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

Asteroid 5 Astraea at opposition

Dominic Ford, Editor
From the Asteroids feed

Objects: 5 Astraea
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The sky at

Asteroid 5 Astraea will be well placed, lying in the constellation Cancer, well above the horizon for much of the night.

Regardless of your location on the Earth, 5 Astraea will reach its highest point in the sky around midnight local time.

From Ashburn, it will be visible between 19:20 and 05:19. It will become accessible at around 19:20, when it rises to an altitude of 21° above your eastern horizon. It will reach its highest point in the sky at 00:19, 67° above your southern horizon. It will become inaccessible at around 05:19 when it sinks below 21° above your 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 5 Astraea 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 5 Astraea lies opposite to the Sun in the night sky, the solar system is lined up so that 5 Astraea, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 5 Astraea.

On this occasion, 5 Astraea will pass within 1.132 AU of us, reaching a peak brightness of magnitude 9.1. Nonetheless, even at its brightest, 5 Astraea is a faint object beyond the reach of the naked eye; binoculars or a telescope of moderate aperture are needed.

Finding 5 Astraea

The chart below indicates the path of 5 Astraea 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 5 Astraea at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 5 Astraea 08h06m00s 16°33'N Cancer 9.1

The coordinates above are given in J2000.0.

The sky on 20 Jan 2020

The sky on 20 January 2020
Twilight ends
Twilight begins

25-day old moon
Waning Crescent


25 days old

Rise Culm. Set
Mercury 07:56 12:48 17:40
Venus 09:21 14:52 20:23
Moon 03:30 08:39 13:42
Mars 04:05 08:51 13:38
Jupiter 06:16 10:59 15:42
Saturn 07:03 11:52 16:42
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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