at opposition

Dominic Ford, Editor
From the Asteroids feed

Objects: 115 Thyra
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The sky at

Asteroid 115 Thyra will be well placed, lying in the constellation Perseus, well above the horizon for much of the night.

Regardless of your location on the Earth, 115 Thyra will reach its highest point in the sky around midnight local time.

From Fairfield, it will be visible in the evening sky, becoming accessible around 17:40 (EST), 30° above your north-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 23:07, 89° above your southern horizon. It will continue to be observable until around 05:30, when it sinks below 21° above your north-western horizon.

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The geometry of the alignment

This optimal positioning occurs when it makes its closest approach to the point in the sky directly opposite to the Sun – an event termed opposition. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time.

At around the same time that 115 Thyra passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest in the night sky. This happens because when 115 Thyra lies opposite to the Sun in the night sky, the solar system is lined up so that 115 Thyra, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 115 Thyra.

On this occasion, 115 Thyra will pass within 0.977 AU of us, reaching a peak brightness of magnitude 9.7. Nonetheless, even at its brightest, 115 Thyra is a faint object beyond the reach of the naked eye; binoculars or a telescope of moderate aperture are needed.

Finding 115 Thyra

The chart below indicates the path of 115 Thyra across the sky around the time of opposition.

It was produced using StarCharter and is available for download, either on dark background, in PNG, PDF or SVG formats, or on a light background, in PNG, PDF or SVG formats.

The position of 115 Thyra at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 115 Thyra 03h14m40s 40°54'N Perseus 9.7

The coordinates above are given in J2000.0.

The sky on 27 November 2021
Twilight ends
Twilight begins

23-day old moon
Waning Crescent


23 days old

Rise Culm. Set
Mercury 06:55 11:37 16:20
Venus 10:21 14:46 19:12
Moon 22:50 06:01 13:03
Mars 05:32 10:33 15:33
Jupiter 12:04 17:16 22:28
Saturn 11:17 16:10 21:04
All times shown in EST.


The circumstances of this event were computed from orbital elements made available by Ted Bowell of the Lowell Observatory. The conversion to geocentric coordinates was performed using the position of the Earth recorded in the DE430 ephemeris published by the Jet Propulsion Laboratory (JPL).

The star chart above shows the positions and magnitudes of stars as they appear in the Tycho catalogue. The data was reduced by the author and plotted using PyXPlot. A gnomonic projection of the sky has been used; celestial coordinates are indicated in the J2000.0 coordinate system.

Image credit

© NASA/Galileo 1993. Pictured asteroid is 243 Ida.






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